Experimental organic chemistry a miniscale and microscale approach

Contents in Brief 1 Introduction, Record Keeping, and Laboratory Safety 1 2 Techniques and Apparatus 27 3 Solids: Recrystallization and Melting Points 93 4 Liquids: Distillation and Boil

Conical vial Claisen adapter Air condenser Reflux condenser Hickman stillhead

Rubber septum Round-bottom

f lask

with ground-glass joints

Separatory funnel with ground-glass joints

Hirsch funnel

Büchnerfunnel Filter flask

Equipment Commonly Used in the Organic Chemistry Laboratory

First Aid in Case of an Accident

The occurrence of an accident of any kind in the laboratory should be reportedpromptly to your instructor, even if it seems relatively minor

zle toward the base of the flames Burning oil may be put out with an extinguisher

classified for use on “ABC” type fires

If your clothing is on fire, DO NOT RUN; rapid movement will only fan theflames Roll on the floor to smother the fire and to help keep the flames away fromyour head Your neighbors can help to extinguish the flames by using fire blankets,laboratory coats, or other items that are immediately available Do not hestitate to aidyour neighbor if he or she is involved in such an emergency; a few seconds delay may

result in serious injury A laboratory shower, if close by, can be used to extinguish

burn-ing clothburn-ing, as can a carbon dioxide extburn-inguisher, which must be used with care until

the flames are extinguished and only if the flames are not near the head.

If burns are minor, apply a burn ointment In the case of serious burns, do notapply any ointment; seek professional medical treatment at once

C H E M I C A L B U R N S

Areas of the skin with which corrosive chemicals have come in contact should beimmediately and thoroughly washed with soap and warm water If the burns areminor, apply burn ointment; for treatment of more serious burns, see a physician.Bromine burns can be particularly serious These burns should first be washed

with soap and warm water and then thoroughly soaked with 0.6 M sodium thiosulfate

solution for three hours Apply cod liver oil ointment and a dressing; see a physician

If chemicals, in particular corrosive or hot reagents, come in contact with the

eyes, immediately flood the eyes with water from the nearest outlet A specially designed eyewash fountain is useful if available in the laboratory Do not touch the eye The eyelid as well as the eyeball should be washed with water for several

minutes In all instances where sensitive eye tissue is involved in such an dent, consult an ophthalmologist as soon as possible

acci-C U T S

Minor cuts may be treated by ordinary first-aid procedures; seek professional ical attention for serious cuts If severe bleeding indicates that an artery has beensevered, attempt to stop the bleeding with compresses and pressure; a tourniquetshould be applied only by those who have received first-aid training Arrange foremergency room treatment at once

med-A person who is injured severely enough to require a physician’s treatment

should be accompanied to the doctor’s office, or infirmary, even if he or she claims to

be all right Persons in shock, particularly after suffering burns, are often more ously injured than they appear to be

seri-Discovery Experiments

Chapter 3 NEW Formation of Polymorphs, p 109

Melting-Point Depression, p 119

Chapter 4 Comparative Fractional Distillations, p 142

Fractionation of Alternative Binary Mixtures, p 142

NEW Fractional Distillation of Unknowns, p 142 Chapter 5 Separation of Unknown Mixture by Extraction, p 167

Isolation of Ibuprofen, p 167

Chapter 6 Effect of Solvent Polarity on Efficiency of Separation, p 186

Analysis of Plant Pigments from Various Sources, p 186Analysis of Analgesics by TLC, p 187

Column Chromatographic Separation of Benzyl Alcohol and Methyl Benzoate, p 194Analysis of Factors Affecting Retention Times, p 207

Effect of Stationary Phase on Separation of a Mixture, p 207Molar Response Factors of Isomers, p 208

Molar Response Factors of Non-Isomeric Compounds, p 208

Chapter 7 NEW Solvent Effects on Rf-Values, p 218

NEW Iodine as a Catalyst for Isomerization, p 222

Assessing Purities of Dimethyl Maleate and Fumarate, p 222

Chapter 9 Chlorination of Heptane, p 319

NEW Chlorination of 2,3-Dimethylbutane, p 320 Chapter 10 Elimination of Alternate Non-Terminal Alkyl Halides, p 343

Elimination of Stereoisomeric Alcohols, p 355

NEW Analysis of Bromohexanes, p 370 NEW Bromination of (Z )-Stilbene, p 380 NEW Solvent Effects on the Stereochemistry of Bromination, p 380 NEW Substituent Effects on the Stereochemistry of Bromination, p 380, NEW Regiochemistry of Hydroboration/Oxidation of an Acyclic Alkene, p 394

Regio- and Stereochemistry of Hydroboration/Oxidation of a Cyclopentene, p 394

Chapter 11 Preparation of 3-Methyl-3-hydroxy-2-butanone, p 412

Chapter 12 Hydrolysis of Anhydrides, p 432

Chapter 13 NEW Effect of pH on Kinetic vs Thermodynamic Control, p 453

Chapter 14 Analysis of SNReactions as a Function of Substrate, p 469

Effect of Temperature on Rates of Solvolysis, p 487Effect of Leaving Group on Rates of Solvolysis, p 487

Chapter 17 Hydrogenation of 4-Cyclohexene-cis-1,2-dicarboxylic Acid, p 567

Formation and Reduction of N-Cinnamylidene-m -nitroaniline, p 573Reduction of 4-tert-Butylcyclohexanone, p 583

Reduction of Benzoin, p 584

Chapter 18 Preparation of (Z )- and (E )-Stilbenes by a Wittig Reaction, p 606

Wittig Reaction of 9-Anthraldehyde, p 609Preparation of a Stilbene by the Horner-Wadsworth-Emmons Reaction, p 620Preparation of trans, trans-Dibenzylideneacetone, p 621

Chapter 19 NEW Exploring the Influence of Mode of Addition, p 656

NEW Preparation and Characterization of a 3° Alcohol, p 659 Chapter 22 Preparation of Polystyrene, p 770

Stability of Polystyrene toward Organic Solvents, p 772Polymers and Water, p 772

Cross-Linking of Polymers, p 773

4

1 n I

8

1 n S

4

2 l

7

2 b

111

(272.15)RgRoentgenium

2

1

) 7

2 (

2 (

2 (

117

(?)UusUnunseptium

Approximate 1 H and 13 C NMR Shifts

* C H 3 groups typically resonate 0.3–0.4 ppm upfield of the corresponding

C H 2 groups; C H groups are typically 0.3–0.4 ppm further downfield of the

C H 2 group.

*

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Experimental Organic Chemistry,

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1 2 3 4 5 6 7 13 12 11 10 09

Contents in Brief

1 Introduction, Record Keeping, and Laboratory Safety 1

2 Techniques and Apparatus 27

3 Solids: Recrystallization and Melting Points 93

4 Liquids: Distillation and Boiling Points 127

12 Dienes: The Diels-Alder Reaction 421

13 Kinetic and Thermodynamic Control of a Reaction 445

14 Nucleophilic Aliphatic Substitution: Preparation of

Alkyl Halides 461

15 Electrophilic Aromatic Substitution 491

16 Oxidation of Alcohols and Carbonyl Compounds 537

17 Reduction Reactions of Double Bonds: Alkenes, Carbonyl

Compounds, and lmines 563

18 Reactions of Carbonyl Compounds 601

19 Organometallic Chemistry 639

20 Carboxylic Acids and Their Derivatives 669

21 Multistep Organic Synthesis 703

22 Polymers 765

23 Carbohydrates 787

24 ␣ -Amino Acids and Peptides 803

25 Identifying Organic Compounds 833

26 The Literature of Organic Chemistry 905

Table of Contents

Chapter 1 Introduction, Record Keeping, and Laboratory Safety 1

Historical Highlight: The Importance of Record Keeping 24

Chapter 2 Techniques and Apparatus 27

2.22 Heating Under Reflux 81

Melting Points 117

A Calibration of Thermometer 117

B Determining Capillary-Tube Melting Points 118Melting-Point Depression 119

Historical Highlight: Polymorphism 122

Chapter 4 Liquids: Distillation and Boiling Points 127

Boiling Points of Pure Liquids 129

Miniscale Procedure 129Microscale Procedure 130

Simple Distillation 133

Miniscale Procedure 133Optional Procedure 134Microscale Procedure 134

Fractional Distillation of a Binary Mixture 141

Miniscale Procedure 141Comparative Fractional Distillations 142Fractionation of Alternative Binary Mixtures 142Fractional Distillation of Unknowns 142

Chapter 5 Extraction 153

Base and Acid Extractions 161

Miniscale Procedure 161Microscale Procedure 164Separation of Unknown Mixture by Extraction 167Isolation of Ibuprofen 167

Isolation of Trimyristin from Nutmeg 172

Miniscale Procedure 172Microscale Procedure 173Historical Highlight: Natural Products 175

Chapter 6 Chromatography 179

Separation of Spinach Pigments by TLC 184

Effect of Solvent Polarity on Efficiency of Separation 186Analysis of Plant Pigments from Various Sources 186

Separation of Syn- and Anti-Azobenzenes by TLC 186

Chapter 7 Stereoisomers 213

Separation of Diastereomeric 1,2-Cyclohexanediols 217

Solvent Effects on Rf-Values 218

Isomerization of Dimethyl Maleate to Dimethyl Fumarate 220

Miniscale Procedure 221Microscale Procedure 221

Iodine as a Catalyst for Isomerization 222Assessing Purities of Dimethyl Maleate and Fumarate 222

Properties of the Enantiomeric Carvones 225

Resolution of Racemic 1-Phenylethanamine 230

Miniscale Procedure 231Historical Highlight: Discovery of Stereoisomers 234

Chapter 8 Spectral Methods 237

Free-Radical Chain Chlorination of l-Chlorobutane 317

Miniscale Procedure 317Microscale Procedure 318Chlorination of Heptane 319Chlorination of 2,3-Dimethylbutane 320

Relative Rates of Free-Radical Chain Bromination 326

Historical Highlight: Keeping It Cool 333

Chapter 10 Alkenes 337

Base-Promoted Elimination of an Alkyl Halide 340

A Elimination with Alcoholic Potassium Hydroxide 341Miniscale Procedure 341

Microscale Procedure 341

B Elimination with Potassium tert-Butoxide 343

Miniscale Procedure 343Elimination of Alternate Non-Terminal Alkyl Halides 343

Dehydration of Alcohols 352

A Dehydration of 4-Methyl-2-Pentanol 352Miniscale Procedure 352

B Dehydration of Cyclohexanol 353Miniscale Procedure 353

Microscale Procedure 354Elimination of Stereoisomeric Alcohols 355

Addition of Hydrogen Bromide to 1-Hexene 368

Miniscale Procedure 369Microscale Procedure 370Analysis of Bromohexanes 371

Bromination of (E)-Stilbene 377

Miniscale Procedure 377Microscale Procedure 378

Bromination of (E)-Stilbene: The Green Approach 378

Miniscale Procedure 379Microscale Procedure 379

Oxidation of a Cyclopentene 394Microscale Procedure 394

Regiochemistry of Hydroboration/Oxidation of an Acyclic Alkene 395Regio- and Stereochemistry of Hydroboration/

Oxidation of a Cyclopentene 396Historical Highlight: Additions Across Carbon-Carbon␲-Bonds 399

Preparation of 3-Hydroxy-3-methyl-2-Butanone 412

Miniscale Procedure 412

Formation of a Silver Acetylide and Its Decomposition 417

Historical Highlight: Acetylene: A Valuable Small Molecule 418

Table of Contents ix

Chapter 12 Dienes: The Diels-Alder Reaction 421

Diels-Alder Reaction 426

A Reaction of 1,3-Butadiene and Maleic Anhydride 426Miniscale Procedure 426

Microscale Procedure 427Miniscale Procedure for Microwave Option 427

B Reaction of 1,3-Cyclopentadiene and Maleic Anhydride 428Miniscale Procedure 428

Microscale Procedure 429

C Hydrolysis of Anhydrides 430

1 4-Cyclohexene-cis-1,2-dicarboxylic Acid 430

Miniscale Procdure 430Microscale Procdure 431

2 Bicyclo[2.2.1]hept-5-ene-endo-2,3-dicarboxylic Acid 431

Miniscale Procedure 431Microscale Procedure 432Hydrolysis of Anhydrides 432Historical Highlight: Discovery of the Diels-Alder Reaction 442

Chapter 13 Kinetic and Thermodynamic Control of a Reaction 445

Thermodynamic Control 448

Kinetic and Thermodynamic Control of a Reaction 450

A Preparation of Cyclohexanone Semicarbazone 451

B Preparation of 2-Furaldehyde Semicarbazone 451

C Reactions of Semicarbazide with Cyclohexanone and 2-Furaldehyde in Phosphate Buffer Solution 451

D Reactions of Semicarbazide with Cyclohexanone and 2-Furaldehyde in Bicarbonate Buffer Solution 452

E Tests of Reversibility of Semicarbazone Formation 452Effect of pH on Kinetic vs Thermodynamic Control 453

Chapter 14 Nucleophilic Aliphatic Substitution: Preparation of Alkyl Halides 461

Reactions 462

Preparation of 1-Bromobutane 467

Miniscale Procedure 467Microscale Procedure 468Analysis of SN Reactions as a Function of Substrate 469

14.5 Preparation of 2-Chloro-2-Methylbutane:

Preparation of 2-Chloro-2-Methylbutane 475

Miniscale Procedure 475Microscale Procedure 476Analysis of SN Reactions as a Function of Substrate 477

Substitution Mechanisms 481

Kinetics of Solvolysis of 2-Chloro-2-Methylbutane 484

Miniscale Procedure 485Effect of Temperature on Rates of Solvolysis 487Effect of Leaving Group on Rates of Solvolysis 487

Chapter 15 Electrophilic Aromatic Substitution 491

Friedel-Crafts Acylation of m-Xylene with Phthalic

Anhydride 505

Miniscale Procedure 505Microscale Procedure 507

Nitration of Bromobenzene 515

A Nitration 515Miniscale Procedure 515Microscale Procedure 516

B Thin-Layer Chromatography 517

C Column Chromatography 518Miniscale Procedure 518

Relative Rates of Electrophilic Aromatic Bromination 525

A Qualitative Measurements 525Miniscale Procedure 525

B Quantitative Measurements 526Miniscale Procedure 526Historical Highlight: Discovery of the Friedel-Crafts Reaction 533

Chapter 16 Oxidation of Alcohols and Carbonyl Compounds 537

Table of Contents xi

B Oxidation of 4-Chlorobenzyl Alcohol to 4-ChlorobenzoicAcid 547

Miniscale Procedure 548Microscale Procedure 549

The Cannizzaro Reaction 553

Base-Catalyzed Oxidation-Reduction of Aldehydes by the Cannizzaro Reaction 555

Miniscale Procedure 555Microscale Procedure 556Historical Highlight: Green Chemistry 560

Chapter 17 Reduction Reactions of Double Bonds: Alkenes, Carbonyl Compounds,

Formation and Reduction of

N-Cinnamylidene-m-nitroaniline 573

Miniscale Procedure 574Microscale Procedure 575

Alcohols 581

Reduction of 9-Fluorenone 582

Miniscale Procedure 582Microscale Procedure 583

Reduction of 4-tert-Butylcyclohexanone 583

Reduction of Benzoin 584

Enzymatic Reduction of Methyl Acetoacetate 588

Miniscale Procedure 588

Determining Optical Purity of Methyl

(S)-(+)-3-Hydroxybutanoate 594

Historical Highlight: Chiral Drugs 596

Chapter 18 Reactions of Carbonyl Compounds 601

Wittig and Horner-Wadsworth-Emmons Reactions 606

A Preparation of (Z)- and (E)-Stilbenes by a Wittig Reaction 606

Miniscale Procedure 606Microscale Procedure 608

Wittig Reaction of 9-Anthraldehyde 609

B Preparation of a Stilbene by the Horner-Wadsworth-Emmons Reaction 610Miniscale Procedure 610

Synthesis of trans,trans-Dibenzylideneacetone 621

Solvent-Free Aldol Condensation 621

Preparation of 4,4-Dimethyl-2-Cyclohexen-1-One 628

Miniscale Procedure 628Microscale Procedure 630Historical Highlight: The Wittig Reaction 636

Chapter 19 Organometallic Chemistry 639

Preparation of Grignard Reagents 643

Miniscale Procedure 644Microscale Procedure 645

Reactions of Grignard Reagents 652

A Preparation of Triphenylmethanol 652Miniscale Procedure 652

Microscale Procedure 653

B Preparation of Benzoic Acid 655Miniscale Procedure 655Exploring the Influence of Mode of Addition 656Microscale Procedure 656

Exploring the Influence of Mode of Addition 658

C Preparation of 2-Methyl-3-heptanol 658Miniscale Procedure 658

Preparation and Characterization of a 3° Alcohol 659Historical Highlight: Grignard and the Beginnings of Modern Organometallic Chemistry 666

Chapter 20 Carboxylic Acids and Their Derivatives 669

Preparation of Benzocaine 673

Miniscale Procedure 673Miniscale Procedure for Microwave Option 674Microscale Procedure 675

20.3 Amides and Insect Repellents 679

Preparation of N,N-Diethyl-m-toluamide 681

Miniscale Procedure 682Microscale Procedure 684

Preparation and Chemiluminescence of Luminol 693

A Preparation of Luminol 693Miniscale Procedure 693Microscale Procedure 694

B Chemiluminescence 694Miniscale Procedure 694Microscale Procedure 695Historical Highlight: Evolution of Synthetic Analgesics 699

Chapter 21 Multistep Organic Synthesis 703

B Preparation of Acetanilide 713Miniscale Procedure 713

C Preparation of 4-Acetamidobenzenesulfonyl Chloride 714

Miniscale Procedure 715

D Preparation of 4-Acetamidobenzenesulfonamide 716Miniscale Procedure 716

E Preparation of Sulfanilamide 717Miniscale Procedure 717

Synthesis of 1-Bromo-3-Chloro-5-Iodobenzene 731

A Preparation of Aniline and Acetanilide 731

B Preparation of 4-Bromoacetanilide 731Miniscale Procedure 732

Microscale Procedure 732

C Preparation of 4-Bromo-2-Chloroacetanilide 733Miniscale Procedure 733

Microscale Procedure 733

D Preparation of 4-Bromo-2-Chloroaniline 734Miniscale Procedure 734

Microscale Procedure 735

E Preparation of 4-Bromo-2-Chloro-6-Iodoaniline 736Miniscale Procedure 736

Microscale Procedure 736

F Preparation of 1-Bromo-3-Chloro-5-Iodobenzene 737Miniscale Procedure 737

Microscale Procedure 738

21.4 Lidocaine: Synthesis of an Anesthetic Agent 747

Synthesis of Lidocaine 751

A Preparation of 2,6-Dimethylaniline 751Miniscale Procedure 751

Microscale Procedure 752

B Preparation of ␣-Chloro-2,6-Dimethylacetanilide 753Miniscale Procedure 753

Microscale Procedure 754

C Preparation of Lidocaine 755Miniscale Procedure 755Microscale Procedure 756Historical Highlight: Discovery of Sulfa Drugs 762

A Removal of the Inhibitor from Commercial Styrene 770

B Polymerization of Pure Styrene 771

C Solution Polymerization of Styrene 771Stability of Polystyrene Toward Organic Solvents 772Polymers and Water 772

Cross-Linking of Polymers 773

Preparation of Nylon-6,10 780

Miniscale Procedure 780Alternative Procedure 781Historical Highlight: Discovery of Polyethylene and Nylon 785

Chapter 23 Carbohydrates 787

Chapter 24 ␣-Amino Acids and Peptides 803

A Preparation of N-tert-Butoxycarbonyl L-Alanine 811Miniscale Procedure 811

D Preparation of Methyl L-Alanylphenyl-L-Alaninate Trifluoroacetate 817

Miniscale Procedure 818Microscale Procedure 818Synthesis of L-Alanyl-L-Phenylalanine 819Historical Highlight: Invention of a Method for Solid-Phase Peptide Synthesis 828

Chapter 25 Identifying Organic Compounds 833

a Pure Compound 835

Elemental Analysis 837

A Sodium Fusion 838Sodium-Lead Alloy Method 838Sodium Metal Method 838

B Qualitative Analysis for Halogens, Sulfur, and Nitrogen 839

Separating Mixtures on the Basis of Solubility 848

Organic Analysis 850

Preparation of Derivatives 856

2,4-Dinitrophenylhydrazine Test for Aldehydes and Ketones 857

Schiff’s Test for Aldehydes 859 Tollens’s Test for Aldehydes 860 Chromic Acid Test for Aldehydes and 1° and 2° Alcohols 861 Iodoform Test 864

Preparation of Semicarbazones 865 Preparation of Oximes 866

25.8 Alkenes and Alkynes 867

Bromine Test for Unsaturation 867 Baeyer Test for Unsaturation 869

Silver Nitrate Test for Alkyl Halides 870 Sodium Iodide Test for Alkyl Chlorides and Bromides 871

Friedel-Crafts Reaction for Detecting Arenes 873 Preparation of Nitroarenes 874

Side-Chain Oxidation of Arenes 875

Lucas Test for Alcohols 878 Preparation of Urethanes 879 Preparation of 3,5-Dinitrobenzoates 880

Bromine Water Test for Phenols 883 Ceric Nitrate Test for Alcohols and Phenols 884 Ferric Chloride Test for Phenols and Enols 884 Preparation of Bromophenols 885

Hydroxylamine Test for Nitriles 901 Hydrolysis of Nitriles 902

Base-Promoted Hydrolysis of Amides 904

Chapter 26 The Literature of Organic Chemistry 905

Index 925

The management and teaching of an introductory laboratory course in organic chemistry is ever-changing, even though the fundamental chemical principles remainthe same Some of the compelling reasons for innovation and change are linked to theincreasing cost associated with purchase and disposal of the chemicals used There isthe added concern of their possible toxicological hazards, both to students and to theenvironment These factors dictate that many experiments be performed on reduced

scales according to procedures commonly termed as miniscale (sometimes called scale) and microscale This edition of our textbook maintains our practice of providing

small-both miniscale and microscale procedures for most experiments This unusual featuregives instructors maximal flexibility in customizing the course for use of apparatusand glassware already on hand and to suit the specific needs of you, the student.The experiments are thoughtfully selected to introduce you to the common labo-ratory practices and techniques of organic chemistry and to illustrate the chemistry

of the wide range of functional groups that are present in organic molecules Someexperiments are designed to familiarize you with the kinetic and thermodynamicprinciples underlying chemical reactions Others allow you to synthesize specificcompounds—some of which are found in nature or are of commercial importance—using reactions that are fundamental to organic synthesis Still others introduce you

to discovery-based and green-chemistry approaches The discovery-based procedures—

there are over 40 of these in the new edition—allow you to develop your own cols for addressing a particular question experimentally, as you might do in aresearch laboratory Discovery experiments are listed inside the front cover and areindicated when they appear in the book with the magnifying glass icon shown in themargin The four procedures involving green chemistry show you how some chemi-cal transformations may be performed using more environmentally friendly proce-dures Green chemistry experiments are indicated when they appear in the book withthe leaf icon shown in the margin Many of the chapters are accompanied by a Historical Highlight, an essay that focuses on interesting topics in organic chemistryand that we believe will broaden your interest in the subject Overall, our hope is thatyour experiences in this course will inspire you to take additional laboratory and lec-ture courses in chemistry, to seize the opportunity to work in a research laboratory as

proto-an undergraduate student, proto-and perhaps even to pursue a career in research

Background Information Our textbook is distinct from many other laboratory manuals because the focused

discussions preceding each Experimental Procedure provide the essential cal and “how-to” background, so other sources need not be consulted in order tounderstand the mechanistic and practical aspects of the specific reactions and procedures being performed These discussions offer the advantage of making the

theoreti-xvii

textbook self-contained, and because they focus on the experiments themselves,they also significantly augment the material found in your lecture textbook.

Experimental Procedures The miniscale approach appeals to instructors who believe in the importance of

per-forming experiments on a scale that allows isolation and characterization of ucts using conventional laboratory glassware The quantities of starting materialsused are usually in the range of 1–3 g, so the costs associated with purchasing anddisposing of the chemicals are modest The amounts of material may be easily han-dled, and it is possible to develop the techniques required to purify the productsand characterize them by comparing their physical properties with those reported

prod-in the scientific literature You will also be able to characterize the startprod-ing als and products by spectroscopic techniques, so that you can see how their spec-tral properties differ In short, you will be able to experience the real world oforganic chemistry in which usable quantities of compounds are synthesized

materi-The microscale approach is especially attractive for minimizing the cost of

purchasing and disposing of chemicals The specialized glassware and otherapparatus required for performing experiments on such small scales is nowreadily available Indeed, many of the components found in a microscale kit arealso found in the advanced organic laboratory, where trained researchers oftenwork with minute amounts of material The amounts of starting materials thatare used in these procedures are often only 100–300 mg Because of the smallquantities of materials being handled, you must be meticulous in order to isolateproducts from microscale reactions Purifying small quantities of materials by dis-tillation or recrystallization is often tedious, so it will frequently be impractical tocharacterize pure products Nevertheless, the experiments performed on themicroscale should provide tangible quantities of material so that you can verifythat the product was formed using chemical tests as well as some spectroscopicand analytical techniques

Organization The experiments we have included are intended to reinforce concepts given in the

lecture course in organic chemistry and to familiarize you with the techniques thatmodern organic chemists routinely use The basic types of apparatus you will needare described in Chapter 2 In addition, videos illustrating the steps required toassemble many of the set-ups are available at the optional Premium Companion

Website at www.cengage.com/login, and we urge you to view these prior to going

to the laboratory In subsequent chapters, we provide figures in the margins of thepages to remind you how the assembled apparatus appears The procedures inChapters 3–6 are designed to introduce you to the different techniques for distilla-tion, liquid-liquid and liquid-solid extraction, and thin-layer, column, and gas-liquid chromatography; the basic principles for these techniques are also described

in their respective chapters The spectroscopic methods that are fundamental toanalyzing organic compounds are described in Chapter 8 Experiments that illus-trate concepts such as selectivity of free-radical substitution (Chapter 9), kineticand thermodynamic control of reactions (Chapter 13), kinetics of nucleophilic sub-stitution reactions (Chapter 14) and electrophilic aromatic substitution reactions(Chapter 15), and the stereochemistry and regiochemistry of addition reactions(Chapters 10, 11, 12, and 17) are intended to provide a better understanding of theseimportant subjects Other experiments illustrate specific chemical transformationssuch as the generation, reactions, and rearrangements of carbocations (Chapters 10and 15), electrophilic aromatic and nucleophilic substitution processes (Chapters

15 and 14, respectively), eliminations (Chapters 10 and 11), oxidations and

reductions (Chapters 16 and 17, respectively), nucleophilic additions to carbonylcompounds and imines (Chapters 17 and 18, respectively), the generation and reac-tions of Grignard reagents (Chapter 19), and the formation of various carboxylicacid derivatives (Chapter 20) An experiment in the latter chapter allows you toobserve the fascinating phenomenon of chemiluminescence The value of enzymesfor effecting enantioselective reactions is illustrated in Chapter 17 Because the cur-rent practice of organic chemistry in industry frequently involves multi-step trans-formations, several examples of multi-step synthesis are contained in Chapter 21.Experiments designed to introduce you to basic concepts of carbohydrate chem-istry and polymer chemistry are provided in Chapters 22 and 23, respectively, andthe experiments given in Chapter 24 give you an opportunity to explore one aspect

of the world of bio-organic chemistry through synthesis of a dipeptide A rationalapproach to solving the structures of unknown compounds with and without theaid of spectroscopic data is given in Chapter 25

Textbook Website This textbook is accompanied by an optional Premium Companion Website where

students can access key material related to the experiments This website providesthe MSDSs and the 1H NMR and IR spectra of the organic reactants and productsfor each experiment, as well as the Pre-Lab Exercises and technique videos Butthere is more to be found there For example, there are tutorials for analyzing 1Hand 13C NMR, IR, and mass spectra, and tables of compounds and derivatives thatare associated with qualitative organic chemistry (Chapter 25) Many laboratorymanuals no longer include “qual organic” because of the availability of spectro-scopic methods; however, we believe that this is a valuable component of the labo-ratory course because it will assist you in developing deductive skills so you candetermine what functional groups are present in a compound whose identity isunknown to you The website also includes links to additional information aboutexperimental techniques, theoretical principles, and famous scientists related toeach chapter The icon for the website, shown in the margin here, alerts you to visit

may be bundled with a new book, or students can purchase Instant Access atwww.ichapters.com with ISBN 0538757140

Spectroscopic Techniques Spectroscopy may be the single most powerful tool for analyzing organic

com-pounds Consequently, thorough discussions of the theory and practical techniquesfor infrared, nuclear magnetic resonance (including 1H and 13C NMR), UV-Vis, andmass spectrometry are presented in Chapter 8 To reinforce the basic spectroscopicprinciples and to provide an opportunity for interpreting spectroscopic data, theinfrared and nuclear magnetic spectra of all of the organic starting materials andproducts are provided in this textbook and at the website associated with it, on the

optional Premium Companion Website at www.cengage.com/login It is also

possi-ble for you to perform simple manipulations of the 1H NMR and IR spectra thatare available at the website For example, you will be able to measure chemicalshifts, integrals, and coupling constants directly on the 1H NMR spectra You willalso be able to determine the position of an absorption in the IR spectrum that isassociated with a specific functional group This “hands-on” experience has proved

an invaluable aid in teaching the basics of interpreting 1H NMR and IR spectra and

is unique to this laboratory textbook

Safety and the Environment Important sections entitled “Safety Alert” and “Wrapping It Up” are included with

each experimental procedure The information in the “Safety Alert” is designed to

w

inform you and your instructor of possible hazards associated with the operationsbeing performed The abbreviated Material Safety Data Sheets (MSDSs) that are

available at the optional Premium Companion Website at www.cengage.com/login

provide additional information regarding flammability and toxicological properties

of the chemicals being used and produced Because of the flammable nature of the

solvents and the chemicals that are handled in the laboratory, the use of flameless

heating is emphasized and should be implemented in order to make the laboratory asafe workplace The guidelines and methods in the “Wrapping It Up” section willfamiliarize you with the proper procedures for disposing of chemicals and other by-products after you have completed the experiment Using these recommendedmethods will help protect the environment and lessen the costs associated with theultimate disposal of these materials

Essays A feature of many of the chapters in the textbook is a Historical Highlight These

essays, some of which are biographical in nature, are designed to familiarize youwith the lives of some of the chemical pioneers who have advanced science Theseaccounts will also provide you with a sense of the excitement and insights of indi-viduals whose scientific observations form the basis for some of the experimentsyou will perform Other essays are intended to relate organic chemistry to youreveryday life We hope they will whet your appetite for the subject of organic chem-istry and enrich your experience as you further develop your scientific expertise

Pre-Lab and Post-Lab Exercises Each experiment is accompanied by two sets of questions The Pre-Lab Exercises are

provided at the optional Premium Companion Website at www.cengage.com/login

and are designed to test your understanding of basic concepts, so you will be able toperform the experiments and techniques safely and successfully Because thesequestions will assist you in preparing for work in the laboratory, we strongly rec-

ommend that you answer them before performing the experiment The Post-Lab

Exercises are found under the heading “Exercises” after each Experimental dure These questions are written to reinforce the principles that are illustrated bythe experiments and to determine whether you understand the observations youhave made and the operations you have performed Furthermore, questions onspectroscopy will help you develop the skills required to interpret IR and 1H and

Proce-13C NMR spectra

Significant Changes from This edition of the textbook includes 14 new discovery experiments and two new

the Fourth Edition green chemistry procedures Three additional Historical Highlight essays are

pro-vided, and many new Web-based references have been added to augment the vitality

of the discussions Furthermore, we have overseen the development and production

of new videos that illustrate how to assemble the apparatus that is required to form the various experimental procedures

per-Feedback As always, we seek your comments, criticisms, and suggestions for improving our

textbook Despite our best efforts, we are certain that there are typographical errorsand the like that have escaped our notice, and we would appreciate your bringingthem to our attention; our e-mail and snail-mail addresses are provided below Nomatter how busy we might be, we shall respond to any messages you send

Instructor’s Manual The Instructor’s Manual is available to adopting instructors on the book’s

pass-word-protected instructor companion website (accessible from www.cengage.com/gilbert) as downloadable Word and PDF files

Acknowledgments As with previous editions, a number of individuals contributed to making this

one a reality These include David Flaxbart (UT Austin), Donvan C Haines (SamHouston State University), Frederick J Heldrich (College of Charleston), DavidJohnson (UT San Antonio), Chad Landrie (UI Chicago), Jason Serin (Glendale Com-munity College), and G Robert Shelton (University of North Texas) Prof M RobertWillcott kindly provided the MRI plots accompanying the Historical Highlight inChapter 8 The capable staff at Cengage Learning provided invaluable support

as we prepared this edition We particularly acknowledge the efforts of RebeccaHeider for her assistance, wise counsel, and diligence, and Sara Arnold for hercareful copyediting of the manuscript We acknowledge the use of 13C NMR spec-tral data from the Spectral Database for Organic Compounds of the JapaneseNational Institute of Advanced Industrial Science and Technology and also AldrichChemical Company, and of mass spectral data from the NIST database We alsothank Bill Vining of SUNY Oneonta and Bill Rohan for developing the Web-basedinformation and John Colapret for conceptualizing and implementing the videosthat accompany our textbook

John C Gilbert

jgilbert@scu.eduDepartment of Chemistry & Biochemistry

Santa Clara UniversitySanta Clara, CA 95053

Stephen F Martin

sfmartin@mail.utexas.eduDepartment of Chemistry & Biochemistry

The University of Texas at Austin

Austin, TX 78712

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Introduction, Record Keeping,

and Laboratory Safety

This chapter sets the stage as you undertake the adventure of experimentalorganic chemistry Although we may be biased, we think that this laboratory experi-ence is one of the most valuable you will have as an undergraduate student There

is much to be learned as you progress from the relatively structured format of yourfirst laboratory course in organic chemistry to the much less defined experimentalprotocols of a scientific research environment The laboratory practices described

in the following sections should serve you well in the journey

1.1 I N T R O D U C T I O N

The laboratory component of a course in organic chemistry has an important role indeveloping and augmenting your understanding of the subject matter The theoreti-cal concepts, functional groups, and reactions presented in the lecture part of thecourse may seem abstract at times, but they are more understandable as a result ofthe experiments you perform The successes, challenges, and, yes, frustrations asso-ciated with the “hands-on” experience gained in the laboratory, as you gather andinterpret data from a variety of reactions, provide a sense of organic chemistry that

is nearly impossible to communicate in formal lectures For example, it is one thing

to be told that the addition of bromine (Br2) across the ␲-bond of most alkenes

is a rapid process at room temperature It is quite another to personally observe

the immediate decoloration of a reddish solution of bromine in dichloromethane

(Br2/CH2Cl2) as a few drops of it are added to cyclohexene The principles oped in the lectures will help you to predict what reaction(s) should occur whenvarious reagents are combined in experimental procedures and to understand themechanistic course of the process(es) Performing reactions allows you to testand verify the principles presented in lecture

devel-Of course, the laboratory experience in organic chemistry has another tant function beyond reinforcing the concepts presented in lecture—to introduceyou to the broad range of techniques and procedures that are important to the suc-cessful practice of experimental organic chemistry You will learn how to handle

impor-a vimpor-ariety of chemicimpor-als simpor-afely impor-and how to mimpor-anipulimpor-ate impor-appimpor-arimpor-atus properly, timpor-alentsthat are critical to your success as a student of the chemical sciences Along with

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videos, Pre-Lab Exercises, and other

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becoming more skilled in the technical aspects of laboratory work, you shouldalso develop a proper scientific approach to executing experiments and interpret-

ing the results By reading and, more importantly, understanding the concepts of

this chapter, you will be better able to achieve these valuable goals

1.2 P R E P A R I N G F O R T H E L A B O R A T O R Y

A common misconception students have about performing experiments is that it ismuch like cooking; that is, you merely follow the directions given—the “recipe”—and the desired product or data will result Such students enter the laboratoryexpecting to follow the experimental procedure in a more or less rote manner Thisunfortunate attitude can lead to inefficiencies, accidents, and minimal educationalbenefit and enjoyment from the laboratory experience

To be sure, cooking is somewhat analogous to performing experiments Thesuccessful scientist, just like a five-star chef, is a careful planner, a diligent worker,

a keen observer, and is fully prepared for failures! Experiments may not workdespite your best efforts, just as a cake may fall even in the hands of a premier pas-try chef

The correct approach to being successful in the laboratory is never to begin any

experiment until you understand its overall purpose and the reasons for each

opera-tion that you are to do This means that you must study, not just read, the entire experiment prior to arriving at the laboratory Rarely, if ever, can you complete the

necessary preparation in five or ten minutes, which means that you should not waituntil just before the laboratory period begins to do the studying, thinking, and writ-

ing that are required Planning how to spend your time in the laboratory is the key

to efficient completion of the required experiments Your performance in the laboratory will benefit enormously from proper advance work, and so will yourgrade!

The specific details of what you should do before coming to the laboratory will

be provided by your instructor However, to help you prepare in advance, we havedeveloped a set of Pre-Lab Exercises for each of the experimental procedures wedescribe These exercises are Web-based and are found at the URL given in the mar-gin; you should bookmark this URL, as you will be visiting it frequently whilepreparing for each experimental procedure In addition, the icon shown in the mar-gin will appear whenever Web-based material is available

Your instructor may require you to submit answers to the Pre-Lab Exercises forapproval before authorizing you to proceed with the assigned experiments Even ifyou are not required to submit the exercises, though, you will find that working

them prior to the laboratory period will be a valuable educational tool to self-assess

your understanding of the experiments to be performed

You undoubtedly will be required to maintain a laboratory notebook, whichwill serve as a complete, accurate, and neat record of the experimental work thatyou do Once more, your instructor will provide an outline of what specific infor-mation should appear in this notebook, but part of what is prescribed will proba-bly necessitate advance preparation, which will further enhance your ability to

complete the experiments successfully The laboratory notebook is a permanent record of your accomplishments in the course, and you should take pride in the

quality and completeness of its contents!

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Chapter 1 ■ Introduction, Record Keeping, and Laboratory Safety 3

1.3 W O R K I N G I N T H E L A B O R A T O R Y

You should be aware that experimental organic chemistry is potentially dangerous,

because many of the chemicals used are toxic and/or highly flammable, and most

of the procedures require the use of glassware that is easily broken Careless dling of these chemicals and sloppy assembly of apparatus are sources of danger

han-not only to you but also to those working near you You should han-not be afraid

of the chemicals and equipment that you will be using, but you should treat them with

the respect and care associated with safe experimental practices To facilitate this,there is an emphasis on the proper handling of chemicals and apparatus through-out the textbook, and the importance of paying particular attention to these sub-

jects cannot be overemphasized In a sense, laboratory safety is analogous to a chain,

which is only as strong as its weakest link: the possibility that an accident will occur

is only as great as the extent to which unsafe practices are followed In other words,

if you and your labmates adhere to proper laboratory procedures, the risk of anaccident will be minimized

It is important that you follow the experimental procedures in this textbookclosely There is a good reason why each operation should be performed as it isdescribed, although that reason may not be immediately obvious to you Just as it

is risky for a novice chef to be overly innovative when following a recipe, it is gerous for a beginning experimentalist to be “creative” when it comes to modify-

dan-ing the protocol that we’ve specified As you gain experience in the organiclaboratory, you may wish to develop alternative procedures for performing a reaction

or purifying a desired product, but always check with your instructor before trying

any modifications

Note that rather detailed experimental procedures are given early in the book, whereas somewhat less detailed instructions are provided later on This isbecause many of the basic laboratory operations will have become familiar to you

text-in time and need not be spelled out It is hoped that this approach to the design ofprocedures will decrease your tendency to think that you are essentially following

a recipe in a cookbook Moreover, many of the experimental procedures given inthe literature of organic chemistry are relatively brief and require the chemist to

“fill in the blanks,” so it is valuable to gain some initial experience in figuring outsome details on your own

Most of your previous experience in a chemistry laboratory has probablyrequired that you measure quantities precisely, using analytical balances, burets,pipets, and other precise measuring devices (Secs 2.5 and 2.6) Indeed, if you havedone quantitative inorganic analysis, you know that it is often necessary to mea-sure weights to the third or fourth decimal place and volumes to at least the first

Experiments in organic chemistry that are performed at the microscale level, that

is, experiments in which less than about 1 mL of the principal reagents is used andthe amounts of solvents are less than 2 or 3 mL, also require relatively precise mea-suring of quantities For example, if you are to use 0.1 g of a reagent and your mea-suring device only allows measuring to the nearest 0.1 g, you could easily have asmuch as about 0.15 g or as little as 0.05 g of the reagent Such deviations from the

desired quantity represent significant percentage errors in measurement and can

result in serious errors in the proportions of reagents involved in the reaction sequently, weights should be accurate to within about 0.01 g and volumes to withinabout 0.1 mL This requires the use of appropriate analytical balances and gradu-ated pipets

Con-Experiments being performed at the miniscale level, which we define as

involving 1–5 g of reagents and usually less than about 25 mL of solvent, normally

do not require such precise measuring Weighing reagents to the nearest tenth of agram is usually satisfactory, as is measuring out liquids in graduated cylinders,which are accurate to ± 10% For example, if you are directed to use 20 mL of diethyl

ether as solvent for a reaction, the volume need not be 20.0 mL In fact, it probably

will make little difference to the success of the reaction whether anywhere from15–25 mL of the solvent is added This is not to say that care need not be exercised

in measuring out the amounts of materials that you use Rather, it means that able time need not be invested in making these measurements highly precise

valu-We’ve inserted markers in the form of stars (★) in many of the experimental

procedures in this textbook These indicate places where the procedure can beinterrupted without affecting the final outcome of the experiment These markersare designed to help you make the most efficient use of your time in the labora-tory For example, you may be able to start a procedure at a point in the periodwhen there is insufficient time to complete it but enough time to be able to workthrough to the location of a star; you can then safely store the reaction mixture

and finish the sequence during the next laboratory period We’ve not inserted stars

at every possible stopping point but only at those where it is not necessarily ous that interruption of the procedure will have no effect on the experimentalresults Consult your instructor if in doubt about whether a proper stopping pointhas been reached

obvi-As noted above, a carefully written notebook and proper safety procedures are

important components of an experimental laboratory course These aspects are cussed further in the following two sections

dis-1.4 T H E L A B O R A T O R Y N O T E B O O K

One of the most important characteristics of successful scientists is the habit ofkeeping a complete and understandable record of the experimental work that hasbeen done Did a precipitate form? Was there a color change during the course ofthe reaction? At what temperature was the reaction performed, and for how longdid the reaction proceed? Was the reaction mixture homogeneous or heteroge-neous? On what date(s) was the work performed? These are observations and datathat may seem insignificant at the time but may later prove critical to the interpre-tation of an experimental result or to the ability of another person to reproduceyour work All of them belong in a properly kept laboratory notebook We makesuggestions for such a document in the following two sections Your instructormay specify other items to be included, but the list we give is representative of agood notebook

1.5 G E N E R A L P R O T O C O L F O R T H E L A B O R A T O R Y N O T E B O O K

1.Use a bound notebook for your permanent laboratory record to minimize the

possibility that pages will be lost If a number has not been printed on eachpage, do so manually Some laboratory notebooks are designed with pairs ofidentically numbered pages so that a carbon copy of all entries can be made.The duplicate page can then be removed and submitted to your instructor or

put in a separate place for safekeeping Many professional scientists use thistype of notebook.

2.Reserve the first page of the notebook for use as a title page, and leave severaladditional pages blank for a Table of Contents

3.Use as the main criterion for what should be entered in the notebook the rulethat the record should be sufficiently complete so that anyone who reads it willknow exactly what you did and will be able to repeat the work in precisely theway you originally did it

4.Record all experimental observations and data in the notebook as they are obtained Include the date and, if appropriate, the time when you did the work.

In a legal sense, the information entered into the notebook at the time of formance constitutes the primary record of the work, and it is important for you

per-to follow this principle Many patent cases have been determined on the basis

of dates and times recorded in a laboratory notebook One such example isdescribed in the Historical Highlight at the end of this chapter

5.Make all entries in ink, and do not delete anything you have written in the

note-book If you make a mistake, cross it out and record the correct information.Using erasers or correction fluid to modify entries in your notebook is unac-ceptable scientific practice!

Do not scribble notes on odd bits of paper with the intention of recordingthe information in your notebook later Such bad habits only lead to problems,since the scraps of paper are easily lost or mixed up They are also inefficient,since transcribing the information to your notebook means that you must write

it a second time This procedure can also result in errors if you miscopy the data.Finally, do not trust your memory with respect to observations that youhave made When the time comes to write down the information, you may haveforgotten a key observation that is critical to the success of the experiment

6.Unless instructed to do otherwise, do not copy detailed experimental

proce-dures that you have already written elsewhere in your notebook; this consumesvaluable time Rather, provide a specific reference to the source of the detailed

procedure and enter a synopsis of the written procedure that contains enough

information that (1) you need not refer to the source while performing the

pro-cedure and (2) another chemist will be able to duplicate what you did For

exam-ple, when performing an experiment from this textbook, give a reference to the

page number on which the procedure appears, and detail any variations made

in the procedure along with the reason(s) for doing so

7.Start the description of each experiment on a new page titled with the name

of the experiment The recording of data and observations from several ferent procedures on the same page can lead to confusion, both for yourselfand for others who may read your notebook

dif-1.6 T Y P E S O F O R G A N I C E X P E R I M E N T S

A N D N O T E B O O K F O R M A T S

There are two general classes of experiments, investigative and preparative, in

this textbook Investigative experiments normally involve making observationsand learning techniques that are common to laboratory work in organic chemistrybut do not entail conversion of one compound into another Some examples are

Chapter 1 ■ Introduction, Record Keeping, and Laboratory Safety 5

solubility tests, distillation, recrystallization, and qualitative organic analysis Incontrast, preparative experiments involve interconversion of different compounds.Most of the procedures described in this textbook fall into the latter category.The format of the laboratory notebook is usually different for these twotypes of experiments Once again, your instructor may have a particular stylethat is recommended, but we provide suggested formats below.

Notebook Format for 1 Heading Use a new page of the notebook to start the entries for the

Investigative Experiments experiment Provide information that includes your name, the date, the title

of the experiment, and a reference to the place in the laboratory textbook orother source where the procedure may be found

2 Introduction Give a brief introduction to the experiment in which you clearly

state the purpose(s) of the procedure This should require no more than fourth of a page

one-3 Summary of MSDS Data As directed by your instructor, either briefly

sum-marize the Material Safety Data Sheet (MSDS) data (Sec 1.10) for the solvents,reagents, and products encountered in the experiment or give a reference towhere a printout of these data is located

4 Synopsis of and Notes on Experimental Procedure—Results Enter a

one-or two-line statement fone-or each part of an experiment Reserve sufficient room

to record results as they are obtained As noted in Section 1.5 of “Notebook

Format for Preparative Experiments,” do not copy the experimental

proce-dure from the textbook, but provide a synopsis of it

Much of this section of the write-up can be completed before coming tothe laboratory, to ensure that you understand the experiment and that you willperform all parts of it

5 Interpretation of Instrumental Data If instructed to do so, discuss any

instrumental data, such as gas-liquid chromatographic analyses and tral data that you have obtained or are provided in the textbook

spec-6 Conclusions Record the conclusions that can be reached, based on the results

you have obtained in the experiment If the procedure has involved ing an unknown compound, summarize your findings in this section

identify-7 Answers to Exercises Enter answers to any exercises for the experiment that

have been assigned from the textbook

A sample write-up of an investigative experiment is given in Figure 1.1

Notebook Format for 1 Heading Use a new page of the notebook to start the entries for the

experi-ment Provide information that includes your name, the date, the title of theexperiment, and a reference to the place in the laboratory textbook or othersource where the procedure may be found

2 Introduction Give a brief introduction to the experiment in which you clearly

state the purpose(s) of the procedure This should require no more than fourth of a page

one-3 Main Reaction(s) and Mechanism(s) Write balanced equations giving the main

reaction(s) for conversion of starting material(s) to product(s) The reason for

balancing the equations is discussed in Part 4 below Whenever possible,

include the detailed mechanisms for the reactions that you have written

Preparative Experiments

1 Your Name

Date

Reference: Experimental Organic Chemistry: A Miniscale and Microscale Approach, 5th ed.

by Gilbert and Martin, Section 6.2

INTRODUCTION

The pigments in green leaves are to be extracted into an organic solvent, and the extract is to be analyzed by layer chromatography (TLC) The presence of multiple spots on the developed TLC plate will indicate that more than a single pigment is contained in the leaves

thin-MSDS DATA

These data are available on the printouts inserted at the back of my lab book

SYNOPSIS OF AND NOTES ON EXPERIMENTAL PROCEDURE—RESULTS

Procedure: Grind five stemless spinach leaves in mortar and pestle with 5 mL of 2:1 pet ether and EtOH Swirl

soln with 3 × 2-mL portions H2O in sep funnel; dry org soln for few min over anhyd Na2SO4 in Erlenmeyer Decant and concentrate soln if not dark-colored Spot 10-cm × 2-cm TLC plate about 1.5 mm from end with dried extract; spot should be less than 2 mm diam Develop plate with CHCl3 Variances and observations:

Procedure followed exactly as described in reference Org soln was dark green in color; aq extracts were

yellowish Half of org layer lost TLC plate had five spots having colors and Rf -values shown on the drawing

below

INTERPRETATION OF INSTRUMENTAL DATA

8.0 Solvent front6.5 cm (orange)

4.7 cm (dark yellow)4.1 cm (lemon yellow)3.4 cm (light yellow)

0.19

No data provided for this experiment

CONCLUSIONS

Based on TLC analysis, the procedure used allows the extraction of at least five different pigments from the

spinach leaves Judging from colors, one of these is a carotene, three are xanthophylls, and the last is

chlorophyll b.

ANSWERS TO EXERCISES

(Answers intentionally omitted.)

Separation of Green Leaf Pigments by TLC

4 Table of Reactants and Products Set up a Table of Reactants and Products as

an aid in summarizing the amounts and properties of reagents and catalystsbeing used and the product(s) being formed Only those reactants, catalysts,and products that appear in the main reaction(s) should be listed in the table;many other reagents may be used in the work-up and purification of the reac-

tion mixture, but these should not be entered in the table.

Your instructor will have specific recommendations about what shouldappear in the table, but the following items are illustrative

a. The name and/or structure of each reactant, catalyst, and product

b. The molar mass of each compound

c. The weight used, in grams, of each reactant and the volume of any liquidreactant We recommend that the weight and/or volume of any catalystsused be entered for purposes of completeness

d. The molar amount of each reactant used; this can be calculated from the

data in Parts b and c.

e. The theoretical mole ratio, expressed in whole numbers, for the reactants

and products; this ratio is determined by the balanced equation for the

reac-tion, as given in Part 3.

f. Physical properties of the reactants and products This entry might includedata such as boiling and/or melting point, density, solubility, color, and odor

g. As directed by your instructor, either briefly summarize the MSDS data(Sec 1.10) for the solvents, reagents, and products encountered in theexperiment or give a reference to where a printout of these data is located

5 Yield Data Compute the maximum possible amount of product that can be formed; this is the theoretical yield This can easily be calculated from the

data in the Table of Reactants and Products as follows First determine which

of the reactants corresponds to the limiting reagent This is the reagent that

is used in the least molar amount relative to what is required theoretically In

other words, the reaction will stop once this reactant is consumed, so itsmolar quantity will define the maximum quantity of product that can be pro-duced From the number of moles of limiting reagent involved and the bal-anced equation for the reaction, determine the theoretical yield, in moles(written as “mol” when used as a unit, as in “g/mol”), of product This valuecan then be converted into the theoretical yield in grams, based on the molarmass of the product

Once the isolation of the desired product(s) has been completed, you

should also calculate the percent yield, which is a convenient way to express the overall efficiency of the reaction This is done by obtaining the actual yield

of product(s) in grams, and then applying the expression in Equation 1.1 erally, the calculated value of percent yield is rounded to the nearest wholenumber As points of reference, most organic chemists consider yields of 90%

Gen-or greater as being “excellent,” and those below 20% as “poGen-or.”

(1.1)

the experimental procedure that contains enough detail so that you do nothave to refer to the textbook repeatedly while performing the experiment

Percent yield ⫽ Actual yield (g)

Theoretical yield (g) ⫻ 100

Chapter 1 ■ Introduction, Record Keeping, and Laboratory Safety 9

Note any variations that you use, as compared to the referenced procedure,and observations that you make while carrying out the formation and isola-tion of the product(s)

that you have isolated in the experiment Appropriate data under this headingmight include boiling and/or melting point, odor, color, and crystalline form, ifthe product is a solid Compare your observations with those available on the

compound in various reference books (for example, the CRC Handbook of istry and Physics or Lange’s Handbook of Chemistry).

leading to undesired products) that are likely to occur in the experiment It isimportant to consider such processes because the by-products that are formedmust be removed by the procedure used to purify the desired product You mayneed to consult your lecture notes and textbook in order to predict what sidereactions might be occurring

meth-ods for preparing the desired compound Such methmeth-ods may involve usingentirely different reagents and reaction conditions Your lecture notes and text-book can serve as valuable resources for providing possible entries for this section

operations that will be used to purify the desired product The chart will show

at what stages of the work-up procedure unchanged starting materials andunwanted by-products are removed By understanding the logic of the purifi-cation process, you will know why each of the various operations specified inthe purification process is performed

Purifying the final product of a reaction can be the most challenging part of

an experimental procedure Professional organic chemists are constantly required

to develop work-up sequences that allow isolation of a pure product, free fromstarting materials and other contaminants They do this by considering the chem-ical and physical properties of both the desired and undesired substances, and it

is important for you to gain experience in devising such schemes as well

instru-mental data, such as gas-liquid chromatographic analyses and spectral datayou have obtained or that are provided in the textbook

have been assigned from the textbook

A detailed example of the write-up for a preparative experiment involving thedehydration of cyclohexanol (Sec 10.3) is given in Figure 1.2 You may not actuallyperform this reaction; nevertheless, you should carefully study the example inorder to see how to prepare specific entries for the first eight items listed The various

entries in Figure 1.2 are labeled with circled, boldface numbers and are discussed

fur-ther in the following paragraphs It is assumed for illustrative purposes that anactual yield of 2.7 g is obtained

1 Use a new page of the notebook to start the entries for the experiment Provideinformation that includes your name, the date, the title of the experiment, and

a reference to the place in the laboratory textbook or other source where theprocedure can be found

1 Your Name

Date 1

Dehydration of Cyclohexanol Reference: Experimental Organic Chemistry: A Miniscale and Microscale Approach, 5th ed.

(Mechanism intentionally omitted.)

Weight Used (g)

Moles Used

Moles Required

Cyclohexanol 100.2 5.2 5 0.05 1 bp 161 °C (760 torr), mp 25.1 °C,

d 0.962 g/mL, colorless

#Entry left blank because this row is for the catalyst

*Entry left blank because this row is for the product

LIMITING REAGENT: Cyclohexanol

Cyclohexene is to be prepared by the acid-catalyzed dehydration of cyclohexanol

Figure 1.2

Sample notebook format for investigative experiments.

Chapter 1 ■ Introduction, Record Keeping, and Laboratory Safety 11

Procedure: Put alcohol in 25-mL rb flask and add H2SO4.Mix, add stirbar, attach to fractional dist apparatus Heat with oil bath; heating rate such that head temp stays below 90 °C Stop when 2.5 mL remain in rxn flask Put distillate in 25-mL Erlenmeyer and add 1–2 g K2CO3.★ Occasionally swirl mix for 15 min and transfer

liquid to 10-mL rb by decantation or pipet Add stirbar and do simple distillation (no flames!); receiver must be close to drip tip of adapter to minimize losses by evaporation Collect product at 80–85 °C (760 torr)

Variances and observations: Procedure followed exactly as described in reference Distillate cloudy throughout

dehydration step; formed two layers in receiver Head temperature never exceeded 77 °C Liquid in stillpot

darkened as reaction proceeded Addition of carbonate (1 g) to distillate caused evolution of a few bubbles of

gas (CO2?) Had to add about 0.5 g more of carbonate to get rid of cloudiness Left solution over drying agent for one week (next lab period) Used pipet to transfer dried liquid to distillation flask Collected cyclohexene in ice-cooled 10-mL rb flask attached to vacuum adapter protected with CaCl2 tube Stopped distillation when

about 1 mL of yellowish liquid remained in stillpot

(Catalyticamount)

bp 80–84 °C (760 torr); colorless liquid; insoluble in water; decolorizes Br2/CH2Cl2 solution and produces

brown precipitate upon treatment with KMnO4/H2O

6.

7.

8.

Figure 1.2 (Continued)

4 2

1

Polymerichydrocarbons

6 5

17

18

20

19

10 FLOW CHART FOR PURIFICATION

(Intentionally omitted.)

12 ANSWERS TO ASSIGNED EXERCISES

(Answers intentionally omitted.)

1, 4 (as potassium

salt), K2SO4 (H2O)x

Figure 1.2 (Continued)