The Complete Idiot’s Guide to Organic Chemistryvi 11 Elimination Reactions—When Atoms Are Voted Off Learn how to get those pesky functional groups off of organic compounds through the m
Trang 1A member of Penguin Group (USA) Inc.
by Ian Guch and Kjirsten Wayman, Ph.D.
Organic
Chemistry
Trang 2www.pdfgrip.com
Trang 3Organic Chemistry
Trang 5A member of Penguin Group (USA) Inc.
by Ian Guch and Kjirsten Wayman, Ph.D.
Organic
Chemistry
Trang 6ALPHA BOOKS
Published by the Penguin Group
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Copyright © 2007 by Ian Guch and Kjirsten Wayman, Ph.D.
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Trang 7Contents at a Glance
A brief overview of organic chemistry and some of the
people who brought it to you.
The story of the covalent bond and how to represent it.
Your handy guide to understanding how to draw the many arrows that are common in organic chemistry.
4 What Organic Molecules Look Like 31
The joys of hybridization, plus a commercial break from
the makers of every molecular model kit.
5 Acids and Bases: Our Corrosive Friends 41
Eat away at your fears of organic chemistry with this
review of our little corrosive friends.
This is where the organic excitement begins Fortunately,
it’s not where it ends!
If the alkanes are considered the parents of organic try, think of the cycloalkanes as organic chemistry’s wacky
chemis-aunt and uncle.
Everything you ever wanted to know (and lots of things you probably didn’t) about multiple bonding but were afraid to ask.
9 Enantiomers, Diastereomers, and Meso, Oh My! 91
Get out the molecular models and learn all about
stereo-chemistry.
Substitution reactions make up a lot of organic chemistry Fortunately, we’ve packaged the important stuff in this
chapter.
Trang 8The Complete Idiot’s Guide to Organic Chemistry
vi
11 Elimination Reactions—When Atoms Are Voted Off
Learn how to get those pesky functional groups off of
organic compounds through the miracle of elimination
reactions.
Part 3: The “Fun” in Functional Groups 127
12 Haloalkanes: Our Halogenated Friends 129
What happens when you put an alkane and halogen atoms
in the same molecule? Find out here!
13 Alcohols: Our Hard-Partying Friends 137
Find out what else alcohol is good for!
14 The Intoxicating Smell of Ethers 149
The story of how ethers can be used for either good (via
chemistry) or evil (via inhalation).
15 The Sweet Bouquet of Aromatic Compounds 159
Okay … these compounds may not smell all that great,
but they sure are good in organic synthesis Find out more about them here!
Though amines smell like rotten fish (at best), they come
in handy for a variety of organic reactions.
17 All About Aldehydes and Ketones 189
Our introduction into the world of the carbonyl group.
The care, feeding, and reactions of molecules with the
–CO 2 H group.
The little brothers and sisters of the carboxylic acids come
out to play Amides, esters, acid anhydrides, and acid
halides as you’ve never seen them before!
How enolates make a wide variety of organic reactions
possible.
21 Introducing the Magical World of Spectroscopy 247
Learn the basics of spectroscopy and find out what it’s
good for.
www.pdfgrip.com
Trang 922 Hot on the Trail of Infrared Spectroscopy 257
How to make and (more importantly) interpret infrared
spectra.
23 NMR—You’ll (Spin) Flip Your Lid! 275
Have you ever wondered how a nuclear magnetic resonance
spectrometer works? If you have (and even if you haven’t),
your questions will be answered here!
24 Carbohydrates: How Sweet It Is! 291
Though they’re sometimes maligned by dieters, we’ll find
out what carbohydrates are and learn about some of their
fascinating and disgusting uses.
25 Amino Acids and Proteins: The Legos
Trang 11What Is Organic Chemistry? 3
What Is Organic Chemistry Good For? 4
Filling the Tank 5
Your Plastic Disco Suit 5
Aspirin: Curing Headaches for Over a Century! 5
Who Invented Organic Chemistry? 6
Early Chemistry 6
The Beginnings of Organic Chemistry 6
Modern Organic Chemistry 7
How to Do Well in Organic Chemistry 7
2 Covalent Bonding 9 Elementary Atomic Structure 10
Chemical Bonding 12
Ionic Bonding: The Jerry Springer Show of Chemistry 13
Covalent Bonding: The Dr Phil of Chemistry 14
Drawing Lewis Structures 15
Polar Bonds 16
Formal Charges 18
Line Drawings 19
3 Pushing Electrons Around 21 Chemistry Is Caused by Moving Electrons 22
What Electrons Want to Do in Neutral Molecules 22
What Electrons Want to Do in Anions 22
What Electrons Want to Do in Cations 23
Moving Electrons Around 23
The Single-Sided Arrow 26
Resonance Structures 27
Drawing Resonance Structures 28
4 What Organic Molecules Look Like 31 An Advertising Interlude 32
sp3 Hybridization 32
Trang 12The Complete Idiot’s Guide to Organic Chemistry
Drawing 3-D Pictures on 2-D Paper 35
sp2 Hybridization 36
sp Hybridization 37
An Easy Way to Determine the Hybridization of an Atom 38
5 Acids and Bases: Our Corrosive Friends 41 Arrhenius Acids and Bases 42
Naming the H3O+ Ion 42
Brønsted-Lowry Acids and Bases 43
How to Measure the Strengths of Brønsted-Lowry Acids 44
Measuring the Strengths of Brønsted-Lowry Bases 47
Factors Affecting Acid Strength 47
Lewis Acids and Bases 49
Part 2: Getting Started 51 6 Alkanes 53 What’s an Alkane? 54
Where Alkanes Come From 54
Naming Alkanes 54
Naming Straight Chain Alkanes 54
Alkyl Groups 55
Degrees of Substitution 57
Putting It All Together to Name Alkanes 57
Constitutional Isomerism 60
Conformations of Alkanes 60
Physical Properties of Alkanes 62
Reactions of Alkanes 63
Combustion of Alkanes 63
Free Radical Halogenation 64
7 Cycloalkanes 65 What’s a Cycloalkane? 66
Naming Cycloalkanes 66
Cis-trans Isomerism in Cycloalkanes 67
Ring Strain 69
The Structure of Cyclohexane 71
Monosubstituted Cyclohexanes 73
Disubstituted Cyclohexanes 74
www.pdfgrip.com
Trang 138 Alkenes and Alkynes 77
What Are Alkenes and Alkynes? 77
Why Do We Care About Alkenes and Alkynes? 78
Naming Alkenes and Alkynes 78
Simple Naming 78
Cis-trans Isomerism in Alkenes 80
E-Z Notation 80
Reactions of Alkenes and Alkynes 82
Hydrohalogenation Reactions 84
Hydration of Alkenes 85
Halogenations 86
Oxidation of Alkenes 88
The Catalytic Hydrogenation of Alkenes 89
9 Enantiomers, Diastereomers, and Meso, Oh My! 91 What Is Stereochemistry? 92
What Makes a Molecule Chiral? 93
Choosing a Name Is Like Clockwork 94
Understanding Diastereomers 96
Examining Meso Compounds 98
Studying Alkene Stereoisomers 99
Step into the Light .99
Comparing the Physical and Chemical Properties of Stereoisomers 100
10 Let’s Get Substituting! 103 SN2 Reactions 103
The Mechanism of S n 2 Reactions 104
Steric Effects 105
Substrate Restrictions 106
Stereochemistry of S N 2 Reactions 107
SN1 Reactions 107
Steric Effects 109
Substrate Restrictions 109
Stereochemistry of S N 1 Reactions 109
So, Which Is It? 110
Solvent Effects 110
Substrate Effects 111
Nucleophile Effects 112
Trang 14The Complete Idiot’s Guide to Organic Chemistry
ii
11 Elimination Reactions—When Atoms Are Voted Off the Island 113
What Are Elimination Reactions? 114
E2 Mechanism of Dehydrohalogenation 116
The E1 Mechanism of Dehydrohalogenation 117
Competition Between Elimination and Substitution Reactions 118
The Strength of the Base/Nucleophile Helps to Determine the Mechanism 119
The Degree of Substitution in the Substrate Helps to Determine the Reaction Mechanism 119
Putting It All Together 122
Anti-Periplanar Elimination Reactions 124
Part 3: The “Fun” in Functional Groups 127 12 Haloalkanes: Our Halogenated Friends 129 What’s a Haloalkane? 130
What Are Haloalkanes Used For? 130
Naming Haloalkanes 131
Forming Haloalkanes 131
Free-Radical Halogenation 132
Hydrohalogenation Reactions 134
Halogenation of Alkenes 135
Reactions of Haloalkanes 135
13 Alcohols: Our Hard‑Partying Friends 137 What Are Alcohols? 138
Naming Alcohols 139
Making Alcohol—It’s Not Just for Moonshiners Anymore! 140
Nucleophilic Substitution of Alkyl Halides 140
Hydration of Alkenes 141
Hydroxylation with OsO 4 141
The Reaction of Carbonyl-Containing Groups with Organometallic Compounds 141
The Reduction of the Carbonyl Group 142
Reactions of Alcohols 142
Formation of Alkoxides 143
Acid-Catalyzed Dehydration 143
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Trang 15Substitution of Alcohols with Hydrogen Halides to Form
Haloalkanes 146
The Oxidation of Alcohols 147
14 The Intoicating Smell of Ethers 149 What Are Ethers? 150
What Are Ethers Good For? 150
How to Name Ethers 150
IUPAC Naming of Ethers 150
Common Names 151
The Names People Actually Use 151
Physical Properties of Ethers 152
The Formation of Ethers 152
Williamson Ether Synthesis 152
Dehydration of Alcohols 153
Formation of Epoxides 154
Reactions of Ethers 154
Autoxidation of Ethers 154
Ring-Opening Reactions of Epoxides 155
15 The Sweet Bouquet of Aromatic Compounds 159 What Are Aromatic Molecules? 160
Naming Aromatic Compounds 160
Monosubstituted Benzenes 161
Disubstituted Benzenes 161
Even More Substituted Benzene Derivatives 162
When Benzene Is the Substituent 163
Molecules with More Than One Aromatic Ring 163
Electrophilic Aromatic Substitution 164
The General Mechanism of Electrophilic Aromatic Substitutions 164
Bromination and Chlorination 165
Nitration 166
Sulfonation 166
Friedel-Crafts Alkylation 166
Friedel-Crafts Acylations 167
Substituent Effects in Electrophilic Aromatic Substitutions 167
Ortho-/Para- Directing and Activating Groups 167
Meta- Directing and Deactivating Groups 169
Trang 16The Complete Idiot’s Guide to Organic Chemistry
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Ortho-/Para- Directing and Deactivating Groups 171
More Than One Substituent 172
16 Amines—the Smell of Victory! 175 What Are Amines? 176
Some General Classes of Amines 176
Naming Amines 177
IUPAC Naming 178
Common Names 179
The Properties of Amines 180
Hydrogen Bonding in Amines 180
Acidity and Basicity in Amines 181
The Synthesis of Amines 182
Alkylation of Ammonia and Amines 182
Gabriel Synthesis of Amines 183
Reduction of Nitrobenzene 183
Reductive Animations 184
Common Reactions of Amines 184
The Formation of Diazonium Salts 184
The Reaction of Aryldiazonium Salts with Hypophosphorous Acid 185
The Decomposition of Aryldiazonium Salts 186
17 All About Aldehydes and Ketones 189 What Are Aldehydes and Ketones? 190
Naming Aldehydes and Ketones 190
Common Naming 191
IUPAC Naming 192
Properties of Aldehydes and Ketones 193
Synthesis of Aldehydes and Ketones 194
Friedel-Crafts Acylation 194
Oxidation of 1° Alcohols to Make Aldehydes 195
Oxidation of 2° Alcohols to Make Ketones 195
Reactions of Aldehydes and Ketones 196
Reaction with Grignard Reagents 196
Reducing Carbonyls to Alkanes 198
The Clemmensen Reduction 198
Wolff-Kishner Reduction 199
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Trang 17The Formation of Acetals 199
Formation of Imines and Enamines 201
Reductive Amination of Carbonyls 202
Reduction of Carbonyls to Alcohols 202
Keto/Enol Tautomerism 203
18 Carboylic Acids 207 What’s a Carboxylic Acid? 207
Naming Carboxylic Acids 208
Common Names for Carboxylic Acids 208
IUPAC Names for Carboxylic Acids 209
Properties of Carboxylic Acids 210
How to Make Carboxylic Acids 211
Reactions of Carboxylic Acids 211
Reducing Carboxylic Acids 212
Fischer Esterification 213
Conversion of Carboxylic Acids to Acid Halides 215
Decarboxylation Reactions 215
19 Carboylic Acid Derivatives 219 Getting to Know the Carboxylic Acid Derivatives 219
Acid Halides 220
Acid Anhydrides 220
Esters 220
Amides 221
Nucleophilic Acyl Substitution 222
Reactions of Carboxylic Acid Derivatives 223
Hydrolysis Reactions 224
Esterification Reactions 225
Formation of Amides 226
Grignard Addition to Esters 226
Reduction Reactions 228
20 The Return of the Enolate 231 Reviewing Keto/Enol Tautomerization 232
The Acidity of α-Carbon Atoms 233
Enolates Are Nucleophiles! 234
The Aldol Reaction 235
Crossed Aldol Reactions 236
Dehydration of β-Hydroxyaldehydes 237
Trang 18The Complete Idiot’s Guide to Organic Chemistry
vi
Aldol-Related Reactions 238
Aldol Reactions with Ketones 238
Claisen Condensations 239
Other Reactions That Involve Fun with Enolates 241
α,β-Unsaturated Carbonyls 241
Part 4: Spectacular Spectroscopy 245 21 Introducing the Magical World of Spectroscopy 247 What Is Spectroscopy? 248
Wavelength, Frequency, and the Speed O’ Light 248
Light and Energy 249
Colors and Energy 250
What Happens When You Add Electromagnetic Radiation to Something? 252
Types of Spectroscopy Used in Organic Chemistry 253
Why Spectroscopy Is Useful 254
22 Hot on the Trail of Infrared Spectroscopy 257 What Is Infrared Radiation? 258
What Are We Measuring, Anyway? 258
What’s in an IR Spectrometer? 259
Introduction to IR Spectra 260
IR Spectra by Functional Group 261
Alkanes 261
Alkenes 261
Alkynes 262
Aromatic Compounds 263
Alcohols 264
Amines 264
Ethers 265
Carbonyl-Containing Compounds 265
A Handy Chart to Make Your Life Easier 268
Figuring Out What You’ve Got 269
23 NMR—You’ll (Spin) Flip Your Lid! 275 What the Heck Is NMR? 275
What Makes the Nuclei Different from One Another? 277
What Does an NMR Spectrum Look Like? 278
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Trang 19Interpreting 1H-NMR Spectra 280
Carbon-13 NMR 284
What a 13 C NMR Spectrum Looks Like 286
13 C NMR Chemical Shifts 287
Part 5: Very Basic Biochemistry 289 24 Carbohydrates: How Sweet It Is! 291 What Are Carbohydrates? 292
Monosaccharides 293
Stereochemistry of Monosaccharides 294
Monosaccharides Get Cyclic 295
Disaccharides 298
Polysaccharides 300
25 Amino Acids and Proteins: The Legos of Biochemistry 303 You Already Know What an Amino Acid Is 304
Meet the Amino Acids 304
“Need to Knows” About the Common Amino Acids 307
Don’t Really “Need to Knows” About the Common Amino Acids 308
Zwitterion! 308
Peptides and Protein 309
Naming Peptides and Proteins 311
Protein Structures 312
Primary (1°) Structure 312
Secondary (2°) Structure 313
Tertiary (3°) Structure 314
Quaternary (4°) Structures 315
Appendies
Trang 21Organic chemistry is scary When you sign up for the class, lots of people tell you
that it was the hardest class that they ever took and that it’s impossible to do well The
first day of class, the professor goes up to the front of the room and draws lots of tle diagrams that he says are molecules but just look like really neat geometric shapes The words your professor uses sound like they mean something, but they are hard to translate into English
lit-The problem with this description is that organic chemistry doesn’t need to be scary Though organic chemistry seems a lot different from your general chemistry class, the concepts are exactly the same except that they are applied to molecules that con-tain carbon As for your friends who told you that organic chemistry is the hardest class ever, keep in mind that the people who complain loudest are usually in the minority Think of all the people who take organic chemistry who aren’t complaining!Now, just because organic chemistry isn’t as bad as you’ve been led to believe doesn’t mean that you can just coast by and collect an excellent grade Like any chemistry class, you’re going to have to spend some time studying and trying to figure out what all of this means Fortunately, you’ve bought this book (which is pretty good, if I do say so myself), which should help you to get through the rough patches
Though it may be immodest to say so, the authors of this book are also exactly the right people to help you learn chemistry I (your main narrarator Ian) am a high school chemistry teacher who is used to explaining scary concepts in easy-to- understand terms My coauthor (Kjirsten) is a college organic chemistry professor who teaches this stuff all the time and knows exactly what your teacher thinks is important Between the two of us and all that prior chemistry knowledge floating around in your brain, you can’t help but become an organic chemistry pro!
The bottom line is this: Relax! You can and will learn organic chemistry!
How This Book Is Organized
We’ve conveniently broken up this book into a few sections:
Part 1, “A Review of General Chemistry,” is meant to refresh your memory about
some of the most important topics from general chemistry that come up in most organic chemistry classes Even if you scored 100 percent on every test you took
in general chemistry, it might not be a bad idea to review this part, just in case you forgot something
Trang 22The Complete Idiot’s Guide to Organic Chemistry
Part 2, “Getting Started,” is an introduction to some of the simplest ideas in
organic chemistry In this part, you’ll learn about the simple organic compounds that provide the basis for the complicated ones you’ll see later You’ll also get to meet the two most important types of organic reactions that you’ll need to know
In Part 3, “The ‘Fun’ in Functional Groups,” you’ll learn about the most
commonly found functional groups that are used in organic chemistry From alcohols
to carboxylic acids to other compounds you’ve never even heard of before, you’ll learn
it all
If you’ve ever wondered how people are able to figure out what chemical compounds
are present in those little flasks, Part 4, “Spectacular Spectroscopy,” will answer
these questions For those of you who like acronyms, here are two fun ones: NMR and IR!
Finally, we’ll wrap up the book with a discussion of very basic biochemistry Because biochemistry is such a complex topic (which is why there are separate classes in
it), we’ve decided to call this part, straightforwardly enough, Part 5, “Very Basic
Biochemistry.”
Special Features and Random Thoughts
Occasionally, I feel the need to share some little tidbit of knowledge with you Depending on the content of this little tidbit, I will put it in one of the following sidebars:
Ideas that you absolutely, positively need to know
The Mole Says
Definitions of complicated words
Practice problems that help you better understand the material covered in each section
You’ve Got Problems
www.pdfgrip.com
Trang 23No book is written without the help of a bunch of people who don’t get their names
on the cover (and usually don’t get paid, either) Though we didn’t feel grateful enough to send them a check, we do want to take the opportunity to thank them for their invaluable help
Both Ian and Kjirsten want to thank the following:
Marcello DiMare, for getting both of us started on our path in organic chemistry Without his patient help and inspiration, we might have become physical chemists, dooming us to a life of differential equations Thanks, Marcello!
Jessica Faust at BookEnds for getting us this book deal, and Mike Sanders at Alpha/Penguin for putting up with our nonsense Although we like to give Mike a hard time (and he seems to like giving us a hard time, too), we’re very grateful for his help and guidance We also want to thank the other folks at Alpha/Penguin who worked behind the scenes to make this book work so well
Our young proofreaders: Sara Rainey, Mingyu Kim, Andrew Dailey, Brittney Lala, Hunter Bohlen, and Erica Tangney Thanks for reading this thing over during your summer vacation so that we wouldn’t have to answer for our dangling participles to the many readers of this book!
And, special thanks to you, the readers, without whom we would not have had the excuse or excitement for writing this book
Ian Guch wants to thank the following folks: To Ingrid, my wife, thanks for making
my life sunny and sweet Melina, thanks for being such an awesome kid! To my parents, brother, grandparents, and rest of my family, thanks for all of your support through the years I also want to thank my friends (you degenerates), everybody I’ve been in a band with over the years (you degenerates), Monsignor Raymond East and
my family at St Teresa of Avila Catholic Church for all their support, and God, to whom all glory and honor are due Most of all, I want to thank my co-author Kjirsten, who is responsible for all of the good parts of the book (The mistakes are mine.)Kjirsten Wayman wants to thank the following: To my parents, family, and friends (who are like my family) for all their love and support in getting me to where I am today Thanks to Tarek Sammakia, my Ph.D advisor, for giving me the skills to understand organic chemistry and being a good role model to teach it Thanks to my supportive colleagues, and especially Joshua Smith for random consultations regard-ing this book Thanks to Humboldt State University for granting me a sabbatical
so I could travel to New Zealand and research the organic compounds from native plant extracts Thanks to the short daylight hours and the endless wind and cold of
Trang 24The Complete Idiot’s Guide to Organic Chemistry
ii
Dunedin, New Zealand, winters for the inspiration to stay inside and work on this book Above all, I want to thank my coauthor Ian, without whose narrative talents and questionable humor this book would not be nearly so exciting
Trademarks
All terms mentioned in this book that are known to be or are suspected of being trademarks or service marks have been appropriately capitalized Alpha Books and Penguin Group (USA) Inc cannot attest to the accuracy of this information Use of
a term in this book should not be regarded as affecting the validity of any trademark
or service mark
www.pdfgrip.com
Trang 25Chemistry
Welcome to organic chemistry! You’re probably thinking that we’re going
to throw a bunch of scary diagrams and formulas at you in the next couple
of pages
Relax! Before we give you all the organic stuff, we want to make sure that you’re comfortable with all of the general chemistry that you (hopefully) learned before taking on the challenge of organic chemistry If you’re
a general chemistry pro, the next few chapters should be an easy stroll through the woods For those of you who may have had trouble in general chemistry, don’t worry, we’ll make sure that you learn everything you need
Trang 27u Organic chemistry defined
u How you use organic chemistry
u The history of organic chemistry
u How you can succeed in organic chemistry
Organic chemistry Even the words sound confusing You already know the
word chemistry and it probably reminds you of time spent in the laboratory,
mixing chemicals together and waiting for something interesting to
hap-pen Organic, on the other hand, brings to mind the grocery store sight of
apples on “sale” for $6 a pound Put them together and what do you get? Experiments on expensive produce? Not quite Let’s find out more …
What Is Organic Chemistry?
Organic chemistry is the study of carbon-containing molecules Most
molecules that contain carbon are called organic; the only exceptions are
Trang 28Part 1: A Review of General Chemistry
4
the oxides of carbon (CO, CO2) and ionic compounds containing the carbonate ion (CO3-2) Organic molecules almost always also contain hydrogen and commonly con-tain oxygen, nitrogen, sulfur, phosphorus, or the halogens
Now, you might think that the reliance on carbon
as the main element might make organic chemistry one of the simplest branches of chemistry to learn Unfortunately, this isn’t the case Much like a puppy that’s eaten all the leftover coffee grounds, carbon atoms like to run around bonding to other carbon atoms, as well as to atoms of other elements As a result, you frequently see carbon forming very long chains of atoms, as well as many-sized rings This flexibility in bonding means that there are an infi-nite number of possible organic compounds that can exist, millions of which are already known That’s pretty good for one element!
What Is Organic Chemistry Good For?
A common question that chemistry students often have is “Why do I have to take organic chemistry, anyway?” It’s only natural to wonder this, particularly given that everybody studying to be a chemist, biologist, or medical worker is stuck taking it You’re probably wondering whether this is just a conspiracy put forth by the chemis-try department to get more funding
Well, Mr (or Ms.) Smart Guy (or Gal), here are three examples of where you already use organic chemistry: gasoline, polyester, and aspirin
Methane, benzene, and
sucrose (from left to
right) demonstrate the
wide variation between
organic molecules.
Foods that are labeled as
“organic” don’t contain any
more or less carbon than other
foods The label “organic” means
something entirely different in this
case, referring to the methods
used to grow the food rather than
the compounds of which the food
is made
Chemistrivia
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Trang 29Filling the Tank
When you go to your local gas station, you probably don’t give much thought to where the gasoline comes from You know it comes from an oil well located in a desert somewhere, ships holding it have the annoying tendency to dump it on seals, and big trucks full of it block traffic when you’re trying to get to work As you might guess, there’s more to the story than this
The crude oil that’s pumped out of the ground is usually much too thick to burn in the gas tank of your car Unlike relatively clear gasoline, crude oil is fairly gummy and dark To make it into a motor fuel, oil refineries “crack” the very large organic molecules in crude oil to make smaller molecules, which are then separated via distil-lation to collect the compounds we normally find in gasoline Molecules too heavy
to be incorporated into gasoline are made into other useful materials, such as fin wax, asphalt, diesel fuel, and motor oils Without organic chemistry, none of this could happen!
paraf-Your Plastic Disco Suit
Everybody loves the shiny look and slick feel of the polyester in a good disco outfit, but hardly anybody thinks about where the polyester comes from Unlike natural fibers, you’ll never see a field full of shiny polyester bushes or a herd of polyester sheep permanently adhered via static electricity to Farmer John’s barn Where does this stuff come from, anyway?
Since the 1950s, the chemical company DuPont (who brought us the slogan “Better living through chemistry”) has brought us better living in the form of polyester and many other plastics As is the case with other polymers, polyester gets its name from
the fact that it contains a chain of many (poly) ester organic groups In addition to
making wide-collared shirts and stretchy pants, polyester is also used to make drink bottles, hoses, and fine carpets It’s truly a wonderful material!
Aspirin: Curing Headaches for Over a Century!
Students in the depths of history had it a lot harder than we do today Not only did they not have Wikipedia handy to answer all of their questions about the world (some
of them correctly!), but they also didn’t have anything to relieve the headaches caused
by staring at their books for hours at a time What was a good student to do?
Trang 30Part 1: A Review of General Chemistry
6
In the middle of the nineteenth century, salicylic acid was extracted from natural sources by, you guessed it, organic chemists This wonder drug was able to cure headaches and fever as if by magic Somewhat less magical was the way that it caused stomach bleeding and severe abdominal pain
Fortunately, the not-so-magical salicylic acid was converted into the truly magical acetylsalicylic acid (the active ingredient in aspirin) in 1897 by the German chemist Felix Hoffmann In the years since, aspirin has been used as a treatment for pain, fever, inflammation, and as a possible treatment for stroke and heart attack—all because of organic chemists!
Who Invented Organic Chemistry?
Right now you’re having one of two thoughts: you’re either convinced that organic chemistry will be lots of fun because it’s so useful, or you’re still annoyed that you have to take organic chemistry and are looking for somebody to blame If you fall into this second category, I have bad news—the people who came up with this died
a really long time ago So that you may properly despise their memories, let’s take a look at the inventors of this noble subject
The Beginnings of Organic Chemistry
With the start of the Enlightenment, people stopped looking at the world in a stitious way and started investigating it through the systematic lens of science It was in this time that organic compounds (called “organic” because it was mistakenly
super-Many of the greatest minds
in history spent time working
as alchemists, including Roger
Bacon, St Thomas Aquinas, and
Isaac Newton
Chemistrivia
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Trang 31thought that they all came from living things) started to be investigated The idea that only living things could make organic molecules was broken with the synthesis
of urea in 1828, a compound found in urine The discovery that organic chemistry could be done in the lab sparked a revolution in the field
Modern Organic Chemistry
Nowadays, organic chemistry is used to make many of the things we take for granted
in our daily lives The plastic wrap with which we wrap our leftovers is a polymer created using organic chemistry The antidepressants we take to keep from strangling our employers are brought to us through the hard work of organic chemists and bio-chemists The Twinkies we use to fill our empty bellies while studying can be stored for centuries though the magic of … you guessed it … organic chemistry
And now, like it or not, you’re an organic chemist, too
How to Do Well in Organic Chemistry
By now, you’re probably saying to yourself, “Hello, Self They make a good case for
studying organic chemistry But can I do it?” Talking to yourself is a sign of insanity,
so maybe we should answer this question
Of course you can pass organic chemistry! There’s nothing magical or mysterious about learning organic chemistry, and we’ve never seen anybody who couldn’t get through their organic chemistry experience, provided that they were willing to work for it To give you a hand, here are some suggestions we strongly recommend you follow to make your organic chemistry experience a successful one:
u Learn the vocabulary! If you want to understand this (or any other) field, you need
to understand the language being spoken All the memorization in the world does you no good if you don’t know what people are asking you!
u Don’t memorize! Instead, learn how things work! When you memorize things,
you’re memorizing specific examples of how things work There’s nothing wrong with this, provided that these are the only examples that you ever come into con-tact with Unfortunately, given the fact that there are millions of known organic compounds, the chances are good that you won’t have memorized the right one
In this book, we’ll be discussing the general ways in which organic molecules behave By learning these methods, you can figure out how any organic molecule will behave under any particular set of conditions rather than being limited to one molecule under one set of conditions
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8
u Slow and steady wins the race! If you’re scheduled to take your organic chemistry
final exam tomorrow, I have bad news for you—you’re doomed! You simply not learn all of organic chemistry in an evening (or even in two evenings) Treat organic chemistry like a 6-foot-long chili dog—digest it in small pieces rather than trying to absorb it all at once
can-u One size doesn’t fit all! When studying organic chemistry, some students have the
tendency to assume that all chemical reactions occur in exactly the same way (which, coincidentally, happens to match whatever you studied that way) Please remember that there’s a reason organic chemistry books are so thick—there’s
a lot to know! If you use common sense and hard work, you’ll be able to figure out how something works
u Don’t let other people scare you! Organic chemistry gets a bad rap for being hard
Everybody has a best friend who “became a philosophy major because they couldn’t pass organic chemistry.” Don’t let this bother you Just because some people have trouble with organic chemistry doesn’t mean you will After all, you’ve got us to guide you through it!
The Least You Need to Know
u Organic chemistry is the study of molecules that contain carbon, with the exceptions of CO2, CO, and carbonates
u Because carbon can bond to form many-sized chains and rings, there are many millions of known organic compounds
u Because so many different parts of our lives use organic chemistry, ing organic chemistry will allow you to better understand the world in which you live
understand-u Organic chemistry has developed from humble roots in alchemy into the reaching experimental science it is today
wide-u You can and will learn organic chemistry
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Trang 33Chapter
Covalent Bonding
In This Chapter
u A review of atoms, electrons, and orbitals
u Ionic and covalent bonding
u Bond polarity
u Several ways of drawing organic compounds
After reading the last chapter, you’re probably all fired up and full of
enthusiasm for learning organic chemistry You’re ready! You’re excited! You’re thrilled at the opportunity to expand your mind! You’re about to burst with excitement!
Hold on there, champ Before we can make you an expert in organic
chemistry, we have to go back and review some of the things you learned
in general chemistry After all, you’re not going to get very far with ments like “oxygen has a higher electron density in the C-O bond due to its relatively high electronegativity when compared to carbon” if you have
state-no idea what any of that stuff means Before you learn the scary phrases that your organic chemistry professor uses, you’ve got to relearn some of the less scary phrases
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10
Elementary Atomic Structure
Author’s note to the reader: this section talks about the simplest part of chemistry, the atom In it, we’ll be talking about what the atom is and how it works We know this is
already very obvious to you, but you’ve got to realize that lots of people who bought this book probably didn’t really understand it all that well the first time This section is for them, not for you
Let’s start off with a topic that everybody is able with: the atom Atoms are the smallest particles
comfort-of an element that still have the properties comfort-of that element As you already know, atoms are made of smaller particles (positively charged protons, neutral neutrons, and negatively charged electrons), but those particles don’t behave the same way as the atoms themselves Atoms cannot be broken apart by chemical means, although nuclear reactions can split them apart
In an atom, the protons and neutrons can be found in the nucleus, while electrons are
found in orbitals surrounding the nucleus Orbitals are regions of space in which you
may find an electron You can think of orbitals as being like a parking lot in front of
a big store—each of the parking spaces is nothing more than a place in which a car may be found Both parking lots and orbitals also tend to fill up in predictable ways;
in parking lots, the spaces closest to the store get filled up most quickly, while spaces further away are filled last In the same way, orbitals with lower energies are filled more quickly than those with higher energies Some caution should be exercised in using this analogy, because while it’s possible to put two electrons in one orbital, attempting this with cars in a parking lot is probably unwise
Orbitals come in several different shapes, depending on the type of orbital The ones that you’ll be working with most in organic chemistry are the s-orbitals and p-orbitals, shown here
Even if you did really well
in general chemistry, don’t
skip the next few chapters Let’s
be honest, you’ve probably for
gotten a lot of this stuff and need
a refresher Believe us, you’ll be
glad you reviewed this stuff!
Bad Reactions
Atoms are the smallest pieces of elements that still have the properties of that element (as opposed to protons, neutrons, and electrons, which don’t) They cannot be broken apart during chemical reactions
Orbitals are regions of space surrounding the nucleus of an atom where electrons can
be found A maximum of two electrons can be placed in each orbital
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Trang 35The first energy level contains one s-orbital The second energy level contains one s-orbital and three p-orbitals The third energy level contains one s-orbital, three p-orbitals, and five d-orbitals The locations of the electrons in an atom can be repre-sented with something called an “electron configuration.”
Electron configurations are determined using the following rules:
u Electrons always occupy lower energy orbitals before they occupy higher energy orbitals Orbitals are represented by horizontal lines, and electrons are repre-sented by vertical arrows (↑ or ↓)
u A maximum of two electrons can occupy a single orbital When two electrons are in an orbital, we tell them apart by showing them with opposite spins, repre-sented by arrows that point in different directions (↑↓)
u If more than one orbital of equal energy is available, put one electron in each orbital with parallel spins until all of them are half full Only once they are all half full can you start putting another electron in each orbital
We can see how this works using the example of oxygen, which has eight electrons
You can see that the lower energy orbitals are filled completely and that the 2p-orbitals have the last four electrons in them In accordance with the third rule, the first three electrons filling the 2p-orbitals are drawn in separate orbitals—it’s only when we run out of 2p-orbitals that we start doubling up the electrons by adding a second arrow
There are one s-orbital and three p-orbitals in an energy level.
The electron configuration of oxygen.
Problem 1: Draw the electron configuration of nitrogen
You’ve Got Problems
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12
Though electron configurations are handy for showing the types of orbitals where all the electrons in an atom can be found, there are much better ways to spend your time than drawing big bunches of lines with arrows in them Fortunately for us, not all of the electrons in an atom are involved with forming chemical bonds—only the
outer electrons really get involved with doing istry These electrons are so handy that we give them
chem-a specichem-al nchem-ame: vchem-alence electrons.
In organic chemistry, it’s usually only the outermost s- and p-electrons that we need to worry about We can handily draw these electrons around an atom using Lewis dot structures, which show the valence electrons arranged around the four sides of an atom (as seen in the following figure)
Chemical Bonding
Whew! We’ve finally finished talking about the atom Unfortunately, you may have already noticed that chemistry frequently requires you to keep track of more than one atom at a time As a result, we’ve got to figure out how atoms combine with one another to form chemical compounds
Valence electrons are the outer
most electrons in an atom and
are responsible for chemical
bonding and reactions
The Lewis dot structure for oxygen As is the case with the electron ration, you can see that two of the outermost orbitals are totally filled and the remaining two are only half filled.
Lewis dot structures are named after the physical chemist Gilbert Lewis (1875–1946)
In addition to coming up with the idea of dot structures, he did pioneering work involving chemical bonding, relativity, acids and bases, chemical equilibria, and thermodynamics
Chemistrivia
Problem 2: Draw the Lewis dot structure of carbon
You’ve Got Problems
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Trang 37As you may recall from general chemistry, noble gas elements (group 18 on the odic table) are almost completely nonreactive This is because they have a completely filled outer energy level Because their outermost energy level is completely filled, there is no real reason for them to undergo chemical reactions They’re stable! Other elements, on the other hand, don’t have completely filled outermost energy levels As
peri-a result, they wperi-ant to either gperi-ain or lose electrons to get peri-a filled outer energy level
like the noble gases This tendency is enshrined in the octet rule.
Octet rule: In bonding, all elements gain, lose, or share electrons so they end
up with the electron configuration of their nearest noble gas
Metals generally need to lose electrons to
be like the nearest noble gas Sodium, for
example, has only one more electron than
neon, so it’s easier for sodium to lose one
electron than it is for it to gain seven to
become like argon Chlorine, on the other
hand, needs to gain only one electron to be
like argon, whereas it would have to lose
seven electrons to be like neon Elements
that want to gain electrons from other
atoms are said to have a high
electronegativ-ity, while those that want to lose electrons
are said to have a low electronegativity
Ionic Bonding: The Jerry Springer Show of Chemistry
If you watch The Jerry Springer Show (and I know you do), you’ve noticed that the
guests generally seem to have relationship problems Why, just this morning this toothless guy was complaining that he didn’t feel comfortable telling his wife that he
Chemistry professors frequently get annoyed when you say that “nitrogen wants
to …” in reference to a chemical reaction Many will rightly tell you that atoms aren’t little people and don’t have any particular desires to do anything at all During the course of this book, when I say that an atom “wants to do [something],” what I really mean is “the atoms will be more stable when they do [something].”
Bad Reactions
Electronegativity is a measure
of the tendency of an element to gain electrons to be like its nearest noble gas Nonmetals (on the right side of the periodic table) tend to have high electronegativities, while metals (on the left side
of the periodic table) have low electronegativities
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liked to wear her clothes when she wasn’t around and that this was hurting their tionship It turns out that when the wife came out, she was actually relieved and felt that, if giving her clothes to him would make him happy, it would make her happy and strengthen their relationship All was well until an audience member commented that the woman “had a rat face,” whereupon chaos, again, took over
rela-Ionic compounds, believe it or not, are formed by a not totally dissimilar situation When an atom with low electronegativity (usually a metal) comes into contact with
an atom with high electronegativity (usually a nonmetal), the less electronegative atom gives its electrons to the more electronegative atom The result of this is that the first atom now has a positive charge (a “cation”) and the other has a negative charge (an “anion”), causing them to be electrostatically attracted to one another and form an ionic compound An example of this occurs when lithium combines with fluorine to form lithium fluoride
Covalent Bonding: The Dr Phil of Chemistry
Covalent bonding, on the other hand, is more like an episode of Dr Phil On today’s
Dr Phil, a couple came in for help because their child was acting like a moron
(though they phrased it better than that) Predictably, after Dr Phil worked with the couple (using his signature combination of ridicule and shame), the couple realized that love and mutual support would allow them to work through the situation and give them all happy new lives together The audience even said “Awwww” at one point, so you know it worked
Covalent bonding is similar to this When two electronegative elements come into contact with each other, there is no transfer of electrons because both elements need
to gain electrons Much like today’s episode of Dr Phil, both atoms have to work
together to get what they want In this case, they need to share electrons—the shared
electrons count toward both of the atoms that are bonding Such a bond, caused by a
shared pair of valence electrons, is called a covalent bond This is what occurs when two fluorine atoms bond with one another
When a lithium atom and a fluorine atom combine, the lithium atom transfers its outer electron to fluorine, resulting in the formation of an ionic compound.
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Trang 39If more than one electron from each atom needs to be shared so that both atoms can get a full energy level, more than one covalent bond can be formed Such is the case when two oxygen atoms react with one another to form O2.
Drawing Lewis Structures
For the previous examples, we can see that drawing these molecules isn’t very ficult However, as the molecules get bigger, drawing all of these dots becomes something of a chore As a result, it’s easier to show covalent bonds as being lines between the bonded atoms rather than as being pairs of dots Let’s redraw our exam-ples from before
dif-For larger molecules, it’s sometimes a little challenging to figure out how all the atoms will fit together from a chemical formula Fortunately, here are some general guidelines to help you out with drawing larger organic molecules:
u Hydrogen atoms and halogens form one bond
u Oxygen’s family forms two bonds in neutral molecules—one bond when they have a negative charge, and three bonds when they have a positive charge
u Nitrogen’s family forms three bonds in neutral molecules—two bonds when they have a negative charge, and four bonds when they have a positive charge
Two neutral fluorine atoms must each share one unpaired electron so that they can both be like the nearest noble gas.
By combining more than one unpaired electron at a time, a double bond is formed and both oxygen atoms end up with filled energy levels.
Just replace the bonding pairs of electrons with lines and you’re done!
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u Carbon almost always forms four bonds Carbon atoms also seem to like to bond
to form chains, so unless you have a compelling reason for doing otherwise, bond carbon atoms to other carbon atoms On the rare occasion that carbon is charged, it forms three bonds whether it has a negative or positive charge.And that’s it! If you can follow these rules, you can usually figure out what a molecule looks like Let’s give it a shot with methanol, CH3OH
Typically, organic chemists give you a hand with how they write the formulas of organic molecules When you see “CH3OH,” realize that it’s written that way for a reason In this case, the formula should indicate to you that three hydrogen atoms are bonded to the carbon atom and that oxygen is bonded to hydrogen The following gives you a partial drawing
From here, it’s just a matter of combining the two pieces to end up with a molecule that follows the rules I gave you In this example, you can see that the carbon atom is bonded only three times and that the oxygen atom is bonded only once To get them both bonded the proper number of times (four and two times, respectively), we can bond them to each other, resulting in the following
Polar Bonds
So far, we’ve treated covalent bonds as if both atoms shared their electrons perfectly
Unfortunately, as is also often the case on Dr Phil, both sides don’t always like to
share
The way that the formula of CH 3 OH
is written should tell you that the
molecule contains these two pieces.
The exciting conclusion of our Lewis