Chemistry part 17, Julia Burdge,2e (2009) pps

form when molecules with two different functional groups combine, with the elimination of a small molecule, often water.. An amino acid has both the carboxylic acid functional group and

396 CHAPTER 10 Organic Chemistry

The number 66 refers to the fad that there are

s i x C atoms in each monomer Other nylons,

such as nylon 610, are made from various

combinations of molecu l es similar to adipic ac i d

and hexamethylenediamine

6 Each step lengthens the chain of carbon atoms and results in the formation of a new

radical, continuing the propagation of the reaction Reactions such as this are known as

chain reactions They continue until the system runs out of ethylene molecules or until the radical species encounters another radical species resulting in termination of the reaction

form when molecules with two different functional groups combine, with the elimination of a

small molecule, often water Many condensation polymers are copolymers, meaning that they are made of two or more different monomers

SECTION 10.6 Organic Polymers 397

C / \

plastic wrap

Packing

material,

insulation, furniture

Nylon was first made by Wallace Carothers2 at DuPont in 1931 The versatility of nylons is so great

that the annual production of nylons and related substances now amounts to several billion pounds

Biological Polymers

Naturally occurring polymers include proteins, polysaccharides, and nucleic acids

Proteins, polymers of amino acids, play an important role in nearly all biological processes The human body contains an estimated 100,000 different kinds of proteins, each of which has a specific

physiological function An amino acid has both the carboxylic acid functional group and the amino

functional group Amino acids are joined together into chains when a condensation reaction occurs

between a carboxy group on one molecule and an amino group on another molecule (Figure 10.13)

2 Wallace H Caro th e r s (1896 1937) American chemi s t Be s ides it s enomlO U S commerci a l s ucce ss Carothers's work on

nylon i s ranked with that of Staudinger in clearly elucidating macromolecu lar s tructure and properti es D e pre s sed by the death

of his s i s ter and wrong l y believing that his life' s work had been a fai lur e , Carother s committed s uicide at the age of 41

Figure 10.12 (a) Condensation reaction between an alcohol and a

carboxy li e ac id to form an ester

(b ) Condensation of two alcohol molecules in the pre sence of s ulfuric

acid t o form an ether

398 CHAPTER 10 Organic Chemistr y

Figure 10 13 Format ion of a

peptide bond with elimination of wate r

Figure 10 14 The 20 amino acids

essential to li v ing organisms The

shaded area repre se nt s the R group

SECTION 10.6 Organic Polymers 399

The bonds that form between amino acids are called peptide bonds Very long chains of amino acids assembled in this way are called protein s, while shorter chains are called polypeptides

Amino acids consist of a central carbon atom bonded to four different groups: an amino

group, a carboxy group, a hydrogen atom, and an additional group (highlighted in Figure 10.14)

consisting of carbon, hydrogen, and sometimes other elements such as nitrogen or sulfur Proteins

P e ptid e bonds are a l so calle d ami d e bonds or

amide link a ges beca use they conta i n the am i de

functional group

400 CHAPTER 10 Organic Chemistry

Polysaccharides are polymers of sugars such as glucose and fructose Starch and cellulose are two polymers of glucose with slightly different linkages and very different properties In

starch, glucose molecules are connected by what biochemists call ~ linkages This enables mals, including humans, to digest the starch in such foods as corn, wheat, potatoes, and rice

ani-Starch

In cellulose, the glucose molecules are connected by ex linkages Digestion of cellulose requires

enzymes that most animals do not have Species that do digest cellulose, such as termites and ruminants (including cattle, sheep, and llamas), do so with the help of enzyme-producing symbi-

otic bacteria in the gut

OH

Nucleic acids, which are polymers of nucleotides, play an important role in protein

syn-thesis There are two types of nucleic acids: deoxyribonucleic acid (DNA) and ribonucleic acid

(RNA) Each nucleotide in a nucleic acid consists of a purine or pyrimidine base, a furanose sugar

(deoxyribose for DNA; ribose for RNA), and a phosphate group Figure 10.15 shows the building blocks of DNA and RNA The components of a nucleotide are linked together as shown in Figure 10.16 These molecules are among the largest known-they can have molar masses of up to tens

of billions of grams RNA molecules, on the other hand, typically have molar masses on the order

of tens of thousands of grams Despite their sizes, the composition of nucleic acids is relatively

simple compared with proteins Proteins consist of up to 20 different amino acids, whereas DNA and RNA consist of only four different nucleotides each

Found only in DNA Fonnd in both DNA and RNA

D eoxy rib ose unit

Figure 10.16 Struc t ure of a nucleotide , one of the repeating unit s in DNA

SECTION 10 6 O r gani c Po ly m ers 401

Fonnd only in RNA

4 0 2 CHAPTER 10 Organic C hemistry

Applying What You've Learned

Edu-c ati o n and Pres c ribin g Safety (STEPS) program In order for physicians to prescribe

Problems:

CHAPTER SUMMARY

Section 10.1

o Aromatic compounds contain one or more benze ne ring s Aliphatic

compounds are organic compounds that do not contain benzene ring s

o Alkyl groups consist of just carbon and hydrogen They are deri ve d

Common functional groups and their formulas include

Amide RCONH2, RCONHR ', or RCONR ' R "

o Many organic compounds contain more than one functional group A

substituent in an alkane is a group other than h y drogen that is bonded

to the carbon chain

o An amino acid contains both the carboxy group and the amino group

o Condensed structural formulas or condensed structures abbreviate

a series of repeating units , such as -CH2CH2CH2CH2- , into a more

Skeletal structures use straight line s to represent C-C bond s The y

of emphasizing a particular functional group H atom s are not show n

in skeletal structures-again, except to emphasize a fun c tional group

Section 10.4

o Constitutional isomers are molecules in which the s ame atoms are

Isomers

o Molecules that are non s uperimpo s able mirror image s of each other are

optical isomers They are al so refen'ed to as chiral, and each of the

are opposite each other An equal mixture of both enantiomers is

called a racemic mixture A racemic mixture does not rotate the plane

Section 10.5

o An electrophile generally i s a positively charged ion that is attracted

to electrons A nUcleophile is a negati v ely charged ion or a partially

o A carbocation is an in te rmediate s pecies in which one of the carbon

atoms i s s urrounded b y only s ix electron s and bears a positive charge

o

o

0

0

Electrophilic addition reactions and nucleophilic addition reactions

involve the addition of a molecule or an ion to another molecule

Substitution reactions occur when an electrophile replaces a hydrogen

a carbon atom

Carbocations are the intermediate species in racemization, a

nucleophilic substitution reaction in which a single enantiomer is

con v erted into a racemic mixture

An elimination reaction is one in which a double bond forms and a

•

o Hydration is the addition of a water molecule across a double bond

o Isomerization reactions convert one isomer into another

Section 10.6

o Polymers are long chains of repeating molecular units called

monomers Polysaccharides are polymers of sugars Addition

polymers form when a radical s pecie s attacks a double bond, forming

on

reaction Condensation polymers form when molecules with two

different functional groups undergo a condensation reaction

o Copolymers are polymers that contain more than one type of

monomer

o Proteins and polypeptides are biological polymer s in which the

monomers are amino acids Amino acids are joined by peptide bonds,

wh i c h result from the condensation reaction between the amino group

of one amino acid and t he carboxyl group of another amino acid

o Nucleic acids are poly mer s of nucleotides The two types of nucleic

acid are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA)

Each nucleotide in a nucleic acid consists of a purine or pyrimidine

base, a furanose s ugar (deoxyribose for DNA; ribose for RNA), and a

phosphate group linked together

404 CHAPTER 10 Organic Chemistry

Conden sa tion reaction, 396

Ge ometr ical isomer, 382

Heter oatom, 377

Hydration, 391 Condensed s tructural formula, 376 Isomeri za tion reaction , 394 Condensed structure, 376 Kekule s tru c ture , 376

Constitutional i some ri s m , 382 Ketone , 370 Copolymer, 396 Monomer, 395

Deox y ribonucleic acid (DNA), 400 Nucleic acid, 400 Electrophile, 386 Nucleophile, 386

Electrophilic add ition, 387 Nucleophilic addition, 388

Eliminati o n reaction , 394 Nucleotide, 400 Enantiomer , 383

Ester, 370

Optical i so mers, 383

Peptide bond, 399

QUESTIONS AND PROBLEMS

Section 10.1: Why Carbon Is Different

Trans, 382

Explain why carbon i s able to form so many more compounds

than any other element

10.2 Why was Wohler 's sy nthe s i s of urea so imp o rtant for th e

development of organic c hemi s try?

10 8 Draw s tructure s for molecule s with the following form ula s:

lOA What are functional groups? Why is it logical and useful to

classify organic compounds according to their functional group s?

10.5 Draw the Lewi s structure for each of the following functional

groups: alcohol, aldehyde, ketone, carboxylic acid, amine

10.6 Name the cla ss es to which the fo llo wing compounds belong:

10.7 Clas s ify each of the following molecule s as alcohol, aldeh y de ,

ketone , carboxylic acid, or amine:

10.11 Give the name of the alkane represented by the model shown

10.13 Write st ructural formula s for each of the following based on their

systematic names The name s quoted in parenthe s es are so -called

structure

(a) 2,2,4-Trimethylpentane ("isoocta ne ")

(b) 3-Methyl-1-butanol ("isoamyl alcohol ")

(d) 2,2,2- Trichloroethanal ("chlora l" )

(a) 3,3-Dimethyl-2-butanone ("pi nacolone ")

10.15

10.16

(b) 3-Hydroxybutanal ("ace taldol")

(c) Ethyl penta no ate ("et h y l va lerate ")

(d) 6-Methy 1- 2- heptanarnine ("isooc t y larnine ")

Classify the oxygen-containing groups in the plant hormone

10.17 PABA was the active UV-absorbing compound in earlier versions

of sunblock creams What f unctional groups are pre sen t in

10.18 Lidocaine (C'4H22N20) is a widely u s ed local anesthetic Classify

Section 10.3: Representing Organic Molecules

Problems

10.19 Write str uctural formulas for the following organic

compounds: (a) 3-methylhexane, (b) 2,3-dimethylpentane,

(c) 2-bromo-4-phenylpentane, (d) 3,4,S-trimethyloctane

10.20 Write structural formulas for the following compounds:

(a) 1, 1,3-trichloro-2-propanol, (b) 3-methyl-3-pentanamine,

(c) 3-bromo-l-chloro-2-butanone, (d) propyl-4-bromobutanoate

to a skeletal ( line ) s tructure

10.22

( b) Convert the following to a condensed structure and to a

( a) Convert (CH 3 )2C =CHC02H to a Kekule s tructure and to a

( b ) Convert the following to a condensed structure and to a skeleta l ( line ) s tructure:

4 0 6 CHAPTER 10 Organic Chemistry

10.23

10.24

10.25

fruit s

i s largely respon s ible for the

(a)

(b)

(c)

intermediate in glycoly s i s , the proce s s

C6HI3NOz: Isoleucine, one of the 20

I

OH

(b)

10.26 Given a structural formula or skeletal (line) structure, rewrite it in

the other style

° ( c )

I

H

°

10.27 U s in g the curved arrow s a s a guide to placing the electron s,

10.28 U s ing the cur v ed an'ow s a s a guide to placing the e lectron s,

10.29 U s e curved arrow s to s how how the re s onance s tructure on the

U s e c urved arrows to show how the re s ona n ce s tructure on the

left can be tran s formed to the one on the right

10.31 Alkenes exhibit geometrical isom e ri sm becau s e rotation about

the C=C bond is re s tricted Explain

10.32 W h y is it that a lkan es and alkynes, unlike alkene s, have n o

geometrical i so mers?

10.33

10.34

10.35

Define the term chiral What are enantiomers?

W h at factor determines whether a car bon atom in a compound i s chira l ?

Fill in the blanks in the given paragr ap h with the most appropriate term from the following: chiral, cis, constitutional

isomers, enantiomers, re s onance str ucture s, stereoisomers , trans

I some rs are different compou nd s that have the s ame mol ec u l ar formula I so mer s that ha ve their atoms connected in a different order (branched versus unbranched c hain, for example ) or a

different sequence of bond types (C=CCC versus CC=CC, for exampl e) are termed Isomer s with the

sa me order of connection s and seq uence of bond types, but whic h differ in the s patial arrangement of the atoms are called

_ _ _ _ _ _ _ Thi s i s often seen in compounds where substituents may be on the sa me or oppos ite s ide s of a

carbon-carbon double bond Sub s tituent s on the s ame s ide are described as _ _ _ _ _ _ _ ; tho s e on oppo s ite sides are

_ _ _ _ _ _ _ A different kind of i so meri s m characteri z es a _ _ _ _ _ _ _ molecule; that i s, a molecule wit h a s tructure that a llo ws for two non s uperimpo s able mirror - image f orms Two

nonsuperimpo sa ble mirror images are of the other

10.36 Write structura l formu l as for all the C 5 H lO alkene s, and identify

the relationship (co n stitutional isomer or stereoisomer) of each

o n e to the others Are any chiral?

Problems

10.3 7 Draw all po ssi ble structural isomer s for the following alkane:

10.38 Draw a ll po s sible isomer s for the molecule C4H g

10.40 Which of the following amino acid s are chiral:

(a) CH3CH(NH2)COOH, (b) CH2( NH2) COOH , (c) CH2(OH)CH(NH2) COOH?

the formula C7H7C l All i so mers contain one benzene ring

10.42 Draw a ll t h e str uctural i so mers of compound s wit h the formula

C4HgCI2 Indicate which i so mers are chiral, and give them systemat i c names

,

QUESTIONS AND PROBLEMS 407

H

(b)

10.44 Suppo s e b enzene contained three distinct s in gle bond s and three

distinct double bonds How many different isomers wo uld there

be for dichlorobenzene (C6H4C I2)? Draw all your proposed

How many asymmet ric carbon atom s are pre sen t in eac h of the

following compo und s?

u s ing we dg es and da s he s to s how s tereochemi s try

(a)

( b )

(c) "' ",

( d )

408 CHAPTER 10 O rgan i c Chemistry

Section 10.5: Organic Reactions

R eview Questio ns

10.52

(b) The compound 1 ,2 -dibromoethane (BrC H2CH2Br ) wa s

(c) Certain reactions of aldehydes and ketones begin with

contain an -OH group attached to a carbon-carbon double

[ (CH3hC=0] to its enol i s omer

environment by reactions catalyzed by dehalogenase enzymes

with nucleophilic substitution involving a carboxylate site of the

A common reaction in carbohydrate biochemistry is the

conversion of an aldose to a ketose T h e glucose to fructose

general case:

H •

En zy mes facilitate the reaction, but for s implicity the overall

step in the mechani s m and use curved arrows to track electron flow

I

C I