Kelter P., Mosher M., Scott A. Chemistry. The Practical Science

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518 Chapter 12 Carbon

Structures and Uses of Selected Alcohols

Common Name Lewis Structure 3-D Ball-and-Stick Structure Selected Uses

Methanol Fuel, fuel additive

Rubbing alcohol

Phenol

Found in cosmetics and

foods

1,2,3-Propanetriol

(glycerol)

Antifreeze, de-icing

agent

1,2-Ethanediol

(ethylene glycol)

Solvent in chemical

synthesis

2-Methyl-2-propanol

(tertiary butyl alcohol)

2-Propanol

(isopropyl alcohol)

TABLE 12.8

H H

Making resins (viscous

substances often used as

adhesives) for use in

plywood manufacture

and automotive

applications

12.10 From Alcohols to Aldehydes, Ketones, and Carboxylic Acids 519

Note that this reaction is similar to the dehydrogenation reactions of the alkanes.

As another example, ethanol can be oxidized to ethanal. Ethanal, also known as

acetaldehyde, is used primarily in the production of polymers (Section 12.12)

and medicines.

An aldehyde is named by taking the name of the alcohol from which it is de-

rived and replacing the ending -ol with -al. No number is needed as part of the

name to indicate where the aldehyde group occurs in the compound, because it

always occurs at the end of a carbon chain.

The hydroxyl group of secondary alcohols can be oxidized to a carbonyl

group. In this case, compounds called

ketones are formed. Ketones differ from

aldehydes in that they have two carbon atoms bonded to the carbonyl carbon

atom. For example, 2-propanol can be oxidized to propanone (acetone).

Propanone is an excellent solvent because of its ability to dissolve both polar

and nonpolar molecules. It has a low boiling point and a low toxicity, ﬁnding use

as a solvent for paints and as a ﬁngernail polish remover. For these reasons, over

3 billion kilograms of propanone are used each year in industry.

Tertiary alcohols do not react with oxidizers to make carbonyl compounds.

For instance, there is no reaction when we attempt to oxidize 2-methyl-2-

propanol under the conditions typical for primary and secondary alcohols. This

lack of reactivity occurs because the carbon bearing the —OH group does not

have a hydrogen that can be removed to make the carbonyl (CPO).

Aldehydes have a characteristic biting and often unpleasant aroma. Ketones,

on the other hand, have an aroma that is not so unpleasant, but more medicinal.

Chemically, though, the important difference between aldehydes and ketones is

that the aldehydes can be oxidized further to form

carboxylic acids. The carboxylic

acids carry the

carboxyl functional group, the combination of a carbonyl and a

hydroxyl group. Ethanal, for example, can be easily oxidized to ethanoic acid.

Oxidation

Ethanal Ethanoic acid

Oxidation

No reaction

2-Methyl-2-propanol

Oxidation

H H

2-Propanol Propanone

Oxidation

Ethanol Ethanal

–

Ethanoate

520 Chapter 12 Carbon

Ethanoic acid (also known as acetic acid) is the organic acid that we use as

vinegar when it is in the form of a weak solution (typically about 4 to 5% by

mass) in water. Some bacteria can perform the conversion of ethanol to ethanoic

acid, which can cause wines to spoil when they “turn to vinegar” due to bacterial

contamination. However, this process can also be exploited purposefully to pro-

duce the wine vinegars that are widely used in cooking. Industrially, ethanoic acid

is used in the manufacture of plastics, pharmaceuticals, dyes, and insecticides.

The carboxyl functional group is weakly acidic due to the dissociation of a

hydrogen ion from the oxygen. The result is the formation of a

carboxylate anion

and a hydrogen ion (i.e., a proton). Although it would appear that any hydrogen

on an oxygen could dissociate in a similar manner, the carboxylic acids have

a special feature that alcohols do not have (hence the latter are not acidic). Let’s

explore this property further.

Why does the carboxyl functional group dissociate?

When we draw Lewis dot structures of compounds, we must always consider

the possibility that the electrons could be placed in different locations (see Chap-

ter 8). This would generate a resonance structure of the compound. The car-

boxylate anion possesses this ability. In fact, we can draw two good resonance

structures for this ion. The resonance spreads the large negative charge across the

functional group and helps to stabilize the carboxylate by lowering the energy of

the anion.

Why doesn’t the alcohol functional group also dissociate? If a hydrogen ion

were to leave the molecule, a negative charge would reside on the oxygen. Unfor-

tunately, there aren’t any other resonance structures that we can draw for this

alkoxy anion. Therefore, the electrons cannot be spread to other atoms by reso-

nance, and the resulting alkoxyl anion is not energetically stabilized.

12.11 From Alcohols and

Carboxylic Acids to Esters

An extremely important reaction, widespread throughout both natural and in-

dustrial chemistry, takes place between the alcohol and carboxylic acid functional

groups. These two groups can react, often with an acid catalyst such as sulfuric

acid, to eliminate a molecule of water in a reaction known as a

condensation reac-

tion

. In the reaction, the carbonyl carbon from the carboxyl group becomes

bonded to the oxygen atom from the alcohol group in what is known as an ester

linkage or ester bond. Compounds containing this arrangement of atoms

(carbonyl–oxygen–carbon) are known as

esters. The simplest possible ester is

methyl methanoate (also known as methyl formate), formed when methanol

reacts with methanoic acid. Note that the ﬁrst part of the name of an ester is

derived from the alcohol that can be used in its formation, and the second part of

the name is derived from the carboxylic acid component.

 HOHHC

Methanol

OHH

Methanoic acid Methyl methanoate



HC



OHC

Ethanoic acid Ethanoate

Ethoxide

–

Compounds that contain the ester functional group often have a very fruity

aroma and in nature are found in plant oils. For example, isopentyl ethanoate has

the odor of ripe bananas, and methyl salicylate smells like wintergreen. For this

reason, esters are often used in industry to lend ﬂavors and odors to products that

we buy. Esters are also used in industry as solvents, due to their ability to dissolve

both polar and nonpolar solutes. For example, ethyl ethanoate (commonly

known as ethyl acetate) is found in cleaners and glues.

EXERCISE 12.6 Nomenclature of Esters

Provide names for each of these esters.

C Od. H

C Cc. H

b. H

Ha. H

12.11 From Alcohols and Carboxylic Acids to Esters 521

Isopentyl ethanoate Methyl salicylate

CCCH

CHO

CHCO

CH CH

CHC

First Thoughts

All ester names are in the form “ yl anoate.” The ﬁrst part of the name is

derived from the part of the molecule that was originally an alcohol, and the second

part of the name is derived from the part of the molecule that was originally a car-

boxylic acid. Therefore you need to ﬁnd the alcohol component, which is the alkyl

group linked to the O atom, count its carbon atoms to get the ﬁrst part of the name,

and then count the carbon atoms in the rest of the molecule to get the second part

of the name.

Solution

The names are (a) methyl propanoate, (b) propyl butanoate, (c) ethyl hexanoate,

and (d) butyl butanoate.

Further Insights

Working in reverse, you can ﬁgure out the name of an ester that will form between

any alcohol and any carboxylic acid, just by linking their names in the correct order

and manner. Trace through that process for the esters considered above.

PRACTICE 12.6

Shown below is the structure of benzoic acid. Can you draw the structure of ethyl

benzoate? ...ofbenzyl ethanoate?

See Problems 81–84.

12.12 Condensation Polymers

Industrial preparation of polyethylene, polyvinylchloride, and polystyrene occurs

by addition polymerization. But that is not the only way to make a polymer. A

major class of polymers that are very useful in our lives are constructed by a

condensation reaction. Condensation reactions entail the removal of a small

molecule as two larger molecules are connected. If a polymer is the product of the

reaction, we call the process

condensation polymerization.

Esters can be made by condensation reactions. The process,

esteriﬁcation, can

be used to link a variety of monomers into long polymer chains. The products of

the reaction are

polyesters, which may be familiar to you as parts of clothes,

bedding, fabrics, upholstery, ropes, belts, and so on. They are called polyesters

because of the many ester linkages that hold the monomer units within the

structure of the polymer. One of the most common polyesters is polyethylene

terephthalate (PETE), which as used for such things as soft drink and mouthwash

bottles.

522 Chapter 12 Carbon

HC CH O

CCH

Ethylene Terephthalate

Another functional group that is a part in many important condensation

polymerization reactions is the

amino functional group, —NH

. Many amines,

unfortunately, have a particularly foul odor. For instance, the common names of

some of the amines indicate the types of environments from which they were ﬁrst

isolated; putrescine (1,4-butanediamine) and cadaverine (1,5-pentanediamine)

are examples. When an amine group participates in a condensation reaction with

a carboxylic acid group, an

amide bond is formed.

The amide bond holds together the monomer units of polymers known as the

polyamides. The fabrics we know as nylons, for example, are polyamides. Nylons

are named with numbers to help indicate the structure of the polymer. For ex-

ample, Nylon [6,6] is made of monomers that each contain six carbon atoms.

Nylon [6,6] can be made when an acid chloride functional group (COCl) on one

molecule reacts with an amine functional group on another molecule. This reac-

tion is accompanied by the release of HCl. Carbon chains of different lengths can

be found within other nylon polymers.

Amide bond

Methanoic acid

(formic acid)

Methanamine

H H

C OHH++H

N-Methylmethanamide

(N-methylformamide)

12.12 Condensation Polymers 523

C CH

Amide bond

Nylon 6-6

C+H

HCl

Visualization: Synthesis of Nylon

Video Lesson: CIA

Demonstration: The Synthesis of

Nylon

12.13 Polyethers

Another important category of polymers contains the ether functional group at

regular intervals along the polymer chain. The ether group is —C—O—C—, an

oxygen atom linking two carbon atoms. Three simple examples of ethers are ethyl

methyl ether, diethyl ether, and methyl t-butyl ether (MTBE). Diethyl

ether is the “ether” that, like the chloroform mentioned earlier, was used

as an anesthetic in the early days of medicine. It is often still used in biol-

ogy classes to anesthetize and determine the characteristics of Drosophila

ﬂies. MTBE is the ether used as a fuel additive. Its octane rating is 116,

and for this reason it can help boost the rating on otherwise poor-quality

gasoline.

The properties of ethers make them ideal as solvents. Because they lack the

ability to form hydrogen bonds with themselves, they have boiling points similar

to those of the alkanes. However, the presence of an oxygen atom within the

structure indicates that they can participate in hydrogen bonding as acceptors

with other molecules that can donate a hydrogen atom. This means that they

make good solvents for chemical reactions.

Polyethers, which incorporate repeating ether linkages within very long

chain-like molecules, are widely used in adhesive resins. An example of a poly-

ether containing the ether functional group is found in the

epoxy resins. These

rather viscous polymers, used mostly as construction and household adhesives,

contain an ether linkage formed between one carbon atom that is part of a phenyl

ring, and another that is part of a methylene (CH

) group. The monomers that

make up an epoxy resin contain the phenol functional group and a triangular

ether structure known as an

epoxide.

C OCH

CHCH

Diethyl ether

Ethyl methyl ether

524 Chapter 12 Carbon

A phenol

An epoxide

Diamine solution

Acid chloride solution

The nylon rope trick. Nylon can be made

at the interface of two solutions con-

taining an acid chloride and a diamine.

The ﬁlm that forms can be pulled out

of the mixture slowly to make a long

strand of nylon polymer.

CHO OH

HO CH

Methyl t-butyl ether

(MTBE)

12.14 Handedness in Molecules 525

HERE’S WHAT WE KNOW SO FAR

■

The major components of crude oil include hydrocarbons.

■

Crude oil has many uses, including serving as fuel and supplying feedstock

molecules for industrial processes.

■

Manipulation of the hydrocarbons can yield a variety of molecules containing

different functional groups.

■

Functional groups are common speciﬁc arrangements of atoms within a mol-

ecule that impart similar physical and chemical properties to the molecule.

■

Organic molecules are named by applying a set of rules established by the

International Union of Pure and Applied Chemistry (IUPAC).

12.14 Handedness in Molecules

Symmetry abounds in nature. Take, for instance, the symmetry of a person. The

left-hand side of your friend appears to be a mirror image of the right-hand side.

Proof of this can be found in your own hands. Hold your hand to a mirror such

as that shown in Figure 12.15. What do you see? Your other hand is the

mirror image. What’s more interesting is that your left and right hands

(despite being mirror images) are not superimposable. That is to say,

your left hand and your right hand cannot be lined up perfectly. Try

placing a left-handed glove on your right hand. It just doesn’t ﬁt.

Molecules can also exhibit this handedness. In chemistry, we say

that “handed” molecules are

chiral, a term derived from the Greek cheir

(“hand”). A chiral object has a nonsuperimposable mirror image.

Those molecules that lack

chirality are said to be achiral, and they have

a superimposable mirror image. Every chiral molecule possesses a twin

that has the same chemical formula, the same structure, but a different

arrangement of atoms in three-dimensional space.

What makes a molecule chiral? Carbon-based molecules are chiral

when they contain a carbon atom that is attached to four different groups.

These

chiral centers exist in many molecules in nature. Let’s examine

a derivative of methane to explain this feature. Bromochloroﬂuo-

romethane (CHBrClF) contains a carbon atom attached to four differ-

ent groups. A mirror image of this molecule (see Figure 12.16) shows

this molecule to have handedness. These two molecules are

stereoisomers. They

are a special kind of structural isomers that differ in their 3-D arrangements of

atoms, rather than in the order in which the atoms are bonded.

The right-handed molecule and the left-handed molecule have almost identi-

cal physical properties because they have the same chemical structure. They are

different, however. For instance, the receptors in your nose perceive different aro-

mas based on their interaction with molecules. Carvone, shown in Figure 12.17,

a molecule your nose might encounter in the kitchen, possesses a chiral carbon

and therefore exists as two stereoisomers. One of the isomers smells like caraway

seeds; the other smells like spearmint.

Chiral molecules also exhibit the ability to rotate the plane of polarized light.

Light, passed through a polarizing ﬁlter (such as the one in most sunglasses), is

composed of electromagnetic waves that are aligned in one direction (such as the

up-and-down direction). This polarized light interacts with the two stereoiso-

mers of a chiral molecule to the same degree, but one of the isomers rotates the

light to the left and the other to the right, as shown in Figure 12.18.

FIGURE 12.15

Chiral objects have a nonsuperimposable mirror

image. The mirror image of an achiral object is

superimposable.

Br Br

Cl Cl

FIGURE 12.16

Some organic molecules are also chiral.

The image and the original are non-

superimposable.

526 Chapter 12 Carbon

CHC

Caraway seed oil Spearmint oil

FIGURE 12.17

The isomers of carvone.

Unpolarized

light

Polarized

light

Polarizer

Light

source

Polarizer

prism

Prism

axis

Unpolarized

light

Polarized

light

Rotated

polarized

light

Degree of

rotation

Analyzer

prism

Sample tube

(containing

an optically

active compound)

FIGURE 12.18

Plane polarized light is rotated as it interacts

with chiral molecules.

EXERCISE 12.7 Chiral Drugs

Thalidomide was used as a drug that relieved morning sickness in pregnant women

in the 1950s and 1960s. Although the FDA was hesitant (because of some neurolog-

ical side effects) to approve the drug for use in the United States, thalidomide found

widespread use in Europe and Canada. On the basis of the structure given here,

identify the chiral center in the molecule.

First Thoughts

We’ll examine the molecule, looking for carbons that are bonded to four different

groups. A helpful starting point is to ignore all carbons that contain double bonds

or more than one hydrogen atom.

Solution

Further Insight

The existence of a chiral center in thalidomide implies that there are two molecules

with the same structure and physical properties. It also implies that each of the two

stereoisomers might have different interactions with receptors in the body. In fact,

this is the case. Whereas one of the stereoisomers does exert a powerful sedative ef-

fect and reduce nausea, the other isomer is a powerful teratogen. Teratogens cause

terrible birth defects.Women who used the drug during pregnancy gave birth to ba-

bies with a wide variety of defects, such as deformed or missing limbs. Thalidomide

isn’t used to treat morning sickness anymore, though it is used to treat some people

with leprosy.

PRACTICE 12.7

Identify the chiral centers in each of the molecules below.

See Problems 95 and 96.

12.15 Organic Chemistry and

Modern Drug Discovery

Perhaps one of the most profound impacts of organic chemistry on modern

society has been its key role in pharmaceutical science. Historically, chemists and

medical researchers have analyzed natural product extracts for effectiveness

in curing diseases. Many times these plant extracts are the same ones identiﬁed in

folk medicine as curatives for common maladies. Ultimately, there must be some

component or collection of compounds present in the extract mixture that is

responsible for their effectiveness. Organic chemists can purify the active con-

stituents of complex mixtures originating from such natural sources, and very

often, this active constituent turns out to be a single compound. These com-

pounds are nearly always based on a carbon framework. Organic chemists can

determine the structure of these compounds and can even synthesize them using

simple starting materials. They can also make clever improvements on these nat-

ural products by rationally changing structural features (and, therefore, speciﬁc

properties) of the molecule.

HCC

12.15 Organic Chemistry and Modern Drug Discovery 527