The Foundations of Chemistry

Crystals of glycine viewed under

polarized light. Glycine, the simplest

amino acid, has the structure shown

in the text, with RH.

27-14 Some Derivatives of Carboxylic Acids 1079

where R can be either an alkyl or an aryl group. -Amino acids are the components of

proteins, which make up the muscle and tissue of animals. Many other acids are impor-
tant in the metabolism and synthesis of fats by enzyme systems. Acetic acid (the acid in
vinegar) is the end product in the fermentation of most agricultural products. It is the
fundamental unit used by living organisms in the biosynthesis of such widely diverse classes
of natural products as long-chain fatty acids, natural rubber, and steroid hormones.

SOME DERIVATIVES OF CARBOXYLIC ACIDS

Three important classes of acid derivatives are formed by the replacement of the hydroxyl

group by another atom or group of atoms. Each of these derivatives contains an acyl group.

Aromatic compounds of these types (with Raryl groups) are also encountered

frequently.

Acyl Halides (Acid Halides)

The acyl halides,sometimes called acid halides,are structurally related to carboxylic

acids by the replacement of the XOH group by a halogen, most often XCl. They are
usually named by combining the stems of the common names of the carboxylic acids with
the suffix -yland then adding the name of the halide ion. Examples are

Acid halides are very reactive and have not been observed in nature.

Esters

Esters can be thought of as the result of removing one molecule of water from a carboxylic
acid and an alcohol. Removing a molecule of water from acetic acid and ethyl alcohol
gives ethyl acetate.

CH 3 C

O

OH HO CH 3 C

O

CH 2 CH 3 OCH 2 CH 3 H 2 O

acetic acid ethyl alcohol ethyl acetate

 

C Cl

O

C Cl

O

CH 3 CH 3 CH 2 CH 2 C F

O

acetyl chloride butyryl fluoride benzoyl chloride

O

R C Cl

an acyl chloride

(an acid chloride)

O

R C NH 2

an amide

O

R C O R

an ester

27-14

C OH

H O

NH 2

R C

As we will see in Section 28-6, one

method of forming esters involves

acid-catalyzed reaction of an alcohol

with a carboxylic acid.