25.3. Functional Groups http://www.ck12.org
- Identify and name the alkyl group (R’) that has replaced the hydrogen of the hydroxyl group. This is the first
part of the ester name. - Name the carboxylic acid portion of the molecule (R-COO), but change the ending of the name from –oic acid
to –oate. This is the second part of the ester name. - Leave a space between the alkyl group name and the name of the carboxylic acid derivative.
In cases where the R’ group is relatively small, esters have lower boiling points than the carboxylic acids from
which they were derived. This is due to the fact that esters cannot form hydrogen bonds with each other, since they
no longer possess the O-H bond that is present in the acid form. Esters with very short carbon chains are somewhat
soluble in water, while those with longer chains are less soluble.
Esters are very commonly found in plants and are responsible for many distinctive odors and flavors. For example,
methyl salicylate has the odor and flavor of oil of wintergreen, while propyl ethanoate smells and tastes like a pear (
Figure25.20).
FIGURE 25.20
Esters are responsible for many aro-
mas and flavors in natural products.
Methyl salicylate (IUPAC: methyl 2-
hydroxybenzoate) is found in the plant
that provides oil of wintergreen, which
is used in mints and candies. Propyl
ethanoate is an ester found in pears.At one time, these compounds had to be isolated from their natural sources in order to be used as food additives, but
chemists are now able to synthesize these and many other naturally occurring compounds in the laboratory.
Amines
Anamineis an organic compound in which one or more of the hydrogen atoms of ammonia (NH 3 ) is replaced by an
alkyl group(Figure25.21). The general structure of an amine can be abbreviated as R−NH 2 , where R is a carbon