(4) You will notice in the compounds above that they are not pure aromatic
hydrocarbons because they contain elements other than carbon and hydrogen. These
additional elements are the basis for the classification of substituted organic compounds
and are called functional groups. The important functional groups will be considered in
the following paragraphs.
3-7.
INTRODUCTION TO FUNCTIONAL GROUPS
There are millions of organic compounds known to exist, and most are more
complex than the simple hydrocarbons we have discussed. To facilitate the study of
their reactions and properties, they are conveniently classed according to the functional
groups they contain. A functional group is a group of atoms or a single atom that is
substituted for a hydrogen or a hydrocarbon. These groups generally determine the
types of reactions and properties of these more complex compounds. (A summary of
the properties and reactions of the compounds contained in paragraphs 3-8 through
3-16 is tabulated in Table 3-3, pages 3-14 and 3-15.)
3-8.
ALCOHOLS
Alcohols are hydroxyl (-OH) derivatives of hydrocarbons formed by replacing a
hydrogen with the hydroxyl radical and are of the general form R-OH where R
represents the hydrocarbon. There are three classes of alcohols: primary, secondary,
and tertiary. A primary alcohol is one in which the hydroxyl group is attached to a
carbon atom which, in turn, is attached to not more than one other carbon atom. A
secondary alcohol is one in which the hydroxyl group is attached to a carbon atom
which in turn, is connected to two carbon atoms. A tertiary alcohol is one in which the
hydroxyl group is attached to a carbon atom which in turn, is attached to three other
carbon atoms.
CH3-CH2-OH
CH3-CH-CH3
CH3
Primary Alcohol
OH
CH3--C--CH3
Ethanol
(ethyl alcohol)
Secondary Alcohol
OH
2-propanol
(isopropyl alcohol)
Tertiary Alcohol
Alcohols that contain two or more hydroxyl groups are referred to as polyhydroxy
alcohols. An example you will encounter frequently in this course and on the job is
glycerin, which is:
CH2--CH--CH2
OH
OH OH
3-8
MD0803