129 Overview of Functional Groups
129.1 Introduction
The number of known organic compounds is quite large. In fact, there are many times more
organic compounds known than all the other (inorganic) compounds discovered so far, about
7 million organic compounds in total. Fortunately, organic chemicals consist of a relatively
few similar parts, combined in different ways, that allow us to predict how a compound we
have never seen before may react, by comparing how other molecules containing the same
types of parts are known to react.
These parts of organic molecules are calledfunctional groups. The identification of
functional groups and the ability to predict reactivity based on functional group properties
is one of the cornerstones of organic chemistry.
Functional groups are specific atoms, ions, or groups of atomshaving consistent
properties. A functional group makes up part of a larger molecule.
For example,-OH, the hydroxyl group that characterizes alcohols, is an oxygen with a
hydrogen attached. It could be found on any number of different molecules.
Just as elements have distinctive properties, functional groups have characteristic
chemistries. An-OHgroup on one molecule will tend to react similarly, although perhaps
not identically, to an-OHon another molecule.
Organic reactions usually take place at the functional group, so learning about the
reactivities of functional groups will prepare you to understand many other things about
organic chemistry.
129.2 Memorizing Functional Groups
Don’t assume that you can simply skim over the functional groups and move on. As you
proceed through the text, the writing will be in terms of functional groups. It will be
assumed that the student is familiar with most of the ones in the tables below. It’s simply
impossible to discuss chemistry without knowing the ”lingo”. It’s like trying to learn French
without first learning the meaning of some of the words.
One of the easiest ways to learn functional groups is by making flash cards. Get a pack of
index cards and write the name of the functional group on one side, and draw its chemical
representation on the other.
For now, a list of the most important ones you should know is provided here. Your initial
set of cards should include, at the very least: Alkene, Alkyne, Alkyl halide (or Haloalkane),