SUMMARY OF FUNCTIONAL GROUPS
Some important functional groups and the corresponding classes of related compounds
are summarized in Figure 27-20.
FUNDAMENTAL CLASSES OF ORGANIC REACTIONS
Organic compounds display very different abilities to react, ranging from the limited reac-
tivity of hydrocarbons and fluorocarbons to the great variety of reactions undergone by
the millions of organic molecules that contain several functional groups. Reactivity
depends on structure. We can usually predict the kinds of reactions a compound can
undergo by identifying the functional groups it contains. But the electronic and structural
features that are neara functional group can also affect its reactivity. One of the fascina-
tions of organic chemistry is our ability to “fine-tune” both physical and chemical
properties by making small changes in structure. The successes of this approach are innu-
merable, including the development of fuels and their additives or alternatives, the
improvement of pharmaceuticals to enhance their effectiveness and minimize their ill
effects, and the development of polymers and plastics with an incredible variety of prop-
erties and uses.
In the following sections of this chapter we will present a few of the kinds of reactions
that organic compounds undergo. A topic of such vast scope as reactivity of organic
compounds can be made manageable only if we divide our study of this field into subtopics.
Nearly all organic transformations involve at least one of three fundamental classes of
reactions. The following three sections will address substitution, addition, and elimina-
tion reactions. We will also look at some reaction sequences that combine reaction steps
from more than one of the fundamental classes.
SUBSTITUTION REACTIONS
In a substitution reactionan atom or a group of atoms attached to a carbon atom
is removed, and another atom or group of atoms takes its place. No change occurs
in the degree of saturation at the reactive carbon atom.The saturated hydrocarbons (alkanes and cycloalkanes) are chemically rather inert
materials. For many years they were known as paraffinsbecause they undergo few reac-
tions. They do not react with such powerful oxidizing agents as potassium permanganate
and potassium dichromate. They do react with the halogens, however, with oxygen when
ignited, and with concentrated nitric acid. As expected, members of a homologous series
(see Section 27-1) have similar chemical properties. If we study the chemistry of one of
these compounds, we can make predictions about the others with a fair degree of certainty.
The saturated hydrocarbons can react without a big disruption of the molecular struc-
ture only by displacement, orsubstitution of one atom for another.At room temperature,
chlorine and bromine react very slowly with saturated straight-chain hydrocarbons. At
27-16
27-15
27-16 Substitution Reactions 1085