111 Functional groups in reactions
Functional groups^1 in reactions make your life easier as an organic chemist because they
draw your attention right to where the action is. Any time a reaction is going to occur, you
can be almost certain that it is going to take place at a functional group.
There are many functional groups of interest to organic chemists. Here are a few:
- Halides
These groups are all made up of a single atom in Group 17 of the Periodic Table, which
is known as the halogen group, bonded to a carbon atom. They include fluorine, chlorine,
bromine, and iodine. Astatine is also a halogen, but it is rarely discussed because it is
not readily found in nature and is radioactive. Their electronegativities vary from fluorine
with 4.0 to iodine with 2.5, which is approximately the same value that carbon has. Each
of these atoms are able to form a single bond with a carbon atom, replacing hydrogen in
alkanes and adding across multiple bonds in alkenes and alkyne. Of the four, fluorine is the
most reactive and iodine is the least. Because of their intermediate reactivity, chlorine and
bromine are often more useful in many reactions.
- Carbonyl
This group consists of an oxygen atom doubly bonded to a carbon atom. Carbonyl groups
are important because the oxygen atom, with an electronegativity of 3.5, shifts electron
density away from the rest of the molecule and towards itself. Carbonyls are a key ingredient
in aldehydes, ketones, carboxylic acids, esters, and amides.
- Hydroxyl
This group consists of a hydrogen atom singly bonded to an oxygen atom. The electroneg-
ativity difference between hydrogen, which has an electronegatity of 2.1, and oxygen, 3.5,
pulls electrons away from the hydrogen and makes it somewhat acidic. This acidic character
varies depending on the composition of the rest of the molecule. Hydroxyl groups are found
in alcohols, phenols, enols, and carboxylic acids.
1 https://en.wikibooks.org/wiki/Organic_Chemistry%2FIntroduction_to_functional_groups