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Functional Groups

This is one more basic exercise. A functional group may be described as:

  • The part of the molecule which is responsible for its characteristic reactions.
  • The group that functions in a reaction
  • Thus a double bond is the functional group of an alkene because that is the place addition, which is its characteristic reaction takes place.
  • Similarly a triple bond is the functional group of an alkyne
  • There are many functional groups, some of which are listed below.
  • In the following exercise the general formula and the expanded structure of the general formula of some functional groups is shown. Also the molecular formula for some specific molecule is shown. write its expanded structure


An alcohol has an -OH group bonded to a sp3 carbon.

Alcohol Functional Group Example


It has an -OH group directly attached to a carbon of the aromatic ring (benzene).

Phenol Functional Group Example


The group –CHO, represents an aldehyde. This does not mean the H is bonded to C and O, the correct structure is shown on the right.

Aldehyde Functional group Example