Question

(a) What is meant by a functional group? Explain with an example.
(b) Write three common functional groups present in organic compounds. Giver their symbols/formulae.
(c) Name the functional groups present in the following compounds:
(i) CH₃COOH
(ii) CH₃CH₂CHO
(iii) C₂H₅OH
(iv) CH₃COCH₂CH₃
(d) Name the functional group which always occurs in the middle of a carbon chain.
(e) Draw the structures for the following compounds:
(i) Ethanal
(ii) Propanal
(iii) Butanal
(iv) Pentanal

Answer 1

(a) Functional group: An atom or a group of atoms which determine the properties of an organic compound is called a functional group.
For example: The alcohol group -OH is also known as an alcoholic group or hydroxyl group. The compounds in which the alcohol group is present are termed as alcohols. The general formula of an alcohol is R-OH (R is an alkyl group) like ethanol which has the molecular formula C₂H₅OH. All the compounds having this functional group will have similar properties.

(b) The three common functional groups present in the organic compounds are as follows:

Functional groups	Aldehyde group	Halo group	Ketone group
Symbol	-CHO	(-X)	-CO-
Formula	R-CHO	R-X	R-CO-R'

(c) (i) The functional group present in CH₃COOH is carboxylic acid group (-COOH).
(ii) The functional group present in CH₃CH₂CHO is the aldehyde group (-CHO).
(iii) The functional group present in C₂H₅OH is the alcohol group (OH).
(iv) The functional group present in CH₃COCH₂CH₃ is the ketone group (-CO-).

(d) The functional group which always occurs in the middle of the carbon chain is the ketone group (-CO-). In a ketone, a carbon atom is bonded to one oxygen through a double bond. The two remaining free electrons in the carbon atom are shared with two different alkyl groups. This is why the -CO- group always occurs in the middle of the carbon chain.

(e) Molecular structures of the compounds are as follows:
(i)

(ii)

(iii)

(iv)