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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

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Solution

(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)

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