An atom or group of atoms or presence of double or triple bond which determines the characteristic properties of an organic compound is known as the functional group. The remaining part of the molecule mainly determines the physical properties such as melting point, boiling point, density, etc. For example, - OH group is the functional group of alcohols, which gives characteristics properties of alcohols. The characteristic properties of carboxylic acids are due to the presence of - COOH group in them. Therefore, functional group of carboxylic acids is - COOH group.
11.5.1 Functional Groups Containing Carbon, Hydrogen and Oxygen
The organic compounds containing carbon, hydrogen and oxygen as functional groups are alcohols, ethers, aldehydes, ketones, carboxylic acids and esters. Their class name, functional group, class formula and examples are given in the Table 11.4.
(i) Alcoholic Group
The functional group of alcohol is - OH. Their general formula is ROH. Where R is any alkyl group.
CH3- OH Methyl alcohol
CH3- CH2- OH Ethyl alcohol
CH3- CH2- CH2- OH n- Propyl alcohol
(ii) Ether Linkage
The functional group of ether is C- O- C. Their general formula is R- O- R' where R and R' are alkyl groups.
R and R' may be same or different, such as:
H3C- O- CH3 Dimethyl ether, C2H5- O- C2H5, Diethyl ether H3C- O- C2H5, Ethyl methyl ether
(iii) Aldehyde Group
Aldehyde family consists of functional group.
Their general formula is RCHO.