Answer. Hydrocarbons are regarded as the parent organic compounds because other organic compounds are considered to be derived from then by replacement of one or more hydrogen atoms by other atoms or group of atoms. For example, by replacing hydrogen atom with hydroxyl group alcohol is produced.
CH3-H CH3-OH
CH3-CH2-H CH3CH2-OH
By replacing hydrogen atom with -NH2 (amino) group amine is formed.
CH3-CH2-NH2