## 20.1 Amines Amines are a group of organic compounds containing a nitrogen atom with a lone pair of electrons, bonded to alkyl or aryl groups. They are considered derivatives of ammonia ($NH_3$) where one or more hydrogen atoms have been replaced by these groups. --- ## Classification of Amines Amines are classified based on the number of carbon atoms (from alkyl or aryl groups) directly attached to the nitrogen atom. They are categorized into three main types: * (a) Primary (1°) amines * (b) Secondary (2°) amines * (c) Tertiary (3°) amines --- ### (a) Primary (1°) Amines In primary amines, only one alkyl or aryl group is directly bonded to the nitrogen atom. They have the general formula: $$R-NH_2$$ **Examples of Primary Amines:** * Methylamine: $CH_3-NH_2$ * Ethylamine: $CH_3CH_2-NH_2$ * Propylamine: $CH_3CH_2CH_2-NH_2$ * Aniline (an aryl amine): $C_6H_5-NH_2$ --- ### (b) Secondary (2°) Amines In secondary amines, two alkyl or aryl groups are directly bonded to the nitrogen atom. They have the general formula: $$R-NH-R'$$ (where R and R' can be the same or different) **Examples of Secondary Amines:** * Dimethylamine: $CH_3-NH-CH_3$ * Ethylmethylamine: $CH_3CH_2-NH-CH_3$ * Diethylamine: $CH_3CH_2-NH-CH_2CH_3$ --- ### (c) Tertiary (3°) Amines In tertiary amines, three alkyl or aryl groups are directly bonded to the nitrogen atom. They have the general formula: $$R_3N$$ (where the R groups can be the same or different) **Example of a Tertiary Amine:** * Trimethylamine: $(CH_3)_3N$ --- ## Basicity and Physical Properties The presence of a lone pair on the nitrogen atom makes amines basic and nucleophilic. In the gas phase, the basicity increases with the number of electron-donating alkyl groups. For more information on the electronic structure of nitrogen, see and . ---