A secondary amine has the general structure R₂-NH, where two organic groups (R) are attached to the nitrogen atom. These groups can be alkyl or aryl substituents. The formation of secondary amines involves the replacement of two hydrogen atoms in ammonia (NH₃) by organic groups. This process occurs through nucleophilic substitution reactions, where ammonia reacts with alkyl or aryl halides, resulting in the substitution of hydrogen atoms with the organic groups. The resulting secondary amine exhibits a trigonal pyramidal geometry around the nitrogen atom, with the two organic groups and one hydrogen arranged in a trigonal planar fashion.