What is the structural formula of a primary amine?

The correct choice describes a primary amine as having the structural formula R-NH2, where R represents an alkyl group. This is significant because in a primary amine, the nitrogen atom is bonded to one alkyl or aryl group and has two hydrogen atoms attached.

This structure differentiates primary amines from secondary and tertiary amines. In secondary amines, nitrogen is bonded to two carbon-containing groups, while in tertiary amines, it is bonded to three such groups. The presence of two hydrogen atoms in primary amines allows for unique reactivity and solubility properties, which are essential in organic chemistry.

Choosing this option aligns with the fundamental definitions and structural characteristics of amines. The designation of an amine specifically requires the identification of how many carbon chains or groups are attached to the nitrogen, directly affecting its classification as primary, secondary, or tertiary.