Concept:A tertiary amine has the nitrogen atom bonded to three carbon-containing groups.
Explanation:Count the number of alkyl or aryl groups attached to nitrogen in each compound.
Cyclohexanamine has one alkyl group, so it is a primary amine.
Ethane-1,2-diamine contains two primary amine groups, so it is not tertiary.
N-Phenylbenzeneamine has two aryl groups on nitrogen, making it a secondary amine.
N-Ethyl-N-Methylpropan-2-amine has ethyl, methyl, and propan-2-yl groups attached to the same nitrogen atom.
Since three carbon substituents are attached to nitrogen, it is a tertiary amine.
Answer:D.
N-Ethyl-N-Methylpropan-2-amine
