Which of the following compounds is a secondary amine?

• A. ${\mathrm{CH}}_3\mathrm{COOH}$ (acetic acid)
• B. ${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{NH}$₂ (ethylamine)
• C. ${\mathrm{CH}}_3{\mathrm{CH}}_3{\mathrm{CH}}_{3}N$ (trimethylamine)
• D. ${\mathrm{CH}}_3{\mathrm{CH}}_3\mathrm{NH}$ (dimethylamine)

Answer: (D)

Verified step by step guidance

1. Understand the definition of amines based on the number of alkyl or aryl groups attached to the nitrogen atom: a primary amine has one alkyl/aryl group, a secondary amine has two, and a tertiary amine has three.
2. Analyze each compound's structure to count how many carbon-containing groups are bonded directly to the nitrogen atom.
3. For acetic acid (CH\_3COOH), recognize that it is a carboxylic acid, not an amine, so it cannot be classified as primary, secondary, or tertiary amine.
4. For ethylamine (CH\_3CH\_2NH\_2), note that the nitrogen is bonded to only one alkyl group (ethyl), making it a primary amine.
5. For trimethylamine (CH\_3CH\_3CH\_3N), observe that the nitrogen is bonded to three methyl groups, classifying it as a tertiary amine; therefore, the compound with two alkyl groups attached to nitrogen (dimethylamine) is the secondary amine.