Worked Example 15.1 Drawing and Classifying Amines from Their Names

1. Worked Example 15.1 Drawing and Classifying Amines from Their Names Write the structure of N,N-diethylbutylamine and identify it as a primary, secondary, or tertiary amine. Analysis Look for terms within the name that provide clues about the parent compound and its substituents. For example, the word “butyl” immediately preceding the -amine suffix indicates that butylamine, the 4-carbon alkyl amine, is the parent compound. The N,N indicates that two other groups are bonded to the amino nitrogen, and the diethyl indicates they are both ethyl groups. Solution The structure shows that three alkyl groups are bonded to the N atom, so this must be a tertiary amine.

2. Worked Example 15.2 Naming and Classifying an Amine from Its Structure Name the following compound. Is it a primary, secondary, or tertiary amine? Analysis Determine how many organic groups are attached to the nitrogen. We can see that two carbon groups are bonded to the nitrogen. Since the cyclohexyl group is the largest alkyl group bonded to N, the compound is named as a cyclohexylamine. One methyl group is bonded to the nitrogen; we indicate this with the prefix N. Solution The name is N-methylcyclohexylamine. Because the compound has two groups bonded to N, it is a secondary amine.

3. Worked Example 15.3 Classifying a Cyclic Amine from Its Structure The following heterocyclic amine is named octahydroindolizine. Is it a primary, secondary, or tertiary amine? Analysis Start by looking at the nitrogen; we can see that it is attached to three different carbons (as indicated by red, blue, and black bond lines). Even when the nitrogen is part of a ring, an amine will be classified by the number of organic groups that are bonded to it. Solution In this molecule, three individual carbon groups are bound to N; it therefore is a tertiary amine.

4. Worked Example 15.4 Amines as Bases in Water Write balanced equations for the reaction of ammonia with water and for the reaction of ethylamine with water. Label each species in your equations as either an acid or a base. Analysis Determine which species is the base and which is the acid. Remember that the base will accept a hydrogen ion from the acid. Review the definitions for a Brønsted–Lowry base (Section 10.3) and a Lewis base (Section 15.2). Solution Like ammonia, amines have a lone pair of electrons on the nitrogen atom. Because ammonia is a base that reacts with water to accept a hydrogen ion (which bonds to the lone pair), it is reasonable to expect that amines are bases that react in a similar manner. Notice that in both cases water acts as an acid because it donates a hydrogen ion to the nitrogen.