15.11 Amines: Structures and Names

Learning Objectives

  1. Identify the general structure for an amine.
  2. Identify the functional group for amines.
  3. Determine the structural feature that classifies amines as primary, secondary, or tertiary.
  4. Use nomenclature systems to name amines.

Amines are classified according to the number of carbon atoms bonded directly to the nitrogen atom. A primary (1°) amineA compound that has only one alkyl or aryl group on the nitrogen atom. has one alkyl (or aryl) group on the nitrogen atom, a secondary (2°) amineA compound that has two alkyl or aryl groups on the nitrogen atom. has two, and a tertiary (3°) amineA compound that has three alkyl or aryl groups on the nitrogen atom. has three (Figure 15.5 “The Structure of Amines Compared to Water, an Alcohol, and an Ether”).

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Figure 15.5 The Structure of Amines Compared to Water, an Alcohol, and an Ether.

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The common names for simple aliphatic amines consist of an alphabetic list of alkyl groups attached to the nitrogen atom, followed by the suffix –amine. (Systematic names are often used by some chemists.) The amino group -NH2 is named as a substituent in more complicated amines such as those that incorporate other functional groups or in which the alkyl groups cannot be simply named.

Example 9

Name each compound and classify as 1o, 2o, or 3o.

  1. CH3CH2CH2NH2
  2. image
  3. CH3CH2NHCH2CH3
  4. CH3CH2CH2NHCH3

Skill-Building Exercise

Name and classify each compound.

  1. image
  2. image
  3. CH3CH2CH2CH2NH2

  4. CH3CH2CH2NHCH2CH2 CH3

Example 10

Draw the structure for each compound and classify as primary, secondary, or tertiary.

  1. isopropyldimethylamine
  2. dipropylamine

Skill-Building Exercise

Draw the structure for each compound and classify.

  1. ethylisopropylamine

  2. diethylpropylamine

The primary amine in which the nitrogen atom is attached directly to a benzene ring has a special name—aniline. Aryl amines are named as derivatives of aniline.

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Example 11

Name this compound.

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Skill-Building Exercise

  1. Name this compound.

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Example 12

Draw the structure for 4-ethylaniline and classify.

Skill-Building Exercise

  1. Draw the structure for 4-isopropylaniline and classify.

Example 13

Draw the structure for 2-amino-3-methylpentane.

Skill-Building Exercise

  1. Draw the structure for 2-amino-3-ethyl-1-chloroheptane.

Ammonium (NH4+) ions, in which one or more hydrogen atoms are replaced with alkyl groups, are named in a manner analogous to that used for simple amines. The alkyl groups are named as substituents, and the parent species is regarded as the NH4+ ion. For example, CH3NH3+ is the methylammonium ion. The ion formed from aniline (C6H5NH3+) is called the anilinium ion.

Example 14

Name each ion.

  1. CH3NH3+
  2. (CH3)2NH2+
  3. (CH3)3NH+
  4. (CH3)4N+ (note that this is a quaternary or 4o amine)

Skill-Building Exercise

Name each ion.

  1. CH3CH2NH3+

  2. (CH3CH2)3NH+

  3. (CH3CH2CH2)2NH2+

  4. (CH3CH2CH2CH2)4N+

Concept Review Exercises

  1. To what inorganic compound are the amines related?

  2. How are amines classified?

Key Takeaways

  • An amine is a derivative of ammonia in which one, two, or all three hydrogen atoms are replaced by hydrocarbon groups.
  • The amine functional group is as follows:

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  • Amines are classified as primary, secondary, or tertiary by the number of hydrocarbon groups attached to the nitrogen atom.
  • Amines are named by naming the alkyl groups attached to the nitrogen atom, followed by the suffix –amine.

Exercises

  1. Draw the structure for each compound and classify the amine as primary, secondary, or tertiary.

    1. dimethylamine
    2. diethylmethylamine
    3. 2-aminoethanol
  2. Draw the structure for each compound and classify the amine as primary, secondary, or tertiary.

    1. 3-aminopentane
    2. 1,6-diaminohexane
    3. ethylphenylamine
  3. Draw the structure for each compound.

    1. aniline
    2. 3-bromoaniline
  4. Draw the structure for each compound.

    1. 2-chloroaniline
    2. 3,5-dichloroaniline
  5. Name each compound.

    1. CH3CH2CH2NH2
    2. image
    3. image
  6. Name each compound.

    1. (CH3CH2)3N
    2. (CH3CH2)2NCH3
  7. Draw the structure for each compound.

    1. dimethylammonium chloride
    2. anilinium chloride
  8. Draw the structure for each compound.

    1. ethylmethylammonium chloride
    2. anilinium nitrate
  9. Name each compound.

    1. [CH3CH2NH2CH2CH3]+Br
    2. [(CH3CH2)3NH]+I
  10. Name each compound.

    1. [(CH3)3NH]+NO3
    2. [(CH3CH2)2NH2]+Cl