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SolutionsAmines, anilines and other nitrogen functions

1. Primary, secondary, tertiary or quaternary

Classify each nitrogen compound:

  1. CH3CH2NH2
  2. (CH3CH2)2NH
  3. (CH3)3N
  4. (CH3)4N+ Cl−
  5. Piperidine
  6. C6H5NH2
  1. Primary amine: the nitrogen is bonded to a single carbon.
  2. Secondary amine.
  3. Tertiary amine.
  4. Quaternary ammonium salt: the nitrogen has four C–N bonds and a positive charge.
  5. Cyclic secondary amine.
  6. Aromatic primary amine (aniline).

Unlike alcohols, the classification refers to the number of carbons bonded to the nitrogen, not to the type of carbon bearing the amino group: tert-butylamine, (CH3)3CNH2, is a primary amine.

2. Base and nucleophile

Which structural feature explains why amines are both bases and nucleophiles? Give an example of each behaviour.

The lone pair of the nitrogen. As a base, the amine takes up a proton: CH3NH2 + H2O ⇌ CH3NH3+ + HO−. As a nucleophile, it attacks an electron-deficient carbon: CH3NH2 + CH3I → (CH3)2NH2+ I− (alkylation), or the carbonyl carbon of an aldehyde or ketone (imine formation).

3. Nitrogen families

Give the oxidation state of nitrogen in: CH3NH2, CH3N=C=O, CH3N3 (the atom bonded to carbon) and CH3NO2.

  1. CH3NH2: −3.
  2. CH3N=C=O: −3 (nitrogen is more electronegative than carbon and keeps all the electrons of its bonds to it).
  3. CH3–N=N+=N−: −1 on the nitrogen bonded to carbon (the average oxidation state of the three nitrogens is −1/3).
  4. CH3NO2: +3.

This is why nitro compounds, azides and isocyanates can be converted into amines by reduction (or, for isocyanates, by hydrolysis).

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