Amines and their Derivatives | Organic Chemistry 3
Nomenclature of Amines
Amines:
Derivatives of ammonia NH3, in which one, two or three of the H have been replaced by alkyl or aryl groups
Nomenclature:
The -ane ending of the corresponding alkane is replace by -anamine. The rules for naming alcohols also apply to amines
For secondary and tertiary amines:
- largest alkyl group = main chain
- other alkyl groups = substituents named as prefixes preceded by N-
The amine functional group has the lowest order of priority of all functional groups (except alkene and alkyne). The prefixe amino- is used when the amine is a substituent
Properties of Amines
Properties:
Amines have properties similar to alcohols and ethers. They can:
- serve as nucleophile
- participate in hydrogen bonding (high boiling point + soluble in water)
- be both basic and acidic:
Alkanamine is tetrahedral
Comparison with alcohols:
Oxygen is more electronegative than nitrogen
⇒ amines are less acidic than alcohols
⇒ amines are more basic and nucleophilic than alcohols and ethers
⇒ amines have weaker hydrogen bonding than alcohols
Absorption spectroscopy:
NMR: 1H broad signal and variable δ (1.0-2.5 ppm)
IR: N-H stretching ⇒ broad band ~ 3250-3500 cm-1
Preparation of Amines
Amines by alkylation:
Mechanism:
- Nucleophilic substitution:
- Deprotonation:
- Subsequent alkylations
Amines from azides:
Amines by reductive amination:
Mechanism:
- Condensation:
- Reduction:
Amines from carboxylic amides:
Amines from nitriles:
Hofmann Elimination
Mechanism:
Mannich Reaction
Mechanism:
The Mannich reaction can be thought of as a variation of the aldol condensation
- Iminium ion formation:
- Carbon-carbon bond formation:
- Deprotonation: