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Amines

Nomenclature:
Functional group suffix = -amine (review)
Functional group prefix = amino
Primary, secondary, tertiary or quaternary ? Amines are described as primary (1o), secondary (2o), tertiary (3o) or quaternary (4o) depending on how many alkyl substituents are attached to the N atom (note the difference compared with alcohols).  Quaternary amines are also known as ammonium cations.
 

ammonia
ethyl amine
dimethyl amine
trimethyl amine
tetramethyl ammonium
 
1o
 2o
3o
4o
Question
Check the designations by counting the number of C atoms attached to the N atom in each of the examples shown above.

Physical Properties:

Structure: Reactivity:
 
electrostatic potential of methyl amine The image shows the electrostatic potential for methylamine, CH3NH2. The more red an area is, the higher the electron density and the more blue an area is, the lower the electron density. 
  • The amine N atom is a region of high electron density (red) due to the lone pair.
  • Amine N atoms are Lewis bases, (alkyl ammonium pKa ~ 10, aryl ammonium pKa ~ 5)
  • Amines can react as either bases or nucleophiles at the nitrogen.
  • There is low electron density (blue) on H atom of the -NH group.
  • Removal of the proton generates the amide ion

  • (care : not to be confused with the carboxylic acid derivative RCONH2
  • The -NH group is a very poor leaving group and needs to be converted to a better leaving group before substitution can occur.
electrostatic potential of methyl amine The image shows the electrostatic potential for methylammonium, CH3NH3+. The more red an area is, the higher the electron density and the more blue an area is, the lower the electron density. 
  • The ammonium N atom is a region of low electron density (blue) due to the positive charge.
  • Ammonium ions are not nucleophilic.
  • There is low electron density (blue) on H atom of the -NH3 group.
  • Removal of the proton regenerates the amine.
  • The -NH3 group is a potential leaving group.

Basicity:


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organic chemistry © Dr. Ian Hunt, Department of Chemistry University of Calgary