A2 AQA CHEM4 3.4.7

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  • Created by: Nuha
  • Created on: 23-04-14 12:54

3.4.7 Amines

Base properties (Brǿnsted-Lowry)

·         1o amine RNH2

·         2o amine R2NH (N-substituted amine)

·         3o amine R3N (N,N-substituted amine)

·         4o ammonium ion [R4N]+ (N,N,N-aminium ion)

·         NH3 and aliphatic amines can accept H+ ions due to their lp of e- and therefore act as Brǿnsted-Lowry bases but they all have different base strengths since the lp has different availabilities

  • Base strength increase from aromatic amines-->NH3-->aliphatic amines 


NH3 dissolves in water and accepts H+

·         NH3 + H2O <-->  NH4+ + OH-

·         The equilibrium lies to the left so NH3 is a weak base

·         Roughly pH 11.63

1o aliphatic amines

·         CH3NH2 + H2O <-->  CH3NH3+ + OH-

·         The lp of e- on the N means it can accept H+ ions

·         Stronger base than NH3, roughly pH 12.32

·         This is because the alkyl groups are e- releasing groups and they increase the electron density of the nitrogen atom via the positive inductive effect. This makes the lp of e- on the N atom more available to accept H+ by forming a co-ordinate bond with it

o   The more alkyl groups there are, the more available the lp is and so the higher the…

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