A2 AQA CHEM4 3.4.7
- 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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