Interactions | Reactions | Processes

Classified as: Ambidentate Behaviour: Elimination vs Substitution 2

According to Pearsons hard soft [Lewis] acid base principle, hard Lewis acids have a strong affinity for hard Lewis bases and soft Lewis acids have a strong affinity for soft Lewis bases.

Hard alkoxide ion preferentially abstracts a hard proton, so initiating E2 elimination, whereas soft nucleophilic malonate carbanion preferentially displaces soft bromide ion nucleofuge. (Note that the pKa values of the conjugate acids, ethanol and diethyl malonate, a similar, around 16.)

Note that while hard vs soft comparisons can be made for carefully selected pairs of species and/or reactive centres, the HSAB analysis is NOT general. For more information look in the Chemogenesis webbook section on Pearson's HSAB principle.
(CH3)2CHBr
  +  
         
  +  
Br–

Go To Reaction Data Page
(CH3)2CHBr
  +  
CH3CH2O–
         
CH3–CH=CH2
  +  
Br–
  +  
CH3CH2OH

Go To Reaction Data Page

© Mark R. Leach 1999 –

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