Nucleophilic substitution reactions

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Nucleophilic substitution reactions

• SN1 and SN2

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Nature of nucleophiles in SN2 reactions

• Common nucleophiles, include NH3, CN-, H2O and
  OH-.

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SN1
4
SN2
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• nucleophilicity is the affinity of a species for
  the slightly positively charged carbon atom of
  the CX bond
• Less electronegative atoms will be better
  nucleophiles (better Lewis Bases)

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The nature of the leaving group in SN1 and SN2
reactions

• Two factors may be considered
• The greater the polarity of the CX bond
• The strength of the CX bond

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Steric Hindrance

• 30 react with SN1 mechanism, 10 with SN2 and 20
  can undergo both

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• 30 carbocations are stabilised by inductive
  effect of methyl groups (SN1)
• Bond geometry is more stable in carbocation
  (tetrahedral ? trigonal planar)
• Steric hindrance for SN2
• Because SN1 reactions happen faster than SN2, the
  order of reaction rate is
• 30 gt 20 gt 10

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