CH 6-2: SN2 Reaction-II

1
CH 6-2 SN2 Reaction-II Stereochemistry in The
SN2 ReactionA Stereospecific Reaction
(S)
(R)
Inversion of Configuration..Why?
2
Example SN2 Reaction?
(R)
(S)

• What is the configuration at the chiral center in
  reactant and product?

• Is there an Inversion of Configuration?

• Is this an SN2 reaction?

3
Re-cap The SN2 Substitution Reaction

• A bimolecular, concerted mechanism

• Energy Diagram minimum of one step (one T.S.)

• Pentavalent Carbon in the T.S. crowded T.S.

• Nuc grabs the electrophilic carbon 180o
  opposite the Lg.

• Stereospecific reaction inversion of
  configuration

4
Alkyl Halide Structure in SN2 Reactions

• What was the significance of the SN2 Transition
  State?

CROWDED!

• How would large R groups effect the reaction?

• Rank the following substrates in order of SN2
  reactivity

Methyl gtgtgt 1o gt 2o
gtgtgtgtgt 3o (NR)
5
Alkyl Halide Structure in SN2 Reactions
Methyl gtgtgt 1o gt 2o gtgtgtgtgtgtgtgtgtgtgtgtgt 3o
(NR)
6
Alkyl Halide Structure in SN2 Reactions

• Halogens bonded to sp2 carbon (vinyl and phenyl
  halides) do not undergo substitution

WHY NOT?