Chemistry Reference
In-Depth Information
S
N
1
Nu
−
H
2
CCH
C
H
2
Nu
H
2
CCH
C
H
2
Cl
H
2
CCH
C
H
2
allyl chloride
attack of nucleophile onto
either terminal carbon
resonance-stabilized
allylic cation
Nu
−
H
2
CCH
C
H
2
NuH
2
CCH
C
H
2
S
N
1
Nu
−
Cl
Nu
with a non-symmetrical allylic system,
two different products would be formed
Nu
−
Nu
Note that with allyl derivatives there is potential for
the nucleophile to react with the different resonance
forms, perhaps leading to a mixture of products. This
is not the case with the benzylic substrates, since only
the benzylic product is formed; addition to the ring
would destroy the stability conferred by aromaticity.
S
N
1
CH
2
Cl
CH
2
CH
2
CH
2
benzyl chloride
resonance-stabilized
benzylic cation
Nu
−
only the benzylic product is
formed; addition to the ring
would destroy aromaticity
CH
2
Nu
One of the most stable carbocation structures is the
triphenylmethyl cation (
trityl cation
). In this struc-
ture, the positive charge is stabilized by resonance
employing all three rings. Trityl chloride ionizes read-
ily, and can capture an available nucleophile.
S
N
1
NuH
many resonance
structures
Cl
Nu
trityl chloride
trityl cation
