Page 258 - Mechanism and Theory in Organic Chemistry
P. 258
Mechanisms Intermediate Between SN1 and SN2 247
N-.C distance
- increase decrease
Figure 5.9 A hypothetical free-energy surface for an SN2 reaction. Reaction starts at the
back left-hand corner and proceeds along the heavy line over the surface, with
simultaneous approach of N and departure of X, to the products at the front
right-hand corner. The transition state is marked by *.
decrease -
- increase
Figure 5.10 In the limiting SN1 process, the most favorable path is, first, rate-determining
breaking of the C-X bond by passing over the transition state *, to the inter-
mediate, N + C+ + X-; then, proceeding in another step over a second
barrier, *Q, to products.
