Organic Chemistry

PROBLEM 22

Which alkyl halide would you expect to be more reactive in an reaction with a given

nucleophile? In each case, you can assume that both alkyl halides have the same stability.

a. or

b. or

c.

d.

e.

f.

g.

PROBLEM 23

For each of the pairs in Problem 22, which compound would be more reactive in an

reaction?

PROBLEM 24

Show the configuration of the products obtained from the following reaction:

a. under conditions that favor an reaction

b. under conditions that favor an reaction

10.9 Competition Between and Reactions

The characteristics of and reactions are summarized in Table 10.5. Remem-
ber that the “ 2 ”in and the “ 1 ”in refer to the molecularity—how many
molecules are involved in the rate-determining step. Thus, the rate-determining step of
an SN 2 reaction is bimolecular, whereas the rate-determining step of an SN 1 reaction is

“SN 2 ” “SN 1 ”

SN 2 SN 1

SN 2 SN 1

CH 3 OH

CH 3 CH CHCH 2 Br + CH 3 O−

SN 1

SN 2

SN 1

CH 3 CH CCH 3 or

Br

CH 3 CH CHCHCH 3

Br

CH 2 Br or Br

CH 2 CH 2 Br or CH 2 CHCH 3

Br

CH 3 CH 2 CH 2 CHBr

CH 3

CH 3 CH 2 CHCH 2 Br

CH 3

or

CH 3 CH 2 CHBr or

CH 3

CH 3 CH 2 CHBr

CH 2 CH 3

CH 3 CH 2 CH 2 Cl CH 3 OCH 2 Cl

CH 3 CH 2 CH 2 Br CH 3 CH 2 CH 2 I

SN 2

Section 10.9 Competition Between SN 2 and SN 1 Reactions 385

Table 10.5 Comparison of SN 2 and SN 1 Reactions

A one-step mechanism A stepwise mechanism that forms a carbocation

intermediate

A bimolecular rate-determining A unimolecular rate-determining

step step

No carbocation rearrangements Carbocation rearrangements

Product has inverted configuration Products have both retained and inverted

relative to the reactant configurations relative to the reactant

Reactivity order: Reactivity order:

methyl 71 ° 72 ° 73 ° 3 ° 72 ° 71 ° 7 methyl

SN 2 SN 1