Chemistry Reference
In-Depth Information
3. For each of the following reactions, determine which will proceed via an S
N
1oranS
N
2
mechanism. In cases where both may be applicable, list appropriate reaction conditions
(e.g., solvents, reagents) that would favor S
N
1overS
N
2 and vice versa. Explain
your answers.
a.
b.
c.
4. In studying 1,2-alkyl and hydride shifts, we explored the observation that shifts will
not occur unless the newly formed carbocation is more stable than the starting carbo-
cation. Additionally, as illustrated in Figure 5.12, these shifts were explained using
hyperconjugation, thus requiring that the orbital containing the positive charge
and the bond containing the shifting group lie within the same plane. This is
necessary in order to allow sufficient orbital overlap for the shift to take place.
In addition to 1,2-shifts, which occur between adjacent bonds, other shifts are possible
where the migrating group apparently moves across space. As with 1,2-shifts, these
additional shifts can only occur when the positively charged empty p orbital lies
within the same plane as the bond containing the migrating group, thus allowing
sufficient orbital overlap. With this in mind, explain the following 1,5-hydride shift.
(Hint: Consider different structural conformations. You may want to use models.)
Asterisk (
) marks enrichment with
13
C.
