Chemistry Reference
In-Depth Information
6.21
a.
Sodium cyanide is a strong, anionic nucleophile. Thus the mechanism is S
N
2
and the reactivity order of the halides is primary > secondary > tertiary.
Therefore,
(CH
3
)
2
CHCH
2
Br > CH
3
CH(Br)CH
2
CH
3
>> (CH
3
)
3
CBr
b.
With 50% aqueous acetone, there is a weak nucleophile (H
2
O) and a highly
polar reaction medium favoring ionization, or the S
N
1 mechanism. In this
mechanism, the reactivity order of alkyl halides is tertiary > secondary >
primary. Therefore,
(CH
3
)
3
CBr >> CH
3
CH(Br)CH
2
CH
3
>> (CH
3
)
2
CHCH
2
Br
6.22
a.
The halide is tertiary, and the nucleophile is a relatively weak base. Hence
the predominant mechanism is S
N
1:
H
3
C
Cl
H
3
C
OCH
2
CH
3
+CH
3
CH
2
OH
+
l
Some E1 reaction may occur in competition with S
N
1, giving mainly the
product with the double bond in the ring:
CH
3
CH
2
H
3
C
Cl
E1
+
+
+
HCl
CH
3
CH
2
OH
major
minor
However, the main product will be the ether (S
N
1).
b.
The nucleophile in this case is stronger, but the S
N
2 process is not possible
because the alkyl halide is tertiary. This nucleophile is also a strong base.
Therefore, an E2 reaction will be preferred.
CH
3
H
3
C
Cl
H
E2
Cl
_
_
+
3
CH
2
O
+
CH
3
CH
2
OH
+
or
CH
2
Cl
CH
2
H
E2
CH
3
CH
2
O
_
l
_
+
+
+
CH
3
CH
2
OH
The predominant product is 1-methylcyclohexene, the more stable of the two
possible alkenes.
