NAME: November 3, 2008
Chemistry 231 – Elementary Organic Chemistry
Take Home Quiz -- #6
1. (20 pts total) Consider the following S
N
2-type reaction between iodomethane and
ammonia:
CH
3
—I + :NH
3
[CH
3
—NH
3
]
+
+ I
-
a. (4 pts) Given that this is a second-order process (Hint: It is
a concerted process), write a reasonable rate expression
for the above reaction. Place your answer in the box
provided.
b. (8 pts) In the space provided below, draw a three-dimensional diagram showing
the transition state for the S
N
2-type reaction between iodomethane and
ammonia. Be certain to indicate both the geometry and bond angles at carbon in
your model.
c. (8 pts) Why do you think that this process proceeds by way of the S
N
2 reaction
mechanism? Be concise.
The electrophile is a methyl group which is expected to react fastest by
the S
N
2 mechanism. NH
3
is a small, basic nucleophile and I
-
, a weak
base, is an excellent leaving group. As well, the kinetics are observed to
be bimolecular. Taken together, these observations support that this
process proceeds by way of the S
N
2 reaction mechanism.
Rate=k[CH
3
I][NH
3
]
H
3
NC I
H
HH
δ
-
δ
+
δ
+
∠
H-C-N = 90°
∠
H-C-I = 90°
∠
H-C-H = 120°
sp
2
