Page 399 - Advanced Organic Chemistry Part A - Structure and Mechanisms, 5th ed (2007) - Carey _ Sundberg

380
Y pK a
CHAPTER 3 4-CH 3 O 9.32
3-CH 3 O 9.04
Structural Effects on
Stability and Reactivity 4-CH 3 9.22
4-F 8.94
H 9.03
8.19
3-NO 2
8.14
4-NO 2
4-Cl 8.83
3-Cl 8.67
3.8. Write the rate law that would apply to the rate of product formation for each of
the following reaction mechanisms.
a. H H H
k 1 –
+
C C + R 3 N + R N H
3
Br Br k -1 Br Br
H
– k 2 –
H C C Br + Br
Br Br
k 3
+
H C C Br + R 3 N H C C N R 3
where the second step is rate-determining and the first step is an equilibrium

b. k 1
(CH ) CO C NO 2 (CH ) C+ + – O C NO
2
3 3
H O-acetone 3 3 2 2
2
(CH ) COH
3 3
k 2 O
H 2
) C+
(CH 3 3
–H +
k 3 (CH ) C=CH 2
3 2
where the competing product-forming steps are faster than the first step
Br
c. X + Br 2 k 1 X +
k –1 H

Br k
X + 2 +
X Br + H
H
k 3
Br – + Br 2
k –3

assuming that the σ complex is a steady state intermediate and that the final step is a rapid
–
equilibrium that converts some of the initial Br2 to unreactive Br3 . What is the form of the
rate expression if the intermediate of the first step goes on to product much faster than it
–
reverts to starting material and if the equilibrium constant for Br3 formation is large.