Problems 357
- The deuterium kinetic isotope effect for chlorination of an alkane is defined in the following equation:
Predict whether chlorination or bromination would have a greater deuterium kinetic isotope effect.
- a. How many monobromination products would be obtained from the radical bromination of methylcyclohexane?
Ignore stereoisomers.
b. Which product would be obtained in greatest yield? Explain.
c. How many monobromination products would be obtained if all stereoisomers are included?
- a. Propose a mechanism for the following reaction:
b. Given that the value for the reaction is and the bond dissociation energies for the and
bonds are 101, 82, and 102 kcal mol, respectively, calculate the bond dissociation energy of the bond.
c. Which set of propagation steps is more likely to occur?
- a. Calculate the value for the following reaction:
b. Calculate the sum of the values for the following two propagation steps:
c. Why do both calculations give you the same value of
- A possible alternative mechanism to that shown in Problem 24 for the monochlorination of methane would involve the following
propagation steps:
How do you know that the reaction does not take place by this mechanism?
- Explain why the rate of bromination of methane is decreased if HBr is added to the reaction mixture.
CH 3 H
H +
Cl
Cl
+
H
CH 3
Cl
Cl H
+ Cl
+
Cl
¢H°?
CH 3 HH+ Cl CH 3 + Cl
CH 3 ++Cl Cl CH 3 Cl Cl
¢H°
CH 4 + Cl 2 CH 3 Cl + HCl
h
¢H°
O¬H > O¬Cl
¢H° - 42 kcal>mol C¬H,C¬Cl,
∆
C
CH 3
CH 3
CH 3 CH 3 + CH 3 OCl C
CH 3
CH 3
CH 3 CH 2 Cl + CH 3 OH
= rate of homolytic cleavage of a C
rate of homolytic cleavage of a C
H bond by Cl
D bond by Cl
deuterium kinetic
isotope effect
