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200 RADICAL REACTIONS
QUIZ Use the single-bond dissociation energies of Table 10.1 (page 202):
10.1 On the basis of Table 10.1, what is the order of decreasing stability of the radicals,
?
> >
HC C
HC C(a)
CHCH2CH2 CH
CH2 CH
CH2
CHCH2CH2
> >HC C(b) CH2 CH
CH2 CH
CHCH2CH2
>> HC C
HC C
(c) CHCH2CH2
CH2 CH> >(d) CHCH2CH2
HC CCH2 CH > >(e) CHCH2CH2
10.2 In the radical chlorination of methane, one propagation step is shown as
Cl CH4 HCl CH3+ +
Why do we eliminate the possibility that this step goes as shown below?
Cl CH4 CH3Cl H+ +
(a) Because in the next propagation step, H· would have to react with Cl2 to form Cl· and
HCl; this reaction is not feasible.
(b) Because this alternative step has a more endothermic �H ◦ than the first.
(c) Because free hydrogen atoms cannot exist.
(d) Because this alternative step is not consistent with the high photochemical efficiency
of this reaction.
10.3 Pure (S)-CH3CH2CHBrCH3 is subjected to monobromination to form several isomers of
C4H8Br2. Which of the following is not produced?
(a) (b) (c)
(d) (e)
Br
Br H
H
Br Br
Br
H Br
HH
Br H
Br
H Br
Br
10.4 Using the data of Table 10.1, calculate the heat of reaction, �H ◦, of the reaction,
+ +CH3CH3 HBrBr2 Br
(a) 47 kJ mol−1 (b) −47 kJ mol−1 (c) 1275 kJ mol−1
(d) −1275 kJ mol−1 (e) −157 kJ mol−1