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Solutions for The Study of Chemical Reactions
C
CH3
H
CH2CH3CH3
HH
H
H
H
H H
H
H
H
H
H
H
HH
H
H
H
H H
H
H
H
H
CH3 C CH3
H
CH3
OR
H H
HH
H
H
H
H
H
H
H
H
CH3CH2CH2CH319
2°
2°
1°
1°1°1°1°
1°1°
3°3°
3°
3°all are 2° H
2°
1°
(e)
(d)
(c)(b)(a)
all are 2° H except at bridgehead (labeled 3°)
all are 2° H
20 ∆H° for abstraction of a 1° H from both ethane and propane are + 410 kJ/mole ( + 98 kcal/mole). It is 
reasonable to use this same value for abstraction of the 1° H in isobutane.
3° H abstraction
Cl • + +
∆H° = + 381 kJ/mole ( + 91 kcal/mole)
∆H° = – 431 kJ/mole ( – 103 kcal/mole)
∆H° = − 50 kJ/mole ( −12 kcal/mole)
break 3° H–C(CH3)3
make H–Cl
overall 3° H abstraction
Cl • + +
∆H° = + 410 kJ/mole ( + 98 kcal/mole)
∆H° = – 431 kJ/mole ( – 103 kcal/mole)
∆H° = − 21 kJ/mole ( − 5 kcal/mole)
break 1° H–CH2CH(CH3)2
make H–Cl
overall 1° H abstraction
1° H abstraction
C
CH3
H
CH3CH2 H Cl • CH2 C CH3
CH3
H
H
C
CH3
H
CH3CH3 H Cl CH3 C CH3
CH3
CH2H C CH3
H
CH3
3° radical;
∆H° = – 50 kJ/mole (− 12 kcal/mole)
1° radical; 
∆H° = – 21 kJ/mole (− 5 kcal/mole)en
er
gy
reaction coordinate
Cl • +
Since ∆H° for forming the 3° radical is more negative than ∆H° for forming the 1° radical, it is reasonable 
to infer that the activation energy leading to the 3° radical is lower than the activation energy leading to the 
1° radical.
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