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200 Chapter 5
Copyright © 2017 Pearson Education, Inc.
47.
First draw the structures so you can see the number of alkyl groups bonded to the
sp
2
carbons:
CH
3
CH CCHCH
2
CH
3
CH
3
CH
3
3,4-dimethyl-2-hexene
CH
3
C CCH
2
CH
2
CH
3
2,3-dimethyl-2-hexene
CH
3
CH
3
CH
3
CH CHCHCHCH
3
4,5-dimethyl-2-hexene
CH
3
CH
3
a.
2,3-Dimethyl-2-hexene is the most stable of the three alkenes because it has the greatest number of
alkyl substituents bonded to the
sp
2
carbons.
b.
4,5-Dimethyl-2-hexene has the fewest alkyl substituents bonded to the
sp
2
carbons, making it the least
stable of the three alkenes. It, therefore, has the greatest heat of hydrogenation.
c.
Because it is the most stable, 2,3-dimethyl-2-hexene has the smallest heat of hydrogenation.
48.
H O H C
H
H
C H
H
Br
C
H
H
C
H
H
+
H
2
O
+
Br
−
+
−
49.
50.
∆
G
°
=
-
RT
ln
K
eq
ln
K
eq
=
-
∆
G
°
>
RT
ln
K
eq
=
-
∆
G
°
>
0.59 kcal
>
mol
a.
ln
K
eq
=
-
2.72
>
0.59 kcal
>
mol
ln
K
eq
=
-
4.6
K
eq
=
3
B
4 > 3
A
4
=
0.01
b.
ln
K
eq
=
-
0.65
>
0.59 kcal
>
mol
ln
K
eq
=
-
1.10
K
eq
=
3
B
4 > 3
A
4
=
0.33
c.
ln
K
eq
=
2.72
>
0.59 kcal
>
mol
ln
K
eq
=
4.6
K
eq
=
3
B
4 > 3
A
4
=
100
d.
ln
K
eq
=
0.65
>
0.59 kcal
>
mol
ln
K
eq
=
1.10
K
eq
=
3
B
4 > 3
A
4
=
3.0
51.
a.
The C
¬
Cl bond is a stronger bond because Cl uses a 3
sp
3
orbital to overlap the 2
sp
3
orbital of carbon,
whereas Br uses a 4
sp
3
orbital. A 4
sp
3
has a greater volume than a 3
sp
3
and, therefore, has less electron
density in the region of orbital-orbital overlap, so it forms a weaker bond.
b.
The Br
¬
Br bond is a stronger bond because Br uses a 4
sp
3
orbital to overlap the 4
sp
3
orbital of the
other bromine, whereas I uses a 5
sp
3
orbital. A 5
sp
3
has a greater volume than a 4
sp
3
and, therefore,
has less electron density in the region of orbital–orbital overlap, so it forms a weaker bond.
46.
a.
a. the most stable because it has three alkyl groups attached to its
sp
2
carbons.
b.
d., e., and f. are the least stable because the two alkyl groups in d. and e. are on the same
sp
2
carbon,
and the two alkyl groups in f. are cis.