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Chapter 28 853
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d.
D
D
H
H
hv
D
H
D
H
H
H
H
H
CH
3
CH
3
CH
3
CH
3
e.
f.
g.
hv
H H
H
3
C
H
3
C
h.
24.
Because the compound has an odd number of
p
bonds, it undergoes disrotatory ring closure under thermal
conditions and conrotatory ring closure under photochemical conditions.
In the compounds in which the two methyl substituents point in opposite directions, the substituents will
be cis in the ring-closed product when ring closure is disrotatory and trans in the ring-closed product when
ring closure is conrotatory.
In the compounds in which the two methyl substituents point in the same direction, the substituents will
be trans in the ring-closed product when ring closure is disrotatory and cis in the ring-closed product when
ring closure is conrotatory.
a.
CH
2
CH
3
CH
2
CH
3
b.
CH
2
CH
3
CH
2
CH
3
CH
3
CH
2
CH
3
CH
2
+
c.
CH
2
CH
3
CH
2
CH
3
CH
3
CH
2
CH
3
CH
2
+
d.
CH
2
CH
3
CH
2
CH
3