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Chapter 28 857
Copyright © 2017 Pearson Education, Inc.
The second compound can undergo the 1,3-methyl group migration that the first compound undergoes, and
the
sec
-butyl group can also undergo a [1,3] sigmatropic rearrangement. The migrating
sec
-butyl group
will have its configuration inverted due to the antarafacial nature of the rearrangement.
H
3
C
H
C
CH
3
H
3
C
CH
3
H
CH
2
CH
3
1,3-
sec
-butyl
group migration
CH
3
H
3
C
C
H
H
3
C
H
3
C
1,3-methyl
group migration
H
3
C
H
C
CH
3
H
CH
2
CH
3
CH
3
H
3
C
CH
2
CH
3
34.
An infrared absorption band is indicative of a carbonyl group. A [3,3] sigmatropic rearrangement of the
reactant leads to a compound with two enolic groups. Tautomerization of the enols results in keto groups.
The keto carbonyl groups give the absorbance at 1715 cm
-
1
.
CH
3
OH
CH
3
OH
OH
CH
3
CH
3
OH
tautomerization
CH
3
CCH
2
CH
2
CH
2
CH
2
CCH
3
O
O
35.
The reaction is a [1,7] sigmatropic rearrangement. Because the reaction involves four pairs of electrons,
antarafacial rearrangement occurs. Therefore, when H migrates, because it is above the plane of the reactant
molecule, it ends up below the plane of the product molecule. When D migrates, because it is below the
plane of the reactant molecule, it ends up above the plane of the product molecule.
CH
3
H D
D
CH
3
H
H
CH
3
D