Bruice - Chimica Organica

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452 Chapter 13
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69. The broad absorption band at 3300 cm -1 indicates that the compound has an OH group. The absorption
bands at 2900 cm - 1 indicate that the compound has hydrogens attached to an sp 3 carbon. The compound,
therefore, is benzyl alcohol.
70. In an acidic solution, the three benzene rings are isolated from one another, so phenolphthalein is colorless.
In a basic solution, loss of the proton from one of the OH groups causes the five-membered ring to open.
As a result, the number of conjugated double bonds increases, causing the solution to become colored.
C −
−
C O
O
O
C
O
O
OH
HO
O H
OH
71. a. The absorption bands at 1720 cm- 1 and 2700 cm- 1 (C—H of an aldehyde) indicate that the com-
pound is an aldehyde. The absence of an absorption band at 1600 cm- 1 rules out the aldehyde with
the benzene ring. Therefore, it must be the other aldehyde.
H
O
b. The absorption bands at 3350 cm- 1 and 3200 cm- 1 indicate that the compound is an amide
(nitrogen–hydrogen stretch). The absence of an absorption band at 3050 cm - 1 indicates that the com-
pound does not have hydrogens bonded to sp2 carbons. Therefore, it is not the amide that has a benzene
ring. Thus, it must be the other amide.
NH2
O
c. The absence of absorption bands at 1600 cm -1 and 1500 cm- 1 indicates that the compound does
not have a benzene ring. Therefore, it must be the ketone. This is confirmed by the absence of an
absorption band at 1380 cm -1, indicating that the compound does not have a methyl group.
O