Bruice - Chimica Organica

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450 Chapter 13
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b. The absorption band at 1685 cm- 1 indicates a carbon–oxygen double bond. The absence of a
strong and broad absorption band at 3000 cm - 1 rules out the carboxylic acid, and the absence of an
absorption band at 2700 cm- 1 rules out the aldehyde. Therefore, it must be one of the ketones. The
ketone with the conjugated carbonyl group would be expected to show a C “ O stretch at 1685 cm - 1,
whereas the ketone with the isolated carbonyl group would show a C “ O stretch at 1720 cm - 1.
Thus, the compound is the ketone with the conjugated carbonyl group.
O
c. The absorption band at 1700 cm - 1 indicates a carbon–oxygen double bond. The absence of an
absorption band at 1600 cm -1 rules out the ketones with the benzene or cyclohexene rings. The
absence of absorption bands at 2100 cm - 1 and 3300 cm- 1 rules out the ketone with the carbon–
carbon triple bond. Therefore, it must be 4-ethylcyclohexanone.
O
63. The absorption bands at 2700 cm -1 for the aldehyde hydrogen and at 1380 cm - 1 for the methyl group
will distinguish the compounds.
A will have the band at 2700 cm -1 but not the one at 1380 cm - 1.
B will have the band at 1380 cm -1 but not the one at 2700 cm -1.
C will have the band at both 2700 cm- 1 and 1380 cm - 1.
64. 1-Hexyne will show absorption bands at 3300 cm- 1 for a hydrogen bonded to an sp carbon and at
2100 cm -1 for the triple bond.
CH 3CH2 CH 2CH 2C CH
1-hexyne
2-Hexyne will show the absorption band at 2100 cm -1 but not the one at 3300 cm - 1.
CH3 CH2CH2C CCH3
3-Hexyne will not show the absorption band at either 3300 cm- 1 or 2100 cm- 1 (there is no change in
dipole moment when the C C stretches).