The labels on a shipment of the five chemicals A - E below were washed off by ac

Question

The labels on a shipment of the five chemicals A - E below were washed off by accident when the delivery truck went through a truckwash with the doors open. A clever student took infrared spectra of each of the resulting unknowns. Unknown #1 had a strong, broad IR absorption at 3400-3600 cm-1, and no absorptions between 1600 and 2900 cm-1. Unknown #2 had a strong absorption at 1680 cm-1 and no absorptions above 3100 cm-1. What are the structures of unknowns 1 and 2? Unknown #1 A B C D E Unknown #2 A B C D E

Explanation / Answer

unknown #1 ---> B note: 3400 -3600 cm-1 ---> OH stretch no peak between 1600 - 2900 cm-1 rule out the presence of C=O group (1600 - 1800 cm-1). Thus, A, C, D, E are ruled out. unknown # 2----> C note: > 3100 cm-1 no absorption means that it has peaks between 3100 and 3000 cm-1. This indicates the presence of C=C-H. 1680 cm-1 corresponds to C=O group. Thus, answer C is correct.

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