Problem 10

C₃H₆O₂
Rule 2, omit O, gives C₆H₆
3 - 6/2 + 1 = 1 degree of unsaturation.
Look for 1 pi bond or aliphatic ring.

The band at 1716 indicates a carbonyl. The wide band from 3300-2500 is characteristic of the O-H stretch of carboxylic acids. The bands at 3000-2850 indicate C-H alkane stretches. The bands in the region 1320-1000 indicate the C-O stretch of carboxylic acids.

This is the structure. See if you can assign the peaks on your own.