Problem 9

C₁₁H₁₄O₂
Rule 2, omit O, gives C₁₁H₁₄
11 - 14/2 + 1 = 5 degrees of unsaturation.
Look for an aromatic ring, plus 1 other pi bond or aliphatic ring.

The band at 1603 or 1894 might indicate a carbonyl outside the normal range; the small peak around 1800 indicates it may be an aldehyde. The band at 1510 is an aromatic ring. The bands at 3000-2850 indicate C-H alkane stretches.

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

Based on what is covered, you shouldn't need to distinguish between B and C, but you should be able to tell that the ring is para-substituted.