How many signals would you expect to see in the 13C NMR spectrum of each of the following...

How many signals would you expect to see in the 13C NMR spectrum of each of the following compounds?

(a) Propylbenzene

(b) Isopropylbenzene

(c) 1,2,3-Trimethylbenzene

(d) 1,2,4-Trimethylbenzene

(e) 1,3,5-Trimethylbenzene

Sample Solution (a) The two ring carbons that are ortho to the propyl substituent are equivalent and so must have the same chemical shift. Similarly, the two ring carbons that are meta to the propyl group are equivalent to each other. The carbon atom para to the substituent is unique, as is the carbon that bears the substituent. Thus, there will be four signals for the ring carbons, designated w, x, y, and z in the structural formula. These four signals for the ring carbons added to those for the three nonequivalent carbons of the propyl group yield a total of seven signals.

Propylbenzene