[Big-Daddy]

Am I correct to think that phenylbutazone (Google) has 10 distinct peaks on a ¹³C NMR spectrum?

A further problem: from the structure of phenylbutazone (M_r=308), I am to find a metabolite structure which has M_r=324, such that there are 15 peaks on a ¹³C NMR spectrum of the metabolite. Am I right to think that the correct solution is to replace an H substituted on one of the phenyl groups with OH (+16 change in M_r as required, and the symmetry is now destroyed)?

[TwistedConf]

Sounds like you're on the right track.  Have you looked up the actual spectrum of the compound? Shouldn't be hard to find.

Clearly, the number of product peaks will help determine where you stick that OH.