Chapter 27.1, Problem 3P

Interpretation Introduction

Interpretation:

The given compounds caffeine and theobromine are to be classified as pyrimidine and purine. The fact that one of these two cannot isomerize to an enolic form, while two different enols are possible for the other is to be explained. The structural formulas for the possible enols is to be written.

Concept introduction:

The purines and pyrimidines are nitrogen bases that constitute the structural unit of nucleic acids.

Both purines and pyrimidines are nitrogen containing heterocyclic aromatic compounds.

The structures of pyrimidine and purine are shown below:

The structure of pyrimidine resembles that of benzene and pyridine having two nitrogen atoms.

In the structure of purine, the prymidine ring is fused with imidazole ring and has four nitrogen atoms.

The structure having an acidic hydrogen at alpha position to ketone (carbonyl carbon) can tautomerize into a keto-enol form.