1. The manifold possibilities for tautomerism in seven-membered heterocyclic systems are virtually unexplored; cf., however, Rees A.H. J. Chem. Soc. 3111 1959
2. Within these limitations we have attempted to include references to all relevant work. However, since it is difficult to locate papers dealing only incidentally with tautomerism, there are undoubtedly pertinent references which have been missed. We would be most grateful if these omissions were brought to our attention.
3. “Structure and Mechanism in Organic Chemistry,”;Ingold,1953
4. “Tautomerism.”;Baker,1934