1. C. L. Bell, J. P. Shoffner and L. Bauer, Chem. and Ind., 1353 (1963).
2. J. A. Elvidge and L. M. Jackman, [J. Chem. Soc., 859 (1961)] have postulated that 2-pyridone possesses 36% of the aromaticity attributed to benzene, aromaticity being defined as the ability of an induced ring current to be sustained in a cyclic system due to the delocalization of the π-electrons. They measured the chemical shifts of C-methyl groups in a series of methyl substituted 2-pyridones and compared these to those of some non-aromatic models.
3. In a recent communication, J. A. Elvidge [Chem. Comm., 160 (1965)) has applied his method for the estimation of aromaticities of furan, thiophene and pyrrole.