Abstract
Carbon-13 nuclear magnetic resonance spectra of six barbituric acid derivatives were measured. In addition, extended Huckel calculations were carried out on 18 barbituric acid derivatives, and the following examinations were made. (1) Shielding constants, based on Pople's theory, were calculated. (2) Additive equations on atomic populations of sp3-hybridized carbons were calculated. (3) Monoionized state of 5-ethylbarbituric acid was estimated from the standpoint of total energy.
