Infrared spectra and ultraviolet characteristics for nine 5,5-disubstituted 1:3-dimethyl barbituric acids are presented. X-ray diffraction powder data are given for 5 of these compounds.
Jane M. Manson and J. A. R. Cloutier, "Physico-Chemical Characterization of Some 5,5-Disubstituted 1:3-Dimethyl Barbituric Acids," Appl. Spectrosc. 15, 77-79 (1961)