Mass-spectrometric study of ring-chain tautomerism in a series of substituted 4-hydroxyhexahydropyrimidine-2-thiones

In order to investigate the ring-chain tautomerism of substituted 4-hydroxyhexahydropyrimidine-2-thiones the mass spectra of a series of compounds of this group were studied. It is shown that equilibrium exists between the cyclic hydroxy form and the acyclic oxo form, which belongs to the oxoalkylthiourea class, in a series of 3-alkyl(aryl)-4,6,6-trimethyl derivatives in the gas phase. The mass spectra of these compounds contain intense peaks of M-18]⁺ and M-33]⁺ ions, which are formed as a result of the successive elimination of a water molecule and a methyl radical by the molecular ions. The fragmentation of 3-alkyl-4,5-dimethyl derivatives takes place from the open oxo form of the molecular ion with detachment of the terminal groups.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1273–1278, September, 1983.