THE TAUTOMERIC EQUILIBRIA OF THIO ANALOGS OF NUCLEIC-ACID BASES .3. ULTRAVIOLET PHOTOELECTRON-SPECTRA OF 2-THIOURACIL AND ITS METHYL-DERIVATIVES

The photoelectron spectra of 2-thiouracil and four monoalkyl and four dimethyl derivatives were recorded using He(I) and He(II) excitations. The assignments of the photoelectron bands were based on relative band intensity variations, on the results of AM1 calculations, and by comparisons with uracil and its methyl derivatives. The photoelectron spectrum of 2-methyl-2-thiouracil gave evidence of two forms in tautomeric equilibrium in the gas phase.