The possible thione–thiol tautomerism of 2- and 4-mercaptopyridines, 2-mercaptopyrimidine, and 4,6-dimethyl-2-mercaptopyrimidine in solution is studied by means of absorption (UV–VIS) spectroscopy. In accordance with earlier observations, polar solvents and self-association shift the apparent tautomeric equilibrium significantly towards the thione form. In dilute solutions of nonpolar solvents the thiol form predominates. On standing, significant changes are observed in the absorption spectra of these tautomeric compounds in ethanol, dioxane, and water. The time course of the tautomerization, followed spectrophotometrically, reveals quantitative transformation of the thiol form to the corresponding symmetrical disulfides. The influence of concentration, temperature, and irradiation with indirect sunlight are discussed. This thione–disulfide process is reversible in water, starting either from the tautomeric thione or from its symmetrical disulfide, implying a possible importance in biological systems. Keywords: thione–thiol tautomerism, absorption spectra, thiol–disulfide oxidation, mercaptopyridines and pyrimidines.

This paper documents the speed of evolution (or lack thereof) of a range of values and beliefs of different generations of US immigrants, and interprets the evidence in the light of a model of socialization and identity choice. Convergence to the norm differs greatly across cultural attitudes. Moreover, results obtained studying higher generation immigrants differ from those found when the analysis is limited to the second generation and imply a lesser degree of persistence than previously thought. Persistence is also culture specific, in the sense that the country of origin of one's ancestors matters for the pattern of generational convergence.

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