Figure S1. DFT-calculated low-energy structures and energies for compound (aS)-1. Figure S2. DFT-calculated lowest-energy structure for compound (aS)-1 in the " ND " tautomeric form.

A series of derivatives of 2-hetaryl-1,3-tropolone (β-tropolone) was prepared by the acid-catalyzed reaction of 2-methylbenzoxazoles, 2-methylbenzothiazoles and 2,3,3-trimethylindoline with 3,4,5,6-tetrachloro-1,2-benzoquinone. The molecular structures of the three representative compounds were determined by X-ray crystallography. In crystal and (as shown by the DFT PBE0/6-311+G** calculations)...

Hydroxyurea (Hy) in aqueous solutions has several tautomeric forms due to the formation of a >N-OH bond. The azometinic group >C=Nis present in all these tautomeric forms. The structural forms influence the hydrophil-lipophil character of Hy and it determines the complexing of the Fe(II) ions, thus explaining the appearance of anemia, due to the treatment with hydroxyurea. The paper presents a ...

A combined Monte Carlo and quantum mechanical study was carried out to analyze the tautomeric equilibrium of 2-mercaptopyrimidine in the gas phase and in aqueous solution. Second- and fourth-order Møller-Plesset perturbation theory calculations indicate that in the gas phase thiol (Pym-SH) is more stable than the thione (Pym-NH) by ca. 8 kcal/mol. In aqueous solution, thermodynamic perturbation...

A series of new bis azo dyes were synthesized starting from aromatic diamine with S/SO2 bridges and cyclic-1,3-dicarbonyl groups; contain active methylene group, namely; 3,3-dimethyl-1,5-cyclohexadione (dimedone), 1,3-cyclohexadione 2,2-dimethyl-1,3-dioxane-4,6-dione to give 1-6. Whether the reaction is complete purity compounds checked TLC. The structure newly synthezed was investigated by usi...

N-(pyridin-2-yl)thiazol-2-amine is a versatile chemical functional unit present in many therapeutically important species. Quantum chemical analysis shows that there are six competitive isomeric structures possible for this class of compounds within a relative energy difference of ∼4 kcal/mol. Some of the isomeric structures possess divalent N(I) character. There appears to be a competition bet...

We investigated how many cases of the same chemical sold as different products (at possibly different prices) occurred in a prototypical large aggregated database and simultaneously tested the tautomerism definitions in the chemoinformatics toolkit CACTVS. We applied the standard CACTVS tautomeric transforms plus a set of recently developed ring-chain transforms to the Aldrich Market Select (AM...

Reaction enthalpies and reaction volumes of proton-transfer reactions in aqueous solutions of 3-hydroxypyridine have been estimated by measuring UV-visible absorption spectra at different temperatures, pressures, and pH values. Using these results together with published thermodynamic and kinetic data, we have simulated the relaxation spectrum of the proton-transfer reactions of 3-hydroxypyridi...

The reliability of three popular semiempirical quantum chemical methods (AMI, PM3, MNDO) for the treatment of tautomeric equilibria is tested in a series of five-membered nitrogen heterocycles. The known flaw of M N D O to overestimate the stability of compounds with two or more adjacent pyridine-like lone pairs is also present in AMI and to a somewhat lesser extent in PM3. Tautomeric species d...

Heterocyclic nucleic acid bases and their analogs can adopt multiple tautomeric forms due to the presence of multiple solvent-exchangeable protons. In DNA, spontaneous formation of minor tautomers has been speculated to contribute to mutagenic mispairings during DNA replication, whereas in RNA, minor tautomeric forms have been proposed to enhance the structural and functional diversity of RNA e...