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Variations of Tautomeric Preferences in Histamine Monocation-Ab initio Studies for "Essential" and "Scorpio" Conformations from the Gas Phase to Aqueous Solution

Darowska M., Raczyńska E. D.

Polish Journal of Chemistry

2002

Vol. 76 / nr 7

1027-1035

The polarizable continuum model (PCM) for geometries optimized at the RHF/6-31G* was applied to study the variations of the tautomeric preferences in the histamine monocation from the gas phase to aqueous solution. Seven solvents of different polarities (from cyclohexane to water) were chosen and calculations performed. A change of the tautomeric preference takes place already in apolar solvents containing heteroatoms. The ring N-aza protonated form (ImH+) is only favoured in the gas phase and cyclohexane,oe benzene, CCl4. The chain N-amino protonated form (AmH+-T1) predominates in other solvents: CHCl3, THF, acetone, water.

Prototropic Tautomerism in 2- and 4-Hydroxypyridines : Halogen Substituent Effects in the Gas Phase Calculated by Semiempirical (AM1) Method

Raczyńska E.

Polish Journal of Chemistry

1999

Vol. 73, nr 11

1863-1876

Tautomeric equilibrium constants were calculated in the gas phase for unsubstituted, mono- and tetrahalogenated 4-hydroxypyridines and for unsubstituted, mono-, di- and tetrahalogenated 4-hydroxypyridines using semiempirical method. Influence of position of halogen on the pK is studied and compared with that found previously in solution.