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Composition of Tautomeric Mixtures Studied by Nitrogen Chemical Shifts and Ab Initio Molecular Orbital Calculations

Wiench J. W., Koprowski M., Stefaniak L., Webb G. A.

Polish Journal of Chemistry

2002

Vol. 76 / nr 4

525-536

Some nitrogen and carbon chemical shifts and ab initio Gauge Invariant Atomic Orbitals - Coupled-Perturbed Hartree-Fock (GIAO-CPHF) calculations are reported for benzotriazole 1, 5-nitrobenzimidazole 2, 5-nitrobenzotriazole 3, 4-nitrobenzotriazole 4, and N-methyl derivatives of compounds 1-3. A good correlation is found between the calculated and observed 13C and 15N chemical shifts. Two methods were employed for calculation of equilibrium constants. The prototropic equilibria exhibited by the system studied are found to be controlled by enthalpy rather than entropy.

Intermolecular (OHO)- hydrogen bond formed by a hydroxyquinoline derivative

Wiench J. W., Stefaniak L., Grech E.

Bulletin of the Polish Academy of Sciences. Chemistry

1999

Vol. 47, No. 1

67-75

(1)H, (13)C, (14)N, (15)N, (17)0, and (19)F NMR data are presented for HTFMQ and its complexes with DMAN in 2 .land 1 : 1 molar ratios. GIAO-CHF molecular orbital calculations for the [1H] and [4H] forms of the free molecule and its anion are also performed. The results show that the [4H] form of HTFMQ predominates in acetonitrile solutions. In both complexes with DMAN, HTFMQ forms a semi-anion containing an intermolecular hydrogen bond.