The population analysis of the hydrogen bond atoms was analyzed within the different basis sets for model molecular systems for the ground and low-lying excited electronic states. The Mulliken, Lőwdin and Hirshfeld methods were used in our investigations. It has been shown that normally the proton is transferred, however, in some excited electronic states the hydrogen atom displacement might be...

The title compound, C(14)H(12)ClNO, a Schiff base derived from 3-methyl-salicyl-aldehyde, crystallizes in the phenol-imine tautomeric form with an E conformation for the imine functionality. The mol-ecule is not planar, the dihedral angle between the aromatic rings being 36.38 (5)°. The hy-droxy H atom is involved in a strong intra-molecular O-H⋯N hydrogen bond, generating an S(6) ring.

The title Schiff base, C(19)H(24)N(2)O(3), exists in the crystal structure in the phenol-imine tautomeric form with an intra-molecular O-H⋯N hydrogen bond. The planes of the aromatic rings form a dihedral angle of 36.8 (8)°. The crystal packing is characterized by C-H⋯O hydrogen bonds and π-π stacking inter-actions [centroid-centroid distance = 3.478 (4)Å].

There are two independent mol-ecules in the asymmetric unit of the title compound, C(15)H(14)BrNO(3), with very similar geometrical parameters. Each mol-ecule adopts the phenol-imine tautomeric form, with strong intra-molecular O-H⋯N hydrogen bonds. The two mol-ecules are non-planar, the dihedral angles between the two aromatic rings being are 24.6 (2) and 30.30 (13)°.

The title mol-ecule, C(20)H(21)NO(6), adopts a keto-amine tautomeric form. An intra-molecular N-H⋯O hydrogen bond, classified as a resonanse-assisted hydrogen bond, influences the mol-ecular conformation; the two benzene rings form a dihedral angle of 24.6 (1)°. In the crystal structure, weak inter-molecular C-H⋯O hydrogen bonds link mol-ecules into chains propagating along [001].

ab initio and dft methods have been used to study the seven tautomeric forms of 5-methylcytosine molecule.the related tautomer in gas phase have been studied at hf/6-31g, hf/6-31g* and b3lyp/6-31g* levels oftheory. the structures,enthalpies,entropies,gibbs free energies,relative tautomerization energies of tautomersand tautomeric equilibrium constants were compared and analyzed along with full ...

In the title salt, NH(4) (+)·C(4)H(3)N(2)O(2)S(-), the asymmetric unit comprises two half-occupied ammonium positions and a 4,6-dioxo-2-sulfanylidene-1,3-diazinan-5-ide anion. The anion shows C(2) as well as C(s) symmetry and is present in its diketonic tautomeric form. Intra-cyclic angles span a range from 116.64 (9)-124.67 (9)°. Inter-molecular N-H⋯O hydrogen bonds connect the cations and ani...