A new polymorph of N,N'-bis-(2,6-diisopropyl-phen-yl)formamidine, C(25)H(36)N(2), is reported, which is different from the previously reported ortho-rhom-bic structure. The mol-ecule crystallizes in the E-anti configuration, with tautomeric disorder of the N-bonded H atoms and no clear distinction between imine and amine functionalities. The mol-ecules form hydrogen-bonded dimers with inter-mol...

The mol-ecule of the title compound, C(15)H(15)NO(2), adopts the enol-imine tautomeric form and has a strong intra-molecular O-H⋯N hydrogen bond as a result. The mol-ecule is almost planar, with a maximum deviation of 0.1038 (15) Å for the meth-oxy C atom. A weak C-H⋯π inter-action and a weak C-H⋯O hydrogen bond are present in the crystal.

In this paper we seek to determine the shape of the barrier between the normal and tautomeric conformers for some excited singlet and triplet states in the molecules of guanine and cytosine. The molecules as considered isolated and a particular movement of the H atom is analysed. The semi-empirical CNDO/2-CI has been used. The calculated results are compared with the available experimental data.

The title Schiff base, C23H27ClN2O adopts the phenol-imine tautomeric form, with an intra-molecular O-H⋯N hydrogen bond, which generates an S(6) ring motif. Three C atoms of the heterocyclic moiety of the hexa-hydro-pyrido-quinoline unit, as well as the two methyl groups bonded to one of these C atoms, are disordered over two set of sites, with anoccupancy ratio of 0.740 (4):0.260 (4).

The title compound, C(15)H(11)Cl(2)NO(2), is a Schiff base which adopts the phenol-imine tautomeric form in the solid state, being stabilized by a strong intra-molecular O-H⋯N hydrogen bond. The mol-ecule is almost planar (r.m.s. deviation for all non-H atoms = 0.049 Å), displaying a dihedral angle of 3.1 (3)° between the planes of the two aromatic rings.

A review of selected literature data related to intramolecular hydrogen bonding in ortho-hydroxyaryl Schiff bases, ortho-hydroxyaryl ketones, ortho-hydroxyaryl amides, proton sponges and ortho-hydroxyaryl Mannich bases is presented. The paper reports on the application of experimental spectroscopic measurements (IR and NMR) and quantum-mechanical calculations for investigations of the proton tr...

The title compound, C(20)H(19)N(3)O, exists in a keto-enamine tautomeric form. The pyrazolone ring makes dihedral angles of 20.52 (10) and 77.73 (5)° with the two phenyl rings and an intra-molecular N-H⋯O hydrogen bond occurs. A weak inter-molecular C-H⋯O hydrogen bond is observed in the crystal structure. The allyl group is disordered over two positions, with site-occupancy factors of 0.533 (5...

The title compound, C28H33N2S2P, adopts the thione tautomeric form, as supported by the C-S distance [1.6744 (18) Å]. The Schiff base exhibits an E conformation about the C=N bond but a Z conformation about the C-N bond. The terminal chain is disordered over two sets of sites with an occupancy ratio of 0.732 (3):0.268 (3). In the crystal, pairs of N-N-H hydrogen bonds between the thione groups ...

Four new crystalline forms of piroxicam have been obtained and studied by single-crystal X-ray structure analysis. These comprise an addition salt with hydrochloric acid, acetic and isobutyric acids solvates, as well as piroxicam and furosemide cocrystal acetone solvate. All these new structures contribute to the variety of already known piroxicam crystalline forms. The analysis of conformation...

In this work we propose the synthesis of thiazolidine and bisthiazolidine derivatives, and the structure of these compounds were studied using elemental analysis, IR, H-NMR and C-NMR spectroscopy. Tautomeric properties and conformations were investigated by semi-empirical AM1, MNDO and PM3, and ab initio calculations to illustrate the conformational analysis. All calculations lead to the same r...