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Effect of benzoannulation on tautomeric preferences of 4,6-di(pyridin-2-yl)cyclohexane-1,3-dione.

ABSTRACT: Density functional theory (DFT) calculations at the B3LYP/6-311+G(d,p) level show that 4,6-di(pyridin-2-yl)cyclohexane-1,3-dione is a labile compound. On the other hand, its dienolimine tautomer (4,6-di(pyridin-2-yl)cyclohaxa-1,3-diene-1,3-diol) seems stable enough to be present in vacuum. Alternatively the equilibriated species are (i) dienolimine and enolimine-enaminone ((6Z)-3-hydroxy-6-(pyridin-2(1H)-ylidene)-4-(pyridine-2-yl)cyclohex-3-enone) or (ii) dienolimine, enolimine-enaminone and dienaminone ((4Z,6Z)-4,6-di(pyridin-2(1H)-ylidene)cyclohexane-1,3-dione). Benzoannulation of the pyridine ring at position 5,6 was found to increase the contribution of the tautomers which contain the enaminone moiety. Energies of the transition states between the stable tautomers were also calculated in order to estimate activation energy of the proton transfer. Values of the geometry based harmonic oscillator model of aromaticity (HOMA) index and Laplacian of the electron density in the hydrogen bond critical point (based on quantum theory of atom in molecules) shows that the enaminone moiety in the tautomers studied are stabilized by stronger intramolecular hydrogen bond than this present in the enolimine moiety.

SUBMITTER: Dobosz R

PROVIDER: S-EPMC3713269 | biostudies-literature |

REPOSITORIES: biostudies-literature

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2,2-Dimethyl-5-[(pyridin-2-yl-amino)-methyl-idene]-1,3-dioxane-4,6-dione.

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Crystal structure, Hirshfeld surface analysis and spectroscopic characterization of the di-enol tautomeric form of the compound 3,3'-[(2-sulf-an-yl-idene-1,3-di-thiole-4,5-di-yl)bis-(sulfane-di-yl)]bis-(pentane-2,4-dione).

Project description:The reaction between [TBA]2[Zn(dmit)2] and 3-chloro-2,4-penta-nedione yielded single crystals of the title compound, (3E,3'E)-3,3'-[(2-sulfanylidene-1,3-dithiole-4,5-diyl)bis(sulfanediyl)]bis(4-hydroxypent-3-en-2-one), C13H14O4S5, after solvent evaporation. The title compound crystallizes in the triclinic space group P with two mol-ecules related by an inversion center present in the unit cell. The central thione ring moiety contains a carbon-carbon double bond covalently linked to two sulfoxide substituents located outside of the plane of the ring. The S-C-C-S torsion angles are -176.18 (8) and -0.54 (18)°. Intra-molecular hydrogen bonds occur within the two dione substituents (1.67-1.69 Å). Adjacent asymmetric units are linked by C-H⋯S (2.89-2.90 Å), S⋯S [3.569 (1) Å] and O⋯H [2.56-2.66 Å between non-stacked thione rings] short contacts.

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Crystal structures and Hirshfeld surface analyses of 2-[(4,6-di-amino-pyrimidin-2-yl)sulfan-yl]-N-(pyridin-2-yl)acetamide and 2-[(4,6-di-amino-pyrimidin-2-yl)sulfan-yl]-N-(pyrazin-2-yl)acetamide.

Project description:In the title compounds, C11H12N6OS (I) and C10H11N7OS (II), the di-amino-pyrimidine ring makes dihedral angles of 71.10?(9)° with the pyridine ring in (I) and 62.93?(15)° with the pyrazine ring in (II). The ethanamine group, -CH2-C(=O)-NH- lies in the plane of the pyridine and pyrazine rings in compounds (I) and (II), respectively. In both compounds, there is an intra-molecular N-H?N hydrogen bond forming an S(7) ring motif and a short C-H?O inter-action forming an S(6) loop. In the crystals of both compounds, mol-ecules are linked by pairs of N-H?N hydrogen bonds, forming inversion dimers with R22(8) ring motifs. In (I), the dimers are linked by N-H?O and N-H?N hydrogen bonds, forming layers parallel to (1[Formula: see text] [Formula: see text]). The layers are linked by offset ?-? inter-actions [inter-centroid distance = 3.777?(1)?Å], forming a three-dimensional supra-molecular structure. In (II), the dimers are linked by N-H?O, N-H?N and C-H?O hydrogen bonds, also forming a three-dimensional supra-molecular structure.

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