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Geometry of alfa-Diaryl Type CH-NH Acids of Pharmacological Interest. Crystal Structures of alfa-(4-Chlorophenyl)- and alfa-(2,4-Dichlorophenyl-alfa-2-pyrazilideneacetonitrilles

Główka M., Olczak A., Bojarska J., Szczesio M., Kozłowska K., Foks H.

Polish Journal of Chemistry

2005

Vol. 79 / nr 8

1275-1284

alfa-Diarylacetonitriles represent a very interesting model for studying the structure-activity relationship, due to restricted freedom of conformational diversity and, on the other hand, a very wide range of biological activities, including analgesic, non-narcotic antiinflammatory and antirheumatic. The two studied representatives have in the crystal state very uniform molecular structures, which may be characterized by a dihedral angle between the two aromatic rings, being 77 graduate in 4-chlorophenyl; 74 graduate and 80 graduate in 2,4-dichlorophenyl derivative, respectively. Despite the presence of groups capable of weak C-H hydrogen bonds formation there is only one short C-H...X contact (X = N in 4 position of the pyrazinyl ring) of 2.40 ?, being significantly shorter than the sum of van der Waals radii of respective atoms. The contact found in the 2,4-dichlorophenyl derivative crystal is in accord with CH-NH proton transfer observed in these compounds.

Crystal and molecular structures of 1,1-bis(methylthio)-4-(2-pyridyl)-2,3,5-triaza-1,3-pentadiene and its 5-phenyl derivative

Główka M., Martynowski D., Olczak A., Kozłowska K., Ołubek Z., Orlewska C., Foks H.

Polish Journal of Chemistry

1999

vol. 73 nr 5

845-851

Structures of the two dimethylthiomethylene-2-pyridinecarboxamide hydrazones have been examined spectroscopially and by X-ray diffraction to establish the dominant tautometric form and conformation. The two crystal structures are very similar with approximately planar conformation and intramolecular hydrogen bond between 4-imine group as hydrogen donor and pyridyl N atom as an acceptor. Several significant differences found may be easily explained by phenyl substitution in one of the compounds. The benzene ring in compound 2 is twisted by about 40o in relation to the mean molecular plane due to packing forces. An interesting feature of the structures is the deviation of the pyridyl ring by 11-14o from the mean 2,3,5-triaza-1,3-pentadiene plane in the two structures, despite the intramolecular hydrogen bond spanning the two fragments. It agrees with the elongation of C(4)-pyridine bond to 1.488 A, which corresponds with the lack of conjugation between p electrons of the pyridine ring and a lone pair at adjacent N(4) atom.