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  • Title: Unconventional hydrogen bonding and π-stacking in two substituted pyridine carboxamides.
    Author: Wilson CR, Munro OQ.
    Journal: Acta Crystallogr C; 2010 Oct; 66(Pt 10):o513-6. PubMed ID: 20921618.
    Abstract:
    The crystal structures of two para-substituted aryl derivatives of pyridine-2-carboxamide, namely N-(4-fluorophenyl)pyridine-2-carboxamide, C(12)H(9)FN(2)O, (I), and N-(4-nitrophenyl)pyridine-2-carboxamide, C(12)H(9)N(3)O(3), (II), have been studied. Compound (I) exhibits unconventional aryl-carbonyl C-H...O and pyridine-fluorine C-H...F hydrogen bonding in two dimensions and well defined π-stacking involving pyridine rings in the third dimension. The conformation of (II) is more nearly planar than that of (I) and the intermolecular interactions comprise one-dimensional aryl-carbonyl C-H...O hydrogen bonds leading to a stepped or staircase-like progression of loosely π-stacked molecules. The close-packed layers of planar π-stacked molecules are related by inversion symmetry. Two alternating interplanar separations of 3.439 (1) and 3.476 (1) Å are observed in the crystal lattice and are consistent with a repetitive packing sequence, ABA'B'AB…, for the π-stacked inversion pairs of (II).
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