The synthesis and structural characterization of 2-(furan-2-yl)-1-(furan-2-ylmethyl)-1H-benzimidazole, 1; its hydrochloride monohydrate salt, 2; and the hydrobromide salt of 5,6-dimethyl-2-(furan-2-yl)-1-(furan-2-ylmethyl)-1H-benzimidazole, 3, are described. 1 displays two sets of aromatic interactions, each of which involves pairs of molecules in a head-to-tail arrangement. Interaction 1a exhibits both intermolecular C-H/π interactions between the 2-(furan-2-yl), Fn, and the 1-(furan-2-ylmethyl), MeFn, substituents and π/π interactions involving the Fn substituents between inversion-center related molecules. Interaction 1b involves π/π interactions involving both the benzene ring, Bz, and the imidazole ring, Im, of the benzimidazole. The net result is the formation of chains of molecules along the c-axis. 2 exhibits N-H…OH2…Cl hydrogen bonding that result in chains of molecules parallel to the a-axis. There is also a head-to-head aromatic stacking of the protonated benzimidazole cations in which the Bz and Im rings of one molecule interact with the Im and Fn rings of adjacent molecules in the chain. 3 displays N-H…Br hydrogen bonding and π/π interactions involving inversion center-related benzimidazole rings in a head-to-tail arrangement. All four of the π/π interactions observed involve slippage of the molecules along the major molecular axis. In 1a, 1b, and 2, the molecules are also slipped along the minor molecular axis. BSSE-corrected (counterpoise method) interaction energies were calculated for each interaction [DFT, M06-2X/6-31+G(d)] employing atomic coordinates obtained in the crystallographic analyses. For Ia, the analysis was used to partition the interaction energies into C-H/π and the π/π components. Energy-minimized structures were used to determine the optimal interplanar spacing, slip distance along the major molecular axis and slip distance along the minor molecular axis for 2-(furan-2-yl)-1H-benzimidazole. The results of the crystallographic analysis and interaction energy calculations will be presented.

Crystallographic characterization of three furan-substituted benzimidazoles and calculation of C-H/π and π/π interaction energies

249th National Meeting (2015)

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