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An electronic structure theory investigation of the physical chemistry of the intermolecular complexes of cyclopropenylidene with hydrogen halides
Authors:Pradeep R Varadwaj  Arpita Varadwaj  Gilles H Peslherbe
Institution:1. Centre for Research in Molecular Modeling, Department of Chemistry & Biochemistry, Concordia University, 7141 Sherbrooke Street West, Montréal, Québec H4B 1R6, Canada Fax: (+1) 514 848 2868Fax: (+1) 514 848 2868;2. Centre for Research in Molecular Modeling, Department of Chemistry & Biochemistry, Concordia University, 7141 Sherbrooke Street West, Montréal, Québec H4B 1R6, Canada Fax: (+1) 514 848 2868
Abstract:The proton accepting and donating abilities of cyclopropenylidene (c‐C3H2) on its complexation with hydrogen halides H? X (X = F, Cl, Br) are analyzed using density‐functional theory with three functionals (PBE0, B3LYP, and B3LYP‐D) and benchmarked against second‐order Møller–Plesset (MP2) theory. Standard signatures including, inter alia, dipole moment enhancement, charge transfer from the carbenic lone pair to the antibonding σ*(H? X) orbital, and H? X bond elongation are examined to ascertain the presence of hydrogen bonding in these complexes. The latter property is found to be accompanied with a pronounced red shift in the bond stretching frequency and with a substantial increase in the infrared intensity of the band on complex formation. The MP2/aug‐cc‐pVTZ c‐C3H2···H? F complex potential energy surface turns out to be an asymmetric deep single well, while asymmetric double wells are found for the c‐C3H2···H? Cl and c‐C3H2···H? Br complexes, with an energy barrier of 4.1 kcal mol?1 for proton transfer along the hydrogen bond in the latter complex. Hydrogen‐bond energy decomposition, with the reduced variational space self‐consistent field approach, indicates that there are large polarization and charge‐transfer interactions between the interacting partners in c‐C3H2···H? Br compared to the other two complexes. The C···H bonds are found to be predominantly ionic with partial covalent character, unveiled by the quantum theory of atoms in molecules. The present results reveal that the c‐C3H2 carbene divalent carbon can act as a proton acceptor and is responsible for the formation of hydrogen bonds in the complexes investigated. © 2012 Wiley Periodicals, Inc.
Keywords:cyclopropenylidene hydrogen halide complexes  hydrogen bonding  proton transfer  potential energy surface  electronic  vibrational and topological properties  electronic structure calculations
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