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Published on: October 10, 2013
An ab initio and cryospectroscopic study of the hydrogen chloride and boron trifluoride complexes of cyclopropene
Gert P Everaert1, Wouter A Herrebout, Benjamin J van der Veken
1Department of Chemistry, University of Antwerp, Groenenborgerlaan 171, B2020 Antwerp, Belgium.
Abstract:
Mid-infrared spectra of cyclopropene (c-C3H4) mixtures with HCl or BF3, dissolved in liquefied argon and in liquefied nitrogen have been examined. Evidence was found for the formation of two different isomers of the 1:1 complexes: a pi-type complex in which the interaction occurs with the pi-bond of cyclopropene, and a sigma-type complex in which the electron acceptors interact with one of the CC single bonds. At lower temperatures, indications for the formation of a 1:2 chain-type complex were found. Using spectra recorded between 90 and 124 K in liquid argon, the complexation enthalpies for the pi- and sigma-complexes with HCl were determined to be -8.8(3) and -7.9(3) kJ mol-1, respectively. For the pi-complex with BF3 a value of -7.4(3)kJ mol-1 was found. Structural and spectral information on the 1:1 complexes was obtained from B3LYP/6-311++G(d,p) and MP2(FC)/6-31+G(d) calculations. Using Free Energy Perturbation Monte Carlo simulations to calculate the solvent influences, and statistical thermodynamics to account for zero-point vibrational and thermal contributions, the solution enthalpies were transformed into complexation energies with values of -15.5(6) and -13.8(8) kJ mol-1 for the pi- and sigma-isomers of c-C3H4.HCl, respectively, and of -12.7(8) kJ mol-1 for the pi-type BF3 complex.
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