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Matrix Infrared Spectra and Density Functional Calculations for New iso-Halomethanes: CHCl2–Cl, CHFCl–Cl, CFCl2–Cl, CHBr2–Br, and CBr3–Br in Solid Argon

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journal contribution
posted on 01.08.2013 by Han-Gook Cho, Lester Andrews
Laser ablation of transition metals for reactions with halocarbons to produce new metal bearing molecules also exposed these samples to laser plume radiation and its resulting photochemistry. Investigations with CCl4 also produced several known neutral and charged intermediate species, including the iso-tetrachloromethane CCl3–Cl observed in previous work and identified by the Maier group. CHCl2–Cl, CHFCl–Cl, and CFCl2–Cl, photoisomers of CHCl3, CHFCl2, and CFCl3, were also identified in matrix IR spectra. The new C–X bonds are shorter than those of the reactants, and the Cl atom that is weakly bonded to the residual Cl atom forms an unusually strong C–Cl bond. NBO analysis reveals substantial CCl double-bond character, and the weak Cl···Cl bond is largely ionic. Therefore, the CHX2–X species can be represented as HXCXδ+···Xδ−. Ionic properties are revealed for CCl3–Cl, which has an average C–Cl bond length near the median for the CCl3 radical and cation and a natural charge of +0.49 for the CCl3 subunit. IRC computations reproduce smooth interconversion between the reactants and products, and the transition state is energetically close to the product, which is consistent with its disappearance on visible irradiation.