Infrared identification of the σ-complex of Cl-C6H 6 in the reaction of chlorine atom and benzene in solid para-hydrogen

Mohammed Bahou, Henryk Arnold Witek, Yuan-Pern Lee*

*Corresponding author for this work

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The reaction of a chlorine atom with benzene (C6H6) is important in organic chemistry, especially in site-selective chlorination reactions, but its product has been a subject of debate for five decades. Previous experimental and theoretical studies provide no concrete conclusion on whether the product is a π- or σ-form of the Cl-C6H 6 complex. We took advantage of the diminished cage effect of para-hydrogen (p-H2) to produce Cl in situ to react with C 6H6 (or C6D6) upon photolysis of a Cl2/C6H6 (or C6D6)/p- H2 matrix at 3.2 K. The infrared spectrum, showing intense lines at 1430.5, 833.6, 719.8, 617.0, and 577.4 cm-1, and several weaker ones for Cl-C6H6, and the deuterium shifts of observed new lines unambiguously indicate that the product is a 6-chlorocyclohexadienyl radical, i.e., the σ-complex of Cl-C6H6. Observation of the σ-complex rather than the π-complex indicates that the σ-complex is more stable in solid p-H2 at 3.2 K. The spectral information is crucial for further investigations of the Cl + C 6H6 reaction either in the gaseous or solution phase.

Original languageEnglish
Article number074310
JournalJournal of Chemical Physics
Issue number7
StatePublished - 21 Feb 2013

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