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Charge-Separated Reactive Intermediates from the UV Photodissociation of Chlorobenzene in Solution.

ABSTRACT: Although ultraviolet (UV)-induced photochemical cleavage of carbon-halogen bonds in gaseous halocarbons is mostly homolytic, the photolysis of chlorobenzene in solution has been proposed to produce a phenyl cation, c-C₆H₅⁺, which is a highly reactive intermediate of potential use in chemical synthesis and N₂ activation. Any evidence for such a route to phenyl cations is indirect, with uncertainty remaining about the possible mechanism. Here, ultrafast transient absorption spectroscopy of UV-excited (λ = 240 and 270 nm) chlorobenzene solutions in fluorinated (perfluorohexane) and protic (ethanol and 2,2,2-trifluoroethanol) solvents reveals a broad electronic absorption band centered at 540 nm that is assigned to an isomer of chlorobenzene with both charge-separated and triplet-spin carbene character. This spectroscopic feature is weaker, or absent, when experiments are conducted in cyclohexane. The intermediate isomer of chlorobenzene has a solvent-dependent lifetime of 30-110 ps, determined by reaction with the solvent or quenching to a lower-lying singlet state. Evidence is presented for dissociation to ortho-benzyne, but the intermediate could also be a precursor to phenyl cation formation.

SUBMITTER: Kao MH

PROVIDER: S-EPMC9549464 | biostudies-literature | 2022 Oct

REPOSITORIES: biostudies-literature

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Charge-Separated Reactive Intermediates from the UV Photodissociation of Chlorobenzene in Solution.

Kao Min-Hsien MH Orr-Ewing Andrew J AJ

The journal of physical chemistry. A 20220922 39

Although ultraviolet (UV)-induced photochemical cleavage of carbon-halogen bonds in gaseous halocarbons is mostly homolytic, the photolysis of chlorobenzene in solution has been proposed to produce a phenyl cation, c-C6H5+, which is a highly reactive intermediate of potential use in chemical synthesis and N2 activation. Any evidence for such a route to phenyl cations is indirect, with uncertainty remaining about the possible mechanism. Here, ultrafast ...[more]

PMID: 36148486

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Dataset Information

Charge-Separated Reactive Intermediates from the UV Photodissociation of Chlorobenzene in Solution.

Publications

Charge-Separated Reactive Intermediates from the UV Photodissociation of Chlorobenzene in Solution.

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