Bulletin of the Korean Chemical Society

Korean Chemical Society (대한화학회)
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Product-Resolved Photodissociations of Iodotoluene Radical Cations

  • Shin, Seung-Koo (FT-ICR Laboratory, Department of Chemistry, Pohang University of Science and Technology) ;
  • Kim, Byung-Joo (Division of Chemistry and Radiation, Korea Research Institute of Standards and Science) ;
  • Jarek, Russell L. (Department of Chemistry, University of California) ;
  • Han, Seung-Jin (Department of Chemistry, University of California)
  • Published : 2002.02.20
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Abstract

Photodissociations of o-, m-, and p-iodotoluene radical cations were investigated by using Fourier-transform ion cyclotron resonance (FT-ICR) spectrometry. Iodotoluene radical cations were prepared in an ICR cell by a photoionization charge-transfer method. The time-resolved one-photon dissociation spectra were obtained at 532 nm and the identities of $C_7H_7^+$ products were determined by examining their bimolecular reactivities toward toluene-$d_8$. The two-photon dissociation spectra were also recorded in the wavelength range 615-670 nm. The laser power dependence, the temporal variation, and the identities of $C_7H_7^+$ were examined at 640 nm. The mechanism of unimolecular dissociation of iodotoluene radical cations is elucidated: the lowest barrier rearrangement channel leads exclusively to the formation of the benzyl cation, whereas the direct C-I cleavage channel yields the tolyl cations that rearrange to both benzyl and tropylium cations with dissimilar branching ratios among o-, m-, and p-isomers. With a two-photon energy of 3.87 eV at 640 nm, the direct C-I cleavage channel results in the product branching ratio, [tropylium cation]/[benzyl cation], in descending order, 0.16 for meta >0.09 for ortho >0.05 for para.

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