Intramolecular Electron Transfer in Heterosubstituted Benzene Derivatives as Probed by Dissociative Electron Attachment

Abstract

The electron transmission and dissociative electron attachment spectra of the 1-chloroalkyl benzene derivatives, C(6)H(5)(CH(2))(3)Cl and C(6)H(5)(CH(2))(4)Cl, and of the sulfur and silicon derivatives, C(6)H(5)SCH(2)Cl, C(6)H(5)Si(CH(3))(2)CH(2)Cl and C(6)H(5)CH(2)Si(CH(3))(2)CH(2)Cl, are presented for the first time. The relative Cl(-) fragment anion currents generated by electron attachment to the benzene pi* LUMO are measured in the series C(6)H(5)(CH(2))(n)Cl, with n = 1-4, and in the heteroatomic compounds. The Cl(-) yield reflects the rate of intramolecular electron transfer between the pi-system and the remote chlorine atom, which in turn depends on the extent of through-bond coupling between the localized pi* and sigma*(Cl-C) orbitals. In compounds C(6)H(5)(CH(2))(n)Cl the Cl(-) current rapidly decreases with increasing length of the saturated chain. This decrease is significantly attenuated when a carbon atom of the alkyl skeleton is replaced with a third-row heteroatom. This greater ability to promote through-bond coupling between the pi* and sigma*(Cl-C) orbitals is attributed to the sizably lower energy of the empty sigma*(S-C) and sigma*(Si-C) orbitals with respect to the sigma*(C-C) orbitals. In the sulfur derivative the increase of the Cl(-) current is larger than in the silicon analogue. In this case, however, other negative fragments are observed, due to dissociation of the S-C bonds.

Dissociative electron attachment in nonplanar chlorocarbons with π∗/σ∗-coupled molecular orbitals

“…The conformer energies differ somewhat from those of Modelli et al 7 who used DFT/B3LYP calculations with the same basis set. The conformer energies differ somewhat from those of Modelli et al 7 who used DFT/B3LYP calculations with the same basis set.…”

“…The VAEs of the C 6 H 5 -͑CH 2 ͒ n -Cl compounds have been determined using ETS for n = 1 ͑benzyl chloride͒ by Stricklett et al 16 and Distefano et al, 23 and for n=2-4 by Modelli and co-workers, 6,7 and in the present work. As in the chloroethenes, the ‫ء‬ resonances are very prominent, and there is some concern that the VAEs associated with the C-Cl ‫ء‬ resonances could be distorted by their proximity.…”

“…Modelli et al 7 have noted earlier that the peak yields of Cl − are higher in the phenyl derivatives than in the ethylenic compounds at each size of spacer unit. For the record, we find ratios of 1.4, 6.4, 4.8, and 1.8 for n=1-4 respectively in this comparison.…”

“…Unfortunately, Fig. Readers are referred to Refs 6,7,16, and 23 for the ET spectra. We will again cite these estimated values for ‫ء‬ VAEs but note that in the phenylchloroalkanes these values may be lower bounds.…”

Phenol, chlorobenzene and chlorophenol isomers: resonant states and dissociative electron attachment

“…On the other hand, the DEA experiments indicate dissociative processes in the peripheral bonds, i.e., not in the benzene skeleton but in the benzene ring substituents. This apparent contradiction is explained in terms of dissociative intramolecular electron transfer 14–17…”