Synthesis and electron spin resonance spectroscopy of organo-sulfur radical cations
A series of new radical cations in 1,4-dithiin, 1,4-benzodithiin, 2,3-dihydro-1,4-dithiin, 1,4-dithiepin, 1,2-dithietane, 1,2-dithiolane, 1,2-dithiane series were prepared. The SOMO of 1,4-dithiin, 1,4-benzodithiin, 2,3-dihydro-1,4-dithiin radical cations were found to be symmetrical while the SOMO of cyclic 1,2-disulfide radical cations were found to be antisymmetrical. 2,3-Dihydro-1,4-dithiin, 1,4-dithiepin radical cations were found to have conformational preference at low temperature and the activation parameters for the ring inversion processes were obtained. For 1,2-bis(isopropylthio)cyclohexene radical cation, the unusually low value of (DELTA)H('(NOT=)) for the cyclohexene ring inversion was explained by secondary interactions between the isopropyl groups and the (alpha) methylene groups. Sulfur-centered radical cations were found to be capable of showing sizable long range couplings in the radical cations of 2,5-dithiabicyclo 4.2.1 non-3-ene, 2,3-dithiabicyclo 2.2.1 heptane, 2,3-dithiabicyclo 2.2.2 octane. It is established from all the ESR results that the hfs of a hydrogen (beta) to a sulfur atom with spin density arises predominantly from angle-dependent hyperconjugation. For disulfide radical cations (not including 1,2-dithietane radical cations), a value of 35 G was calculated for the constant B which is a measure of the magnitude of this interaction. For 1,2-dithietane radical cations, a (sigma)-delocalized electronic structure for the 3-electron bond is proposed to explain the unusual conformational preference and the unusually low values of a('H);Sulfur-centered radical cations were generated by oxidative rearrangement. Thus, 2,2-dialkyl-1,3-dithiolanes rearranged to form 2,3-dihydro-1,4-dithiin radical cations when treated with either H(,2)SO(,4) or Al(,2)Cl(,6)/CH(,2)Cl(,2). Similarly, 2,3-dialkyl-1,3-benzodithioles rearranged to form the 1,4-benzodithiin radical cations. Diaryl disulfides underwent oxidative rearrangement to form benzodithiete and thianthrene radical cations. Methylbenzyl disulfides underwent oxidative rearrangement to form polymethylbenzodithiete and 2,6-dimethylanthrancene radical cations.