Gas phase generation of HCCCS and CCCHS radicals from anionic precursors. The rearrangement of CCCHS to HCCCS. A joint experimental and theoretical study

Abstract

Theoretical studies at the CCSD(T)/aug-cc-pVDZ//B3LYP/aug-cc-pVDZ level of theory indicate that there are four stable radicals with CCC bond connectivity on the C3HS potential surface, namely, HCCCS, CCHCS, CCCHS, and (cyclo-C3H)=S. Of these structures, two have been synthesized by one electron vertical oxidation of precursor anions, formed as follows: (i) CH3-C≡C-S-C2H5 + O-· → (HCCCS)- + H2O + C2H5· and (ii) Me3Si-C≡C-CH(cyclo-SCH2CH2S) + F- → -C≡C-CH=S + Me3SiF + cyclo-SC2H4. A comparison of the -CR+ and -NR+ spectra of these two anions indicate that the neutral HCCCS is stable with a lifetime of at least 1 μs, whereas the oxidation of (CCCHS)- leads to two neutrals, CCCHS and HCCCS. Theoretical calculations indicate that the rearrangement of CCCHS to HCCCS can occur by three pathways; concerted H or S rearrangements or the stepwise H rearrangement process CCCCHS → CCHCS → (cyclo-C3H)=S → HCCCS. Comparison of the -CR+ and -NR+ spectra of (CC13CHS)- indicates that at least a part of the rearrangement involves the S migration pathway. Theoretical considerations suggest that H rearrangement should compete with S rearrangement: there is no experimental evidence to confirm or refute this proposal.