Diagnostic fragmentations of adducts formed between carbanions and carbon disulfide in the gas phase. A joint experimental and theoretical study

Abstract

Selected carbanions react with carbon disulfide in a modified LCQ ion trap mass spectrometer to form adducts, which when collisionally activated, decompose by processes which in some cases identify the structures of the original carbanions. For example (i) C₆H₅⁻ + CS₂→ C₆H₅CS₂⁻→ C₆H₅S⁻ + CS, occurs through a 3-membered ring ipso transition state, and (ii) the reaction between C₆H₅CH₂⁻ and CS₂ gives an adduct which loses H₂S, whereas the adduct(s) formed between o-CH₃C₆H₅⁻ and CS₂ loses H₂S and CS. Finally, it is shown that decarboxylation of C₆H₅CH₂CH₂CO₂⁻ produces the β-phenylethyl anion (PhCH₂CH₂⁻), and that this thermalized anion reacts with CS₂ to form C₆H₅CH₂CH₂CS₂⁻ which when energized fragments specifically by the process C₆H₅CH₂CH₂CS₂⁻→ C₆H₅CH₂⁻CHC(S)SH → [(C₆H₅CH₂CHCS) ⁻SH] → C₆H₅CH₂CCS⁻ + H₂S. Experimental findings of processes (ii) and (iii) were aided by deuterium labelling studies, and all reaction profiles were studied by theoretical calculations at the UCCSD(T)/6-31+G(d,p)//B3LYP/6-31+G(d,p) level of theory unless indicated to the contrary.