Stabilization of Vinyl Cations by β-Silicon: A Quantitative Mass Spectrometric Study

The stabilization afforded a vinyl cation by a β-(CH3)3Si substituent has been determined by measuring in a high-pressure mass spectrometer the thermodynamic data for the association of three alkynes (RCCR‘) with (CH3)3Si+ and with the proton. The measured −ΔH° (kcal mol-1) and −ΔS° (in parentheses, cal K-1 mol-1) values for the reaction (CH3)3Si+ + RCCR‘ ⇄ (CH3)3Si·C(R)CR‘+ are as follows: 1-hexyne (R = H, R‘ = n-C4H9) 25.9 ± 1.5 (19.1 ± 0.2), …