Thermal stability of intermediate sized acetylenic compounds and the heats of formation of propargyl radicals

Abstract 4‐Methylhexyne‐1, 5‐methylhexyne‐1, hexyne‐1, and 6‐methylheptyne‐2 have been decomposed in comparative‐rate single‐pulse shock‐tube experiments. Rate expressions for the initial decomposition reactions at 1100°K and from 2 to 6 atm pressure are In combination with previous results, rate expressions for propargyl CC bond cleavage are related to that for the alkanes by the expression These results yield a propargyl resonance energy of D(nC3H7‐H) – D(C3H3‐H) = 36 ± 2 kJ, in excellent agreement with a previous shock‐tube study. They also lead to D(CH3C≡CCH2‐H) – D(C3H3‐H) = 0.6 ± 3 kJ, D(sC4H9‐H) – D(iC3H7‐H) = 0 ± 3 kJ, D(iC4H9‐H) – D(nC3H7‐H) = 2 ± 3 kJ, and D(nC3H7‐H) – D(iC3H7‐H) = 13.9 ± 3 kJ (all values are for 300°K). The systematics of the molecular decomposition process are explored.