25012-81-1Relevant articles and documents
Bond strengths of ethylene and acetylene
Ervin, Kent M.,Gronert, Scott,Barlow,Gilles, Mary K.,Harrison, Alex G.,Bierbaum, Veronica M.,DePuy, Charles H.,Lineberger,Ellison, G. Barney
, p. 5750 - 5759 (2007/10/02)
Negative ion photoelectron spectroscopy and gas-phase proton transfer kinetics were employed to determine the CH bond dissociation energies of acetylene, ethylene, and vinyl radical: D0(HCC-H) = 131.3 ± 0.7 kcal mol-1, D0(CH2CH-H) = 109.7 ± 0.8 kcal mol-1, and D0(CH2C-H) = 81.0 ± 3.5 kcal mol-1. The strengths of each of the other CH and CC bonds in acetylene and ethylene and their fragments were derived. The energy required to isomerize acetylene to vinylidene was also determined: HC≡CH → H2C=C: ΔHisom,0 = 47.4 ± 4.0 kcal mol-1. As part of this study, proton transfer kinetics in a flowing afterglow/selected-ion flow tube apparatus were used to refine the acidities of ethylene, acetylene, and vinyl. The gas-phase acidity of acetylene was tied to the precisely known values for hydrogen fluoride, ΔGacid,298(HF) = 365.6 ± 0.2 kcal mol-1, and water, ΔGacid,298(H2O) = 383.9 ± 0.3 kcal mol-1, yielding ΔGacid,298(HCC-H) = 369.8 ± 0.6 kcal mol-1. The gas-phase acidity equilibria of acetylene with isopropyl alcohol and tert-butyl alcohol were also measured. Combined with relative acidities from the literature, these measurements yielded improved acidities for the alcohols, ΔGacid,298((CH3)2CHO-H) = 370.1 ± 0.6 kcal mol-1, ΔGacid,298((CH3)3CO-H) = 369.3 ± 0.6 kcal mol-1, ΔGacid,298(C2H5O-H) = 372.0 ± 0.6 kcal mol-1, and ΔGacid,298(CH3O-H) = 375.1 ± 0.6 kcal mol-1. The gas-phase acidity of ethylene was measured relative to ammonia, ΔGacid,298(NH3) = 396.5 ± 0.4 kcal mol-1, giving ΔGacid,298(C2H4) = 401.0 ± 0.5 kcal mol-1. The gas-phase acidity of vinyl radical was bracketed, 375.1 ± 0.6 kcal mol-1 ≤ ΔGacid,298(CH2C-H) ≤ 380.4 ± 0.3 kcal mol-1. The electron affinities of ethynyl, vinyl, and vinylidene radicals were determined by photoelectron spectroscopy: EA(HCC) = 2.969 ± 0.010 eV, EA(CH2CH) = 0.667 ± 0.024 eV, and EA(CH2C) = 0.490 ± 0.006 eV.
