16331-65-0Relevant articles and documents
The Ever-surprising chemistry of boron: Enhanced acidity of phosphine·boranes
Hurtado, Marcela,Yanez, Manuel,Herrero, Rebeca,Guerrero, Andres,Juan Z. Davalos,Jose-Luis, M. Abboud,Khater, Brahim,Guillemin, Jean-Claude
supporting information; experimental part, p. 4622 - 4629 (2009/12/29)
The gas-phase acidity of a series of phosphines and their corresponding phosphine·borane derivatives was measured by FT-ICR techniques. BH 3 attachment leads to a substantial increase of the intrinsic acidity of the system (from 80 to 110 kJ mol-1). This acidity-enhancing effect of BH3 is enormous, between 13 and 18 orders of magnitude in terms of ionization constants. This indicates that the enhancement of the acidity of protic acids by Lewis acids usually observed in solution also occurs in the gas phase. High- level DFT calculations reveal that this acidity enhancement is essentially due to stronger stabilization of the anion with respect to the neutral species on BH3 association, due to a stronger electron donor ability of P in the anion and better dispersion of the negative charge in the system when the BH3 group is present. Our study also shows that deprotonation of ClCH2PH2 and ClCH 2PH2·BH3 is followed by chloride departure. For the latter compound deprotonation at the BH3 group is found to be more favorable than PH2 deprotonation, and the subsequent loss of Cl- is kinetically favored with respect to loss of Cl - in a typical SN2 process. Hence, ClCH2PH 2·BH3 is the only phosphine·borane adduct included in this study which behaves as a boron acid rather than as a phosphorus acid.
Gas-phase ionic reactions of benzyl and methoxide anions
Gatev, Geo G.,Zhong, Meili,Brauman, John I.
, p. 531 - 536 (2007/10/03)
Gas-phase reactions of benzyl and methoxide anions with alkyl formate and other esters were compared using Fourier transform io cyclotron resonance spectroscopy. Although these anions have similar basicities, in many cases the reaction pathways differ.
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.
