31139-07-8Relevant academic research and scientific papers
Experimental studies of allene, methylacetylene, and the propargyl radical: Bond dissociation energies, gas-phase acidities, and ion-molecule chemistry
Robinson, Marin S.,Polak, Mark L.,Bierbaum, Veronica M.,DePuy, Charles H.,Lineberger
, p. 6766 - 6778 (1995)
Electron affinities and ΔHacid are combined in a thermochemical cycle to arrive at bond dissociation energies for allene, methylacetylene, and the propargyl radical: D0(CH2=C=CH-H) = 88.7 ± 3 kcal mol-1, D0(H-CH2C≡CH) = 90.3 ± 3 kcal mol-1, D0(CH3C≡C-H) = 130.2 ± 3 kcal mol-1, and D0(CH2=C=C-H) = 100 ± 5 kcal mol-1. Electron affinity measurements were determined using negative ion photoelectron spectroscopy and yielded the following for the propargyl, 1-propynyl, and propadienylidene radicals: EA(CH2=C=CH) = 0.918 ± 0.008 eV, EA(CH3C≡C) = 2.718 ± 0.008 eV, and EA(CH2=C=C?) = 1.794 ± 0.008 eV. Gas-phase acidity measurements were made using proton transfer kinetics in a flowing afterglow/selected-ion flow tube and yielded the following for allene, methylacetylene, and the propargyl radical: ΔGacid(CH2=C=CH-H) = 372.8 ± 3 kcal mol-1, ΔGacid(H-CH2C=CH) = 374.7 ± 3 kcal mol-1, ΔGacid(CH3C≡C-H) = 373.4 ± 2 kcal mol-1, and ΔGacid(CH2=C=CH) = 364 ± 5 kcal mol-1. ΔGacid was converted to ΔHacid by employing ΔSacid: ΔHacid(CH2=C=CH-H) = 381.1 ± 3 kcal mol-1, ΔHacid(H-CH2C≡CH) = 382.7 ± 3 kcal mol-1, ΔHacid(CH3C≡C-H) = 381.1 ± 3 kcal mol-1, and ΔHacid(CH2=C=CH) = 372 ± 5 kcal mol-1. Evidence is provided for the isomerization of the allenyl anion (CH2=C=CH-) to the 1-propynyl anion (CH3C≡C-) in the proton transfer reactions of CH2=C=CH- with CH3OH and CH3CH2OH. This complexity limits the precision of experimental measurements. This study explores the intricacies of determining gas phase acidity values by proton transfer reactions for systems in which isomerization can occur.
Trimethylphosphine: Anion-Molecule Reactions and Acidity in the Gas Phase
Grabowski, Joseph J.,Roy, Paul D.,Leone, Robert
, p. 1627 - 1632 (2007/10/02)
Gas-phase acidity of trimethylphosphine has been investigated at ambient temperature by examining proton-transfer reactions in 40 Pa of helium buffer gas in a Flowing Afterglow instrument.On the basis of the occurence-non-occurence of a number of proton-transfer reactions and the observation of rapid H-D exchange between D2O and the conjugate base of trimethylphosphine, it has been determined that trimethylphosphine is more acidic than water.Quantitative measurements are reported for the reaction of trimethylphosphine with atomic oxygen anion and methoxide.These latter two anions exhibit multiple reaction pathways, one of which is proton transfer.From measurements of the rate coefficients of these two reactions and the relative product yields, it is concluded that the gas-phase acidity of trimethylphosphine is very similar to that of the hydroxyl radical; the recommended value is ΔGoacid(PMe3) 1577 +/- 13kJ mol-1.The derived acidity measurement is in slight contrast to recent theoretical and experimental estimates.Furthermore, it is found that anions which react only slowly with trimethylphosphine by proton transfer can undergo an alternative reaction which corresponds to addition of the neucleophilic anion to trimethylphosphine followed by loss of methane.
Gas-Phase Reactions of Anions with Substituted Silanes
DePuy, C. H.,Bierbaum, Veronica M.,Flippin, L. A.,Grabowski, Josef J.,King, Gary K.,et al.
, p. 5012 - 5015 (2007/10/02)
The gas-phase reactions of fluoride, amide, hydroxide, and methoxide ions with a variety of substituted silanes have been studied by the flowing afterglow technique.Fluoride reacts readily with trimethylsilyl derivatives to displace benzyl, alkenyl, and alkynyl anions.These reactions have also been used to generate specific structural isomers (CH3CC- and CH2C=C=CH-).Anions more basic than phenide ion cannot be produced in this manner, and their parent trimethylsilanes interact with fluoride by more complex mechanisms.Amide, hydroxide, and methoxide ions react with substituted trimethylsilanes by both displacement and proton abstraction whenever an acidic hydrogen is present; in the absence of displaceable groups and acidic hydrogen, the reactions of amide, hydroxide, and methoxide parallel those of fluoride ion.
