41866-81-3Relevant academic research and scientific papers
Determination of the gas-phase acidities of halogen-substituted aromatic compounds using the silane-cleavage method
Wenthold,Squires
, p. 17 - 24 (1995)
The gas-phase acidities of halogen-substituted aromatic compounds have been determined in a flowing afterglow-triple quadrupole apparatus with use of the silane cleavage method developed by DePuy and co-workers [C. H. DePuy, S. Gronert, S. E. Barlow, V. M. Bierbaum and R. Damrauer, J. Am. Chem. Sec., 111, 1968 (1989)]. In this method the relative yields of siloxide ion products produced in reactions of OH- with trimethylsilyl- or phenyidimethylsilyl-substituted aromatic compounds are correlated with the difference in gas-phase acidity of the accompanying neutral products. Acidities are reported for different ring-positions in fluoro-, chloro- and bromobenzene, chloro- and bromonaphthalene and benzyl chloride. Excellent precision is achieved in most cases, with assigned uncertainties less than 23 kcal/mol. Goad agreement is obtained between the acidities determined with use of two different types of silane precursor. Halogen-substitution increases the gas-phase acidities of benzene and naphthalene by similar amounts (13-14 kcal/mol). The effects on different ring-positions in benzene and naphthalene are shown to be primarily inductive in nature, falling-off by a consistent 2.5-3.5 kcal/mol per bond separating the acidic site from the haloges-bearing carbon in the chlorine and bromine-substituted systems. Larger effects are evident in the positional acidities of fluorobenzene. The meta and pava position acidities of halobenzenes are shown to be linearly correlated with the acidities of the corresponding meta and pava halophenols, haloanilines and halotoluenes.
Dimethylsilanone Enolate Anion: Competitive Fragmentation and Electron Autodetachment of Vibrationally Excited Siloxide Anions in the Gas Phase
Tumas, William,Salomon, Karen E.,Brauman, John I.
, p. 2541 - 2546 (1986)
Infrared multiple photon photochemical studies of gas-phase siloxide anions trapped in an ion cyclotron resonance spectrometer are reported.Upon CO2 laser irradiation, trimethylsiloxide anion, 1, and dimethylsiloxide anion, 3, eliminate methane and molecular hydrogen, respectively, resulting in the production of dimethylsilanone enolate anion, the silicon-containing analogue of acetone enolate anion.These fragmentation reactions are analogous to the unimolecular decompositions of gas-phase alkoxide anions which react via a stepwise mechanism involving initial heterolytic cleavage to an intermediate anion-ketone complex and a subsequent proton-transfer reaction within the ion-molecule complex.Extension of this mechanism to the siloxide systems suggests that dimethylsilanone is an intermediate in the decomposition.In contrast to the alkoxides, vibrationally excited siloxide anions also undergo electron loss (vibrationally induced electron detachment, VED).The use of both high-power pulsed and low-power continuous-wave (CW) CO2 lasers provides access to both available reaction channels and aids in the elucidation of the primary photochemical events.For 1, pulsed laser activation results in both methane elimination and VED, while activation with the CW laser leads to electron loss exclusively.Products resulting from both fragmentation and electron detachment are observed for 3 activated by either laser.A significant contribution from secondary photochemistry was found in the pulsed laser-induced reactions of 3.The observation of direct photochemical branching between fragmentation (H2 elimination) and electron detachment (VED) in the CW laser photolysis of 3 provides an estimate of 62 kcal/mol as an upper limit for the silicon-oxygen ? bond energy in dimethylsilanone.
Gas- Phase Ion Chemistry of Siloxide and Silamide Ions by Using the Flowing Afterglow. Unusual Rearrangements Involving SiO and SiS Bond Formation
O'Hair, Richard A.J.,Sheldon, John C.,Bowie, John H.,Damrauer, Robert,DePuy, Charles H.
, p. 489 - 496 (2007/10/02)
Siloxide ions undergo O/S exchange reactions with suitable sulfur-containing neutrals, e.g.H3SiO- + CS2 -> H3SiS- + COS.Silamide ions similarly undergo NR/O and NR/S exchange reactions together with nucleophilic displacement reactions, e.g.: .No simple correlation between rate and mechanism is observed for all the studied reactions.
The Gas-Phase Acidities of the Alkanes
DePuy, Charles H.,Gronert, Scott,Barlow, Stephan E.,Bierbaum, Veronica M.,Damrauer, Robert
, p. 1968 - 1973 (2007/10/02)
The gas-phase acidities of 15 simply alkanes have been determined in a flowing afterglow-selected ion flow tube (FA-SIFT) by a kinetic method in which alkyltrimethylsilanes are allowed to react with hydroxide ions to produce a mixture of trimethylsiloxide ions by loss of alkane and alkyldimethylsiloxide ions by loss of methane.The reaction is proposed to proceed by addition of hydroxide ion to the silane to form a pentacoordinate siliconate ion intermediate which decomposes through two transition states, one in which negative charge is placed on a methyl group and the other in which negative charge is placed on the alkyl group.The ratio of siloxide ions produced is proposed to be correlated to the relative basicity of the methyl and alkyl anions.The method is calibrated by making use of the known acidities of methane (ΔH0acid=416.6 kcal/mol) and benzene (ΔH0acid= 400.7 kcal/mol).In general, methyl substitution is found to stabilize alkyl anions in the gas phase except that the ethyl anion is found to be more basic that the methyl anion.By combining the gas-phase acidities with the bond dissociation energies, the electron affinities (EA) of the corresponding alkyl radicals can be calculated.Many simple alkyl radicals are found to have negative EA's.The results for the alkyl groups studied are as follows, where the first number is the ΔH 0acid (kcal/mol) of the corresponding alkane and the second number (in parentheses) is the EA (kcal/mol) of the alkyl radical: ethyl 420.1 (-6.4), isopropyl 419.4 (-9.5), cyclobutyl 417.4 (-7.5), cyclopentyl 416.1 (-7.0), sec-butyl 415.7 (-5.8), n-propyl 415.6 (-1.9), tert-butyl 413.1 (-5.9), isobutyl 412.9 (0.8), 3-butenyl 412.0 (1.7), cyclopropyl 411.5 (8.4), cyclopropylmethyl 410.5 (3.2), 1-methylcyclopropyl 409.2 (8.0), neopentyl 408.9 (4.8), vinyl 407.5 (16.1), 2-propenyl 405.8 (15.8).
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.
