Roustam Gareyev

Photoelectron spectroscopy, gas phase acidity, and thermochemistry of tert-butyl hydroperoxide: Mechanisms for the rearrangement of peroxyl radicals

The 3.531 eV negative ion photoelectron spectra of the hydroperoxide ion and the tert-butylperoxide ion have been studied. We find HO2−+ℏω351.1 nm→HO2+e− EA[HO2,X 2A″]=1.089±0.006 eV, (CH3)3COO−+ℏω351.1 nm→(CH3)3COO+e− EA[(CH3)3COO,X 2A″]=1.196±0.011 eV. The photoelectron spectra show detachment to the ground state of the peroxyl radicals and to a low lying electronic state. The intercombination gaps are measured to be ΔE(X 2A″–A 2A′)[HO2]=0.871±0.007 eV and ΔE(X 2A″–2A′)[(CH3)3COO]=0.967±0.011 eV. The gas phase acidity of (CH3)3COOH was measured in a tandem flowing afterglow-selected ion flow tube (FA-SIFT) to be ΔacidG298=363.2±2.0 kcal mol−1 and we find ΔacidH298[(CH3)3COO–H]=370.9±2.0 kcal mol−1. Use of ΔacidH298[(CH3)3COO–H] and EA[(CH3)3COO] leads to the bond energies DH298[(CH3)3COO–H]=85±2 kcal mol−1 and D0[(CH3)3COO–H]=83±2 kcal mol−1. The thermochemistry of the alkylperoxyl radicals, RO2, is reviewed. A mechanism for the rearrangement of chemically activated peroxyl radicals is proposed [RO2...

Gas phase reactions of NH2Cl with anionic nucleophiles: nucleophilic substitution at neutral nitrogen.

Reactions of chloramine, NH2Cl, with HO−, RO− (R = CH3, CH3CH2, CH3CH2CH2, C6H5CH2, CF3CH2), F−, HS−, and Cl− have been studied in the gas phase using the selected ion flow tube technique. Nucleophilic substitution (SN2) at nitrogen to form Cl− has been observed for all the nucleophiles. The reactions are faster than the corresponding SN2 reactions of methyl chloride; the chloramine reactions take place at nearly every collision when the reaction is exothermic. The thermoneutral identity SN2 reaction of NH2Cl with Cl−, which occurs approximately once in every 100 collisions, is more than two orders of magnitude faster than the analogous reaction of CH3Cl. The significantly enhanced SN2 reactivity of NH2Cl is consistent with a previous theoretical prediction that the barrier height for the SN2 identity reaction at nitrogen is negative relative to the energy of the reactants, whereas this barrier height for reaction at carbon is positive. Competitive proton abstraction to form NHCl− has also been observed with more highly basic anions (HO−, CH3O−, and CH3CH2O−), and this is the major reaction channel for HO− and CH3O−. Acidity bracketing determines the heat of deprotonation of NH2Cl as 374.4 ± 3.0 kcal mol−1.

Generation and assay of C6HxD(7-x)+ (x = 1–6) benzenium ions: a flowing afterglow-selected ion flow tube study

Abstract An experimental study of protonated benzene in the gas phase in reported, stimulated by the recent suggestion of a face centered π-complex structure as the most stable form of protonated benzene. C6HxD(7-x)+ ions have been formed either by protonation of C6D6 by H3O+ and ensuing H/D exchange reactions with H2O or by the mirror isotope reaction of C6D6 with D3O+/D2O. Their assay by two sampling methods, H+/D+ transfer to strong bases and collisionally activated dissociation, was found consistent with a σ-complex species.

The Gas-Phase Reactions of the Allenyl Anion with CS2, COS and CO2

Abstract The allenyl anion reacts readily in the gas phase with CS2 and COS to form the thioketenyl anion. The reaction involves a complex series of cyclization and ring-opening reactions in which the central carbon of allene and the carbon of the neutral reagent become equivalent. Despite the complexity, the reaction with CS2 is useful in determining the site of deprotonation of unsymmetrical allenes. The reaction of the allenyl anion with CO2 produces only an adduct, because the cleavage reaction to the ketenyl anion and ketene is endothermic. However, the allenyl anion is produced if the reaction is carried out in the reverse direction.

Mechanisms of reactions of BH2+, HBOH+, and H2BOH2+ with H2O. An experimental gas phase isotope labeling and theoretical ab initio study

Abstract The reactions of BH2+, HBOH+, and H2BOH2+ with H2O have been studied in the gas phase by using a tandem flowing afterglow-selected ion flow tube apparatus. Proton transfer to H2O has been observed in the reactions with HBOH+ and H2BOH2+; addition and elimination of a hydrogen molecule occurs in the reaction with BH2+. The mechanisms of these reactions have been elucidated by labeling the reagents with deuterium and 18O isotopes. An alternative pathway for proton transfer from HBOH+ and H2BOH2+ to H2O has been observed, which involves intermediate formation of a boron-oxygen bound adduct and scrambling of oxygen atoms within it. The proposed mechanisms are supported by ab initio theoretical calculations that have been carried out at Moller–Plesset (MP2) (full)/6–311G(d, p) level. Rate constants for the reactions have been measured and found to be close to theoretical collision rates in the gas phase.