The 3.531 eV negative ion photoelectron spectra of the hydroperoxide ion and the tert-butylperoxide ion have been studied. We find HO 2 Ϫ ϩប 351.1 nm →HO 2 ϩe Ϫ EA͓HO 2 ,X 2 AЉ͔ ϭ1.089Ϯ0.006 eV, ͑CH 3 ͒ 3 COO Ϫ ϩប 351.1 nm →͑CH 3 ͒ 3 COOϩe Ϫ EA͓͑CH 3 ͒ 3 COO,X 2 AЉ]ϭ1.196 Ϯ0.011 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 ⌬E(X 2 AЉ-Ã 2 AЈ)͓HO 2 ͔ϭ0.871Ϯ0.007 eV and ⌬E(X 2 AЉ-2 AЈ)͓͑CH 3 ͒ 3 COO͔ϭ0.967Ϯ0.011 eV. The gas phase acidity of ͑CH 3 ͒ 3 COOH was measured in a tandem flowing afterglow-selected ion flow tube ͑FA-SIFT͒ to be ⌬ acid G 298 ϭ363.2Ϯ2.0 kcal mol Ϫ1 and we find ⌬ acid H 298 ͓͑CH 3 ͒ 3 COO-H͔ϭ370.9Ϯ2.0 kcal mol Ϫ1. Use of ⌬ acid H 298 ͓͑CH 3 ͒ 3 COO-H͔ and EA͓͑CH 3 ͒ 3 COO͔ leads to the bond energies DH 298 ͓͑CH 3 ͒ 3 COO-H͔ϭ85Ϯ2 kcal mol Ϫ1 and D 0 ͓͑CH 3 ͒ 3 COO-H͔ϭ83Ϯ2 kcal mol Ϫ1. The thermochemistry of the alkylperoxyl radicals, RO 2 , is reviewed. A mechanism for the rearrangement of chemically activated peroxyl radicals is proposed ͓RO 2 ͔X 2 AЉ→͓RO 2 ͔*Ã 2 AЈ→aldehydes/ketonesϩHO(2 ⌸), ͓RO 2 ͔X 2 AЉ→͓RO 2 ͔*Ã 2 AЈ →alkenesϩHO 2 (X 2 AЉ).
The reactions of BH2
+ with hydrogen and
some simple hydrocarbons and hydrides have been studied
in the gas phase with a tandem flowing afterglow-selected ion flow tube
apparatus. Reaction rate constants
are reported along with branching ratios for multichannel reactions.
The mechanisms of reactions have been
elucidated by using deuterium labeling experiments and post-SCF level
molecular orbital calculations. A
general mechanism for the reaction BH2
+ +
RH → HBR+ + H2 (R = OH,
NH2, SH, CH3, C2H5,
C2H3, C2H)
is suggested along with alternative and secondary pathways.
Predicted intermediates have been generated by
independent approaches. The unusual species
BH4
+ and BH6
+ have
been generated and their structures assessed
computationally. The role of BH4
+ in the
isotope exchange reaction of BH2
+ with
D2 is discussed in detail.
Parallels are drawn between reactions of
BH2
+ and CH3
+ in
the gas phase and differences are revealed and
discussed.
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 (S(N)2) at nitrogen to form Cl- has been observed for all the nucleophiles. The reactions are faster than the corresponding S(N)2 reactions of methyl chloride; the chloramine reactions take place at nearly every collision when the reaction is exothermic. The thermoneutral identity S(N)2 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 S(N)2 reactivity of NH2Cl is consistent with a previous theoretical prediction that the barrier height for the S(N)2 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).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.