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Journal ArticleDOI

Recent advances in the energetics and mechanisms of gas-phase ionic reactions

30 Jan 1998-Pure and Applied Chemistry (International Union of Pure and Applied Chemistry)-Vol. 70, Iss: 10, pp 1969-1976

AbstractThree important aspects are still at the forefront of gas-phase ion chemistry: structure and energetics, mechanisms of gas-phase reactions relevant to condensed phases, and bridging the gap between gas-phase and solution. In this paper, we review some recent results of our laboratories: 1) The use of incoherent infrared radiation to promote multiphoton dissociation of ions is shown to be an efficient and convenient method to determine the energetics of ions and provide structural information of ions. 2) New experimental and theoretical data provide some interesting comparison between nucleophilic reactions at carbon, silicon and germanium centers. In the latter cases, the mechanism involves primarily an attachment-detachment process. 3) The ability to make gas-phase anions attached to neutral molecules provides an interesting approach towards the study of the stability, reactivity, structure and spectroscopy of gas-phase solvated ions.

Topics: Molecule (51%), Ionic bonding (51%)

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Journal ArticleDOI
03 May 2002-Science
TL;DR: The finding that the majority of trajectories avoided this potential energy minimum and instead dissociated directly to products and may be applicable to other reactive systems where there is a hierarchy of time scales for intramolecular motions and thus inefficient IVR.
Abstract: Chemical dynamics trajectory simulations were used to study the atomic-level mechanisms of the OH- + CH3F --> CH3OH + F- SN2 nucleophilic substitution reaction. The reaction dynamics, from the [OH...CH3...F]- central barrier to the reaction products, are simulated by ab initio direct dynamics. The reaction's potential energy surface has a deep minimum in the product exit channel arising from the CH3OH...F- hydrogen-bonded complex. Statistical theories of unimolecular reaction rates assume that the reactive system becomes trapped in this minimum and forms an intermediate, with random redistribution of its vibrational energy, but the majority of the trajectories (90%) avoided this potential energy minimum and instead dissociated directly to products. This finding is discussed in terms of intramolecular vibrational energy redistribution (IVR) and the relation between IVR and molecular structure. The finding of this study may be applicable to other reactive systems where there is a hierarchy of time scales for intramolecular motions and thus inefficient IVR.

310 citations


Journal ArticleDOI
Abstract: The B3LYP, BLYP, and BP86 variants of density functional theory, in conjunction with double and triple ζ basis sets, have been examined for SN2 reactions of the type CH3X + F- → CH3F + X- (X = F, C...

100 citations


Journal ArticleDOI
TL;DR: The structures of seven gas phase identity S(N)2 reactions of the form CH(3)X + X(-) have been characterized with seven distinct theoretical methods: RHF, B3LYP, BLYP, BP86, MP2, C CSD, and CCSD(T), in conjunction with basis sets of double and triple zeta quality.
Abstract: The structures of seven gas phase identity SN2 reactions of the form CH3X + X- have been characterized with seven distinct theoretical methods: RHF, B3LYP, BLYP, BP86, MP2, CCSD, and CCSD(T), in conjunction with basis sets of double and triple ζ quality. Additionally, the energetics of said reactions have been definitively computed using focal point analyses utilizing extrapolation to the one-particle limit for the Hartree−Fock and MP2 energies using basis sets of up to aug-cc-pV5Z quality, inclusion of higher order correlation effects [CCSD and CCSD(T)] with basis sets of aug-cc-pVTZ quality, and additional auxiliary terms for core correlation and scalar relativistic effects. Final net activation barriers for the reactions are = −0.8, = 1.6, = 28.7, = 14.3, = 13.8, = 28.6, and = 25.7 kcal mol-1. General trends in the energetics, specifically the performance of the density functionals, and the component energies of the focal point analyses are discussed. The utility of classic Marcus theory as a techniqu...

69 citations


Journal ArticleDOI
Abstract: Ab initio calculations at the HF, MP2, and CCSD(T) levels of theory, utilizing a range of basis sets including the large bases 6-311++G(2df,2pd) and aug-cc-pVTZ, are used to study the OH − +CH 3 F→CH 3 OH+F − potential energy surface (PES). Structures, vibrational frequencies, and energies are determined for the reactant and product asymptotic limits, the OH⋯CH 3 F ion–dipole potential minimum, the [OH⋯CH 3 ⋯F] − central barrier, and the CH 3 OH⋯F − hydrogen-bonded minimum. This PES does not have a post-reaction F − ⋯CH 3 OH minimum complementary to the pre-reaction OH − ⋯CH 3 F minimum. Except for the CH 3 OH⋯F − minimum, the large basis sets and MP2 theory give a consistent set of structures and frequencies for the stationary points. Neither the structure nor the vibrational frequencies of the CH 3 OH⋯F − minimum are converged by the MP2 and large basis set calculations. RHF theory does not describe the energy of the [OH⋯CH 3 ⋯F] − central barrier nor the reaction exothermicity, however, it does give OH − +CH 3 F→OH − ⋯CH 3 F and F − +CH 3 OH→CH 3 OH⋯F − well depths in good agreement with the CCSD(T) values. Overall good agreement is found between the MP2/6-31+G ∗ and much higher level CCSD(T) energies for the stationary points. The MP2 and CCSD(T) calculations give a reaction exothermicity and F − +CH 3 OH→CH 3 OH⋯F − well depth in good agreement with the experimental values.

23 citations


Journal ArticleDOI
TL;DR: This review is focused on ESI-MS studies of copper-catalyzed reactions, and the plethora of mass spectrometric approaches demonstrated is demonstrated on copper mediated C-H activations, cross coupling reactions, rearrangements, organocuprate chemistry, and other examples.
Abstract: Electrospray ionization mass spectrometry (ESI-MS) is becoming an important tool for mechanistic studies in organic and organometallic chemistry. It allows investigation of reaction mixtures including monitoring of reactants, products, and intermediates, studying properties of the intermediates and their reactivity. Studying the reactive species in the gas phase can be advantageously combined with theoretical calculations. This review is focused on ESI-MS studies of copper-catalyzed reactions. Possible effects of the electrospray process on the transfer of the copper complexes to the gas phase are discussed. The plethora of mass spectrometric approaches is demonstrated on copper mediated C-H activations, cross coupling reactions, rearrangements, organocuprate chemistry, and other examples. © 2015 Wiley Periodicals, Inc. Mass Spec Rev 35: 85–110, 2016.

19 citations


References
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Book
01 Jan 1988
Abstract: Ion cyclotron resonance spectrometry Fourier transform mass spectrometry neutral products from electron bombardment flow studies flowing afterglow and sift pulsed electron high pressure mass spectrometer nuclear decay techniques ion beam methods state-selected and state-to-state ion-molecules reaction dynamics by photo-ionization methods spectroscopic probes infrared laser photolysis pulsed methods for cluster ion spectroscopy.

282 citations