Fifty years of nucleophilic substitution in the gas phase

Abstract

Bimolecular nucleophilic substitution (S 2 N ) reactions have become a model system for the investigation of structure-reactivity relationships, stereochemistry, solvent influences, and detailed atomistic dynamics. In this review, the progress during five decades of experimental and theoretical research on gas phase S 2 N reactions is discussed. Many advancements of the employed methods have led to a tremendous increase in our understanding of the properties and the dynamics of these reactions. For reactions involving six atoms a quantitative agreement of the differential reactive scattering cross sections has already been achieved, in the future it is expected that even larger polyatomic reactions systems become tractable. Furthermore, studies with higher precision, improved reactant control, and a more accurate theoretical treatment of quantum effects are envisioned.

Conformer-specific polar cycloaddition of dibromobutadiene with trapped propene ions

“…In combination with mass-spectrometric tools, this capability opens up a wide range of opportunities for the precise investigation and validation of reaction mechanisms. Solvent effects, which may affect the mechanism in solution-phase and were not included in the present gas-phase study, could in principle be accounted for by using microsolvated reagents as has been demonstrated previously, for instance, in gas-phase mechanistic studies of S N 2 reactions 40 .…”

Uncovering an oxide ion substitution for the OH− + CH3F reaction

“…The traditional picture of the SN2 reactions was described by Ingold and co-workers more than 80 years ago, 1,2 and since then these reactions have always been in the focus of the scientific interest. [3][4][5][6][7][8][9][10][11][12][13][14][15][16] In a schematic X − + CH3Y → CH3X + Y − SN2 reaction, the widelyknown Walden inversion usually occurs as follows: In the entrance channel the reactants form an ion-dipole X − •••CH3Y complex, then a [X•••CH3•••Y] − transition state can be found, which finally leads to a XCH3•••Y − complex in the product channel. The above presented mechanism inverts the configuration of the CH3Y reactant, due to the umbrella motion of the CH3 group.…”

Validating Experiment for the Reaction H2 + NH2- by Dynamical Computations on an Accurate Full-Dimensional Potential Energy Surface

“…One can see that, the ICSs ( 2 H j 0  ) drops rapidly at low collision energy and then becomes almost flat at Ec ≥ 5 kcal/mol, which is general in barrierless ion-molecule reactions. [54][55][56][57] In contrast, for H2 (j=1), ICSs are dramatically lower than the ICSs of 2 H j 0  , particularly at low collision energies. For H2 (j=2), the ICSs are even lower.…”