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New Proposed Proton-abstracted Roundabout with Backside Attack Mechanism for the SN2 Reaction at Nitrogen Center F⁻+ NH2Cl

Abstract

Recent studies have improved our understanding of the mechanism and dynamics of bimolecular nucleophilic substitution (SN2) reaction at carbon center. Nonetheless, the SN2 reaction at nitrogen center has received less attention and is less understood. Here, we propose a new reaction mechanism for the SN2 reaction at nitrogen center F⁻ + NH2Cl using ab initio molecular dynamics calculations. The new proposed mechanism involves the rotation of NHCl with one proton of NH2Cl abstracted by the nucleophile, followed by a classical, backside-attack process. A double-inversion mechanism, first revealed recently for the SN2 reaction at carbon center, is also observed for the title reaction at nitrogen center. In contrast to the F⁻ + CH3Cl with a proton-abstraction induced first inversion transition state, the F⁻ + NH2Cl is a hydrogen-bond induced inversion. The new proposed reaction mechanism opens a reaction channel to avoid the proton-abstraction mechanism at low collision energy. The double-inversion mechanism of the title reaction with a negative first-inversion transition is expected to have a larger contribution to the reaction rate than the F⁻ + CH3Cl with a positive first-inversion transition state.

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Publication details

The article was received on 22 Feb 2018, accepted on 23 Mar 2018 and first published on 04 Apr 2018


Article type: Paper
DOI: 10.1039/C8CP01201F
Citation: Phys. Chem. Chem. Phys., 2018, Accepted Manuscript
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    New Proposed Proton-abstracted Roundabout with Backside Attack Mechanism for the SN2 Reaction at Nitrogen Center F⁻+ NH2Cl

    Y. Li and D. Wang, Phys. Chem. Chem. Phys., 2018, Accepted Manuscript , DOI: 10.1039/C8CP01201F

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