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Issue 15, 2019

Rethinking the X + CH3Y [X = OH, SH, CN, NH2, PH2; Y = F, Cl, Br, I] SN2 reactions

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Abstract

Moving beyond the textbook mechanisms of bimolecular nucleophilic substitution (SN2) reactions, we characterize several novel stationary points and pathways for the reactions of X [X = OH, SH, CN, NH2, PH2] nucleophiles with CH3Y [Y = F, Cl, Br, I] molecules using the high-level explicitly-correlated CCSD(T)-F12b method with the aug-cc-pVnZ(-PP) [n = D, T, Q] basis sets. Besides the not-always-existing traditional pre- and post-reaction ion-dipole complexes, X⋯H3CY and XCH3⋯Y, and the Walden-inversion transition state, [X–CH3–Y], we find hydrogen-bonded X⋯HCH2Y (X = OH, CN, NH2; Y ≠ F) and front-side H3CY⋯X (Y ≠ F) complexes in the entrance and hydrogen-bonded XH2CH⋯Y (X = SH, CN, PH2) and H3CX⋯Y (X = OH, SH, NH2) complexes in the exit channels depending on the nucleophile and leaving group as indicated in parentheses. Retention pathways via either a high-energy front-side attack barrier, XYCH3, or a novel double-inversion transition state, XH⋯CH2Y, having lower energy for X = OH, CN, and NH2 and becoming submerged (barrier-less) for X = OH and Y = I as well as X = NH2 and Y = Cl, Br, and I, are also investigated.

Graphical abstract: Rethinking the X− + CH3Y [X = OH, SH, CN, NH2, PH2; Y = F, Cl, Br, I] SN2 reactions

Supplementary files

Article information


Submitted
27 Dec 2018
Accepted
15 Mar 2019
First published
18 Mar 2019

This article is Open Access

Phys. Chem. Chem. Phys., 2019,21, 7924-7931
Article type
Paper

Rethinking the X + CH3Y [X = OH, SH, CN, NH2, PH2; Y = F, Cl, Br, I] SN2 reactions

D. A. Tasi, Z. Fábián and G. Czakó, Phys. Chem. Chem. Phys., 2019, 21, 7924 DOI: 10.1039/C8CP07850E

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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