Issue 15, 2019

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


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

Article type
27 Dec 2018
15 Mar 2019
First published
18 Mar 2019
This article is Open Access
Creative Commons BY license

Phys. Chem. Chem. Phys., 2019,21, 7924-7931

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

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