Competing E2 and SN2 Mechanisms for the F- + CH3CH2I Reaction

Li Yang, Jiaxu Zhang, Jing Xie, Xinyou Ma, Linyao Zhang, Chenyang Zhao, William L. Hase

Research output: Contribution to journalArticlepeer-review

13 Scopus citations

Abstract

Anti-E2, syn-E2, inv-, and ret-SN2 reaction channels for the gas-phase reaction of F- + CH3CH2I were characterized with a variety of electronic structure calculations. Geometrical analysis confirmed synchronous E2-type transition states for the elimination of the current reaction, instead of nonconcerted processes through E1cb-like and E1-like mechanisms. Importantly, the controversy concerning the reactant complex for anti-E2 and inv-SN2 paths has been clarified in the present work. A positive barrier of +19.2 kcal/mol for ret-SN2 shows the least feasibility to occur at room temperature. Negative activation energies (-16.9, -16.0, and -4.9 kcal/mol, respectively) for inv-SN2, anti-E2, and syn-E2 indicate that inv-SN2 and anti-E2 mechanisms significantly prevail over the eclipsed elimination. Varying the leaving group for a series of reactions F- + CH3CH2Y (Y = F, Cl, Br, and I) leads to monotonically decreasing barriers, which relates to the gradually looser TS structures following the order F > Cl > Br > I. The reactivity of each channel nearly holds unchanged except for the perturbation between anti-E2 and inv-SN2. RRKM calculation reveals that the reaction of the fluorine ion with ethyl iodide occurs predominately via anti-E2 elimination, and the inv-SN2 pathway is suppressed, although it is energetically favored. This phenomenon indicates that, in evaluating the competition between E2 and SN2 processes, the kinetic or dynamical factors may play a significant role. By comparison with benchmark CCSD(T) energies, MP2, CAM-B3LYP, and M06 methods are recommended to perform dynamics simulations of the title reaction.

Original languageEnglish (US)
Pages (from-to)1078-1085
Number of pages8
JournalJournal of Physical Chemistry A
Volume121
Issue number5
DOIs
StatePublished - Feb 9 2017

Bibliographical note

Funding Information:
This material is based on work supported by the National Natural Science Foundation of China (Nos. 21573052, 21403047, 51536002), the Fundamental Research Funds for the Central Universities, China (AUGA5710012114 5710012014), and the Open Project of Beijing National Laboratory for Molecular Sciences (No. 20140103, 20150158). The research at Texas Tech University was supported by the Robert A. Welch Foundation under Grant No. D-0005.

Publisher Copyright:
© 2017 American Chemical Society.

Copyright:
Copyright 2017 Elsevier B.V., All rights reserved.

Fingerprint Dive into the research topics of 'Competing E2 and S<sub>N</sub>2 Mechanisms for the F<sup>-</sup> + CH<sub>3</sub>CH<sub>2</sub>I Reaction'. Together they form a unique fingerprint.

Cite this