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Ab initio molecular dynamics studies on substitution vs electron transfer reactions of substituted ketyl radical anions with chloroalkanes: how do the two products form in a borderline mechanism?
Author(s) -
Yamataka Hiroshi,
Aida Misako,
Dupuis Michel
Publication year - 2003
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.610
Subject(s) - chemistry , ketyl , ab initio , steric effects , electron transfer , computational chemistry , reactivity (psychology) , ab initio quantum chemistry methods , reaction mechanism , photochemistry , stereochemistry , molecule , organic chemistry , benzophenone , catalysis , pathology , medicine , alternative medicine
We present a qualitative analysis, based on ab initio molecular dynamics (MD) calculations, of the S N 2/ET mechanistic spectrum for three reactions: (1) HC(CN)O· − + CH 3 Cl, (2) HC(CN)O· − + (CH 3 ) 2 CHCl and (3) H 2 CO· − + CH 3 Cl, passing through their S N 2‐like transition states. Finite temperature (298 K) direct MD simulations indicate that the trajectories for reaction (1) appear to have a propensity towards S N 2 products, the propensity for trajectories for reaction (2) seems to be towards ET products, whereas trajectories for reaction (3) appear to show no particular propensity towards either ET or S N 2 products. The mechanistic diversity is consistent with the electron‐donating ability of the ketyl species and steric bulkiness of chloroalkanes. We find that the trajectories have characteristics that reflect strongly the types of process [ S N 2 trajectories in reactions (1) and (3) vs ET trajectories in reactions (2) and (3)]. Trajectories that lead to S N 2 products are simple with C—C bond formation and C—Cl bond breaking essentially completed within 50 fs. By contrast, trajectories leading to ET products are more complex with a sudden electron reorganization taking place within 15–30 fs and the major bonding changes and electron and spin reorganizations completed after 250 fs. Copyright © 2003 John Wiley & Sons, Ltd.