Dynamics Effects on an E2/E1cb Borderline Mechanism: Unimolecular Elimination of 2-Aryl-3-chloro-2-R-propanols
✍ Scribed by Shuhei Itoh; Prof. Hiroshi Yamataka
- Publisher
- John Wiley and Sons
- Year
- 2010
- Tongue
- English
- Weight
- 714 KB
- Volume
- 17
- Category
- Article
- ISSN
- 0947-6539
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✦ Synopsis
Abstract
The mechanistic dichotomy between concerted E2 and stepwise E1cb of the base‐promoted elimination of 2‐aryl‐3‐chloro‐2‐R‐propanols was examined computationally at the HF, M05‐2X, and MP2 levels of theory. Optimizations of transition states (TSs) and reaction intermediates, and intrinsic reaction coordinates (IRC) calculations showed that there was a single reaction route for each substrate, and that the mechanism could be changed from E2 to E1cb by making a carbanion intermediate more stable through the introduction of electron‐withdrawing substituents. Molecular dynamics simulations revealed that trajectories started at a single TS led directly to two product regions; the carbanion intermediate region in the E1cb mechanism, and the alkene product region in the E2 mechanism, through path bifurcation after the TS. The present system is a new example of bifurcation in reactions of closed‐shell molecules. The overall reaction mechanism changes dynamically from E2 to E1cb by a gradual change in the ratio of E2 and E1cb trajectories, rather than a path switch in concurrent pathways.