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Solid-phase Synthesis of [4.4] Spirocyclic Oximes
Published on: February 6, 2019
Thorpe-Ingold acceleration of oxirane formation is mostly a solvent effect
Jakub Kostal1, William L Jorgensen
1Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520-8107, USA.
The Thorpe-Ingold hypothesis explains the gem-dimethyl effect in cyclization reactions. Computational studies show solvent effects, not intrinsic reactivity, drive the observed rate increases with alpha-methylation.
Area of Science:
- Computational Chemistry
- Organic Reaction Mechanisms
- Physical Chemistry
Background:
- The Thorpe-Ingold hypothesis describes the gem-dimethyl effect in cyclization reactions.
- Investigating the influence of alpha-methylation on the reactivity of 2-chloroethoxide derivatives.
Purpose of the Study:
- To computationally investigate the Thorpe-Ingold hypothesis for the gem-dimethyl effect.
- To determine the role of intrinsic reactivity versus solvent effects in observed rate accelerations.
Main Methods:
- Ab initio MP2/6-311+G(d,p) and CBS-Q calculations.
- Continuum hydration and mixed quantum/statistical mechanics (MC/FEP) simulations with explicit hydration.
- Analysis of computational results in both gas and aqueous phases.
Main Results:
- Little intrinsic difference in reactivity was found with increasing alpha-methylation in the gas phase.
- Simulations including hydration effects reproduced experimentally observed rate increases.
- Increased steric hindrance to hydration of the nucleophilic oxygen atom was identified as the primary cause of rate acceleration.
Conclusions:
- The gem-dimethyl acceleration of oxirane formation is predominantly a solvent effect.
- Steric hindrance to hydration, influenced by alpha-methylation, explains the Thorpe-Ingold effect.
- Computational modeling is crucial for understanding complex reaction mechanisms and solvent interactions.
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