| Abstract
| - Nucleophilic substitutions by a hydroxide ion at vinylic carbons of methoxyethene (system A),3-methoxypropenal (system B), 2,3-dihydro-4H-pyran-4-one (system C), and 4H-pyran-4-one (systemD) were calculated by Becke's three-parameter hybrid density functional-HF method with the Lee−Yang−Parr correlation functional (B3LYP//B3LYP) and the second-order Møller−Plesset theory(MP2//B3LYP) using the 6-31+G(d) and AUG-cc-pVTZ basis sets. In addition, bulk solvent effects(aqueous solution) were estimated by the polarized continuum (overlapping spheres) model (PCM-B3LYP//B3LYP) and the polarizable conductor PCM model (CosmoPCM-B3LYP//B3LYP). Themechanisms as well as the influence of resonance, cyclic strain, aromatic, and polar effects on thereactivity of the calculated systems were determined. In the gas phase the rate-determining stepof nucleophilic vinylic substitutions by a hydroxide ion may be either addition of hydroxide ion atthe vinylic carbon (systems A and B) or elimination of the leaving group (systems C and D). Inaqueous solution, for all four systems investigated, addition of hydroxide ion at the vinylic carbonis rate determining.
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