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Issue 2, 2009
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Stepwise walden inversion in nucleophilic substitution at phosphorus

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We have studied the mechanism of SN2@P reactions in the model systems X + PMe2Y and X + POR2Y (with R = Me, OH, OMe; and X, Y = Cl, OH, MeO) using density functional theory at OLYP/TZ2P. Our main purpose is to analyze the nature of the Walden inversion in our model nucleophilic substitution reactions. Walden inversion is well-known to proceed, in general, as a concerted umbrella motion of the substituents at the central atom. Interestingly, we find here that, in certain model reactions, Walden inversion can also proceed in a stepwise fashion in which the individual substituents of the umbrella flip, consecutively, from the educt to the product conformation via separate barriers on the reaction profile. We also examine how variation in nucleophile and leaving group may tune the pentavalent transition structure between labile transition state (TS) and stable transition complex (TC). Furthermore, we explore the various competing multistep pathways in the symmetric (X = Y) and asymmetric (X ≠ Y) substitution reactions in our model reaction systems.

Graphical abstract: Stepwise walden inversion in nucleophilic substitution at phosphorus

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The article was received on 31 Jul 2008, accepted on 18 Sep 2008 and first published on 29 Oct 2008

Article type: Paper
DOI: 10.1039/B813152J
Phys. Chem. Chem. Phys., 2009,11, 259-267

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    Stepwise walden inversion in nucleophilic substitution at phosphorus

    M. A. van Bochove, M. Swart and F. M. Bickelhaupt, Phys. Chem. Chem. Phys., 2009, 11, 259
    DOI: 10.1039/B813152J

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