Abstract
Dynamic NMR methods are used to study 3-substituted benzocycloheptene derivatives, useful models for investigating the conformational effect of the stereoelectronic π–σ* orbital interaction. The 11 compounds studied are divided in two subgroups, the first one containing mainly halogenated derivatives (F, Cl, Br, and OCH3) and the second consisting of oxy derivatives (OCH3, OCH2CH3, OCH=CH2, OAc, p-OPh-R, where R = H, OCH3, and NO2). The results for the first series show the presence of two chair conformations (Ca and Ce) characterized by a decreasing Ca population with increasing electronegativity of the substituent. This trend suggests the presence of a dominant π–σ* interaction for Cl and Br stabilizing the Ca form. The larger Ce population observed for F suggests that a strong attractive interaction with the aromatic peri hydrogen is present in this compound. Finally, in the oxy-substituent series, the populations trend does not correspond to that predicted from the π–σ* orbital interaction, but the individual population perturbations appear to be caused primarily by electrostatic interactions involving the nonsymmetrical polar substituents. Keywords: low temperature NMR, conformational analysis, seven-membered rings, orbital interactions, benzocycloheptene derivatives.
Publisher
Canadian Science Publishing
Subject
Organic Chemistry,General Chemistry,Catalysis
Cited by
4 articles.
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