Lewis acid complexes rotational barriers

To explain these results, Lee and colleagues " showed that in the absence of Lewis acids the rotational barrier of the C=N double bond is fairly high, but in the presence of catalysts the rotational barrier is lowered. The complex formation of tosylate and AICI3 makes the double bond rotation possible and the product distribution is determined by the relative stability of the oxime E-Z isomers (equation 89). A cychc transition state affords the corresponding quinolinone 281 and the isoquinolinone 282. 

Lee and coworkers ", studying the Beckmann rearrangement of 1-indanone oxime derivatives 240, observed that the pure E and Z oximes isomerize under mild acidic conditions such as silica gel (equation 72). In the presence of Brpnsted or Lewis acids as silica gel or AICI3 the high rotational barrier of C=N double bond would be lowered by the formation of a complex between the tosylate and AICI3 241. This fact makes the... 

Wiberg studied rotational barriers in formaldehyde, propanal and acetone coordinated to Lewis acids such as BFj or AICI3, where all complexes were found to prefer bent geometries. For formaldehyde complexes, linear structures are 6.10kcal/mol higher in energy and out-of-plane structure (Tt-complexes) even higher [10]. 

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