Planar, fused-ring systems, coplanar

The structures of several related naphtho-fused ring systems have been determined by X-ray crystallography. Thus, the cyclic silazane 112 (R = Ph) is planar at the nitrogen atom and all the rings lie almost coplanar, while the related compound 112 (R = Bu but with an anisyl group attached to one of the silicon atoms) has the silicon atoms out of the plane of the tricyclic system, and the ylide 113 has the heterocyclic ring in an envelope conformation and the ylidic carbon is pyramidal and not planar <1996CB495> (see Section 9.18.4.3.2). 

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