Spatial structure heterocyclic organoelement compounds determined by X-raydiffraction. Interpretation model based on hyperconjugative interactions

The interpretation model of the molecular geometry derived from X-ray diffr action data, which gives good results in the structures of symmetric 1,3,2- dioxa- and diaza-phosphacyclanes, is extended on the new classes of non-sym metric sterically hindered structures of 5,6-benzo-1,2-oxaphosphorines, 6,7 -benzo-1,3,2- and 1,4,2-dioxa; and oxaza-phosphepines. It is shown, that st eric ineractions may invert the anomeric effect of substituents. The observ ed changes of bond lengths are explained by electron density transfer as a result of hyperconjugative electronic interactions. The interpretation mode l is supported by the results of analysis of more than 30 structures.