Abstract
Abstract Six-membered cyclophosphaeenes, I,3-diaza-and I,3,5-triaza-2-phosphorines are characterized by a dipolar structure of ylide type with & positive charge on phosphorus atom and negative one, delokalized in an azine fragment. In n-donor substituents at a phosphorus atom as well as in electron-acceptor substituents in 4,b heterocycle position this leads to an anomalous ratio of length of formally ordinary exo-cyclic and double endocyclic bonds PNexo > PNendo. Quantum chemical analysis of the situation performed by means of SCF method in CND0/2 approximation reveals more pronounced s-character of nitrogen atoms in exocyclic bonds in comparison to endocycli ones.
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