In this work we present a study on the theoretical determination of reactivity and structures of complex phosphorus heterocycles. Applying the Fukui function and dual reactivity descriptors surprising rearrangement reactions and reactivities of a phosphorus bicycle are explained and, also the hitherto not completely understood structure of the main starting compound with a very short non-bonding C-C-distance is described as a fast equilibrium in solid state rather than as non-classical ylid. Aspects on negative values of Fukui functions found in some structures are discussed. (C) 2020 Published by Elsevier B.V.