The geometries of pagodanes were optimized by the MNDO procedure. The anal. of atomic charges and MO compns. obtained from ab initio calcns. shows that the properties of pagodane are similar to those of its diene valence isomer and that the 4 central C atoms in pagodanes may be more active in chem. reactions. A 4-center/2-electron delocalized system is formed in the plane of the 4 central carbons in pagodane dication, which resembles the cyclobutane dication. Bond strain in pagodanes is much less than in small propellanes, which are not stable. This can explain the rigidity and stability of pagodane framework.

Key words: STABILITY, ELECTRONIC STRUCTURE, AB INITIO CALCULATION, CONFIGURATION, TENSION, STIFF PROBLEM, OPTIMIZATION, MNDO METHOD