PROPELLA[3(4)] PRISMANE AND ITS CONGENERS - A MO-THEORETICAL STUDY

The geometries of a fourfold bridged tricyclo[4.2.0.0(2,5)]octa-3,7-diene (1) and its photoproducts 2 and 3 were calculated by Hartree-Fock ab initio (3-21G and DZP basis) and semiempirical (MNDO, AM1, MINDO/3) methods. It was found that due to the smaller distance between the double bonds in 1 (2.65 Angstrom) as compared to the parent tricyclo[4.2.0.0(2,5)]octa-3,7-diene (4) (2.91 Angstrom), the sequence of the frontier orbitals is different. In the case of 1, the photochemical [2 + 2]cycloaddition is allowed, whereas in 4 it is forbidden. (C) 1995 by John Wiley and Sons, Inc.