TRANSANNULAR INTERACTIONS IN POLYCYCLIC HYDROCARBONS. THE SYSTEM OF CAGE-SHAPED HEXACYCLO[6.6.0.0(2,6).0(3,13).0(4,11).0(5,9)]TETRADECANE DERIVATIVES

摘要

The gas phase He(I alpha) photoelectron spectra (PES) of several ketone and olefinic derivatives of the titled compound are measured. The high energy pi-orbitals (HOMO and SHOMO) of 1e show an unusually large energy splitting of 0.90 eV, while the corresponding n-orbitals of 1d appear to be nearly degenerate (<0.1 eV). The difference between these observations is analyzed with the aid of theoretical models. It is concluded in this work that the pi-pi energy splitting of 1e is derived mainly from an orbital interaction transmitted through-space (TS) across the ring. Since such a nonbonded interaction is sensitive to distance, a conformational analysis of the cycloctane ring moiety of 1e is also performed. As compared to the result of PES, it seems that the ab initio (STO-3G) method is more reliable than AM1, in which the TS interaction is somewhat underestimated. [References: 42]