PHOTOCHEMICAL ACTIVATION OF DISTAL FUNCTIONAL GROUPS IN POLYFUNCTIONAL MOLECULES - PHOTOCHEMISTRY AND PHOTOPHYSICS OF THE SYN-7- AND ANTI-7-CHLOROBENZONORBORNENES

摘要

The spectroscopic (electronic absorption, fluorescence, and electron transmission (ET)) and photochemical properties of anti-7-chlorobenzonorbornene (BAntiCl) and syn-7-chlorobenzonorbornene (BSynCl) are reported. These are complemented by ab initio MO calculations. The BSynCl isomer, the LUMO of which contains relatively little C-Cl sigma* character, is relatively unreactive upon photolysis (254 nm) in methanol (Phi(dis)(BSynCl) = 0.0014). The LUMO of BAntiCl is calculated to contain a significant amount of C-Cl sigma* character, consistent with the much greater reactivity (Phi(dis)(BAntiCl) = 0.23) of this isomer. The ET spectra reveal that the pi* levels of these compounds and of their exo-2- and endo-2-chlorobenzonorbornene isomers (BExoCl and BEndoCl, respectively) are appreciably stabilized relative to that of benzonorbornene (BNB). A natural bond orbital (NBO) analysis shows that much of this stabilization derives from inductive effects, with sizable through-space (TS) (0.07 and 0.10 eV) and through-bond (TB) (0.03 and 0.06 eV) coupling between the pi* and C-CI sigma* orbitals for BAntiCl and BExoCl, respectively. [References: 40]