The electronic structure of 1,2-di(p-tolyl)ethane and of pure and substituted [2.2]paracyclophane

Abstract

Two new ’’spectroscopic’’ CNDO model parametrizations, constructed to describe the electronic excitation spectra of conjugated hydrocarbons, are utilized to analyze these spectra for the double‐benzene‐ring molecules 1,2‐di(p‐tolyl)ethane, [2.2]paracyclophane, pseudopara‐dibromo[2.2]paracyclophane, pseudopara‐dicyano[2.2]paracyclophane, and 1,1,2,2,9,9,10,10 octafluoro[2.2]paracyclophane. Our CNDO/S3 model predicts orbital eigenvalue spectra which are in quantitative (ΔE∼0.1 eV) correspondence with the ultraviolet photoemission spectra of those molecules for which they have been measured. Its predictions of the ultraviolet absorption spectra of 1,2‐di(p‐tolyl)ethane are equally quantitative, although those for the absorption spectra of the [2.2]paracyclophanes are only qualitative (ΔE≲0.3 eV). A major success of the model is its correct prediction of the observed symmetry of the radical anion ESR spectra of 1,2‐di(p‐tolyl)ethane and [2.2]‐paracyclophane: the latter result having eluded prior molecular‐orbital models. Moreover, a substantial alteration in the symmetry of the ESR radical anion spectra is predicted for the case of 1,1,2,2,9,9,10,10 octafluoro‐[2,2]‐paracyclophane relative to [2,2]paracyclophane.