Chiroptical properties of 12,15-dichloro[3.0]orthometacyclophane - correlations between molecular structure and circular dichroism spectra of a biphenylophane

The valence excited electronic states and the circular dichroism (CD) spect ra of the recently synthesized 12,15-dichloro[3.0]orthometacyclophane 1 are discussed by means of quantum chemical calculations which combine density functional theory with the single-excitation configuration interaction appr oach (DFT/SCI). The X-ray structure of this highly strained biphenylophane is presented. In order to investigate the influence of the cyclophane-type distortions on the CD spectrum of 1, the CD spectra of three model geometri es (2a-2c) are also calculated. It appears that the CD spectrum of the biph enylophane 1 differs substantially from that of the corresponding unstraine d biphenyl 2c. Furthermore, it is found that the pyramidalization of the br idging atoms of the cyclophane ring is an important factor for the red shif t of the first bland with respect to that of an unstrained benzene chromoph ore. (C) 1999 Elsevier Science Ltd. All rights reserved.