Experimental and theoretical study of the circular dichroism spectra of oxa- and thia- [2.2] metacyclophane

✍ Scribed by S. Grimme; S.D. Peyerimhoff; S. Bartram; F. Vögtle; A. Breest; J. Hormes

• Publisher: Elsevier Science
• Year: 1993
• Tongue: English
• Weight: 737 KB
• Volume: 213
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(93)85414-j

✦ Synopsis

The excited electronic states of (-)-(M)-1-oxa [ 2.2]metacyclophane and (-) -( M)-1-thia[2.2]metacyclophane are discussed in the light of experimental UV/WV optical absorption and circular dichroism (CD) spectra and multireferencc configuration interaction (MRD-CI) calculations of excitation energies and rotatory strengths. As one-particle basis, semi-empirical AM1 and MNDGC wavefunctions expressed in terms of localized molecular orbit& (LMO) are used. Good agreement between experimental and calculated CD spectra is obtained by correlating only a small portion of the 80 valence electrons of the compounds. The dominant CD transitions of the oxa[ 2.2]metacyclophane can be characterized as separate and coupled XrF transitions localized in the aromatic rings. The CD spectrum of the thia[2.2]metacyclophane is mainly described by valence-type excitations involving the lone-pair orbital of the sulphur atom (3~) and/or anti-bonding o' MOs of C-S bonds; localized xrc' transitions are of lower intensity.