Folded Conformations. IV. Intramolecular Shielding and Intramolecular Charge-Transfer Interaction in Benzyl Phenyl Sulfones and Sulfoxides

Abstract

Proton magnetic resonance spectra of the title compounds (A-SO2CHR-D) were measured and compared with the spectra of appropriate reference systems containing an alkyl substituent instead of one of the aromatic rings. The observed upfield shifts of the aromatic proton resonances in the title compounds suggest that there is a significant population of folded conformations, which possess a gauche orientation of the aromatic rings. This conclusion is supported by the observation of an intramolecular charge-transfer band in the u.v. spectra of the compounds containing an A ring of high electron affinity and a D ring of low ionization potential. Stabilization of the folded forms may be obtained through minimizing the n–π repulsive forces between the sulfonyl oxygen lone pairs and the π-electron system of the D ring.