Attractive Interactions between Carbonyls and Groups Bearing Lone-pair Electrons in Triptycene Systems

Abstract
Compounds which carry a methoxyl or a chloro group in 1-position and a substituted carbonylmethyl group in 9-position of the triptycene system have been prepared to examine populations of rotamers by 1H NMR spectra. The methoxy compounds favored the ±sc conformations, whereas the ap conformations were relatively favored in the chloro compounds. The results indicate that there are attractive interactions between the carbonyls and a methoxyl or a chloro group and are discussed from the electron-accepting ability of the carbonyl group and the electron-donating ability of the methoxyl and the chloro groups. An aldehyde group was apparently less able to interact with electron-donors than a ketone. This apparent anomaly was discussed from the intramolecular dipolar interactions.

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