Benzotriptycenes (o-benzenobenzanthracenes). A proton magnetic resonance study

Abstract

¹ H N.m.r. spectra at 100 MHz are reported for five diffrent benzotriptycenes (o-benzenobenzanthracenes)(II)–(VI) and three model compounds, measured in CCl₄ solution. Calculated coupling constants are given, and no transannular resonance or polarization effect between the chromophores is detectable. Experimental τ values for the cage bridgehead protons are compared to those of other reported compounds by means of both the Johnson–Bovey and McWeeny ‘aromatic ring current’ models. The chromophores in (I)–(VI) are evidently under bond angle strain caused by the cage. This causes partial double bond fixation, and reduces the aromatic ring current to about half of that expected in each ring.