Measurement of electrophilic aromatic reactivities via pyrolysis of 1-arylethyl acetates. Part III. The 2-position of biphenylene

Abstract

Rates of pyrolysis of 1-(2-biphenylenyl)ethyl acetate have been determined between 368·3 and 337·9°. The ester eliminates 2·46 ± 0·06 times more quickly than the unsubstituted ester at 625°K, and from the previously determined ρ-factor of –0·63 for the pyrolysis of 1-arylethyl acetates at 625°K a σ⁺-value of 0·625 ± 0·15 for the 2-position of biphenylene is obtained. The 2-position of biphenylene is thus very close in electrophilic reactivity to the 2-position of fluorene in good agreement with previous results for electrophilic aromatic hydrogen-exchange. It is shown how the large difference in the reactivity of the 1- and 2-positions of biphenylene (which is greater than calculations predict), can be explained in terms of a theory recently advanced to account for the Mills–Nixon effect.