Rate factors for the detritiation of triptycene, 9,10-dihydroanthracene and o-xylene

Abstract

Rate factors for the detritiation of triptycene, 9,10-dihydroanthracene, and o-xylene by anhydrous trifluoroacetic acid at 70° have been obtained as follows: f₁^tript., 51; f₂^tript., 362; f₁^9,10-dihy., 444; f₂^9,10-dihy., 650; f₃^o-xyl., 1335; f₄^o-xyl., 1895. It is shown that for triptycene the reactivity of the 1-position is considerably less, and that of the 2-position slightly greater, than predicted from the xylene and 9,10-dihydroanthracene data. These results are very satisfactorily accounted for by a theory recently advanced to explain the Mills–Nixon effect. In the light of this theory it is considered that transannular stabilisation of the electron-deficient transition states for substitution in triptycene is probably negligible.

Detritiation of o-xylene and 9,10-dihydroanthrancene under the conditions used does not obey the additivity principle; this deviation is explained principally in terms of the variation in charge distribution in the transition state for substitution according to the position of the transition state along the reaction co-ordinate.