Aromatic reactivity. Part XLVII. Effects of 10-substituents on the rates of detritiation at the 9-position of phenanthrene

Abstract

The rates of detritiation of some 10-X-[9-³H]phenanthrenes in anhydrous trifluoroacetic acid have been measured at several temperatures. The values of the rates, k_rel, at 70° relative to that for [9-³H]phenanthrene are (X =) Me, 180; F, 4·1; Cl, 0·185; Br, 0·11; I, 0·14. Change of temperature has a large effect on the activating influence of the methyl group, the values of k_rel being ∼420, ∼350, and 230 at 0, 25, and 50°, respectively. The relatively large activation by fluorine, and the order of deactivation by the other halogens point to a contribution from resonance effects relative to those from inductive effects which is unusually high for ortho-substituents.