The Energy of the C–H Bond in the Fluoro-Toluenes

Abstract

The pyrolysis of the three fluoro‐toluenes was investigated, and it was shown that the mechanism of the decomposition is the same as suggested previously for the decomposition of toluene and the xylenes. The experimental results prove that the C–H bond energy in all fluoro‐toluenes is nearly the same as the C–H bond energy in toluene, i.e., about 78 kcal./mole, thus showing that the field effect has very little influence on the bond energy. This conclusion definitely establishes the presence of hyperconjugation for para‐xylene as the cause of the weakening of the C–H bond in the CH₃ groups. The difference in the effects of dipoles on ionic and radical reactions is pointed out.