Pressure Effects on the Rates of Aromatization of Hexamethyl(Dewar benzene) and Dewar Benzene. Volume as a Factor in Crowded Molecules

Article abstract of DOI:10.1021/ja00375a035

The effect of pressure on the rate of aromatization of hexamethyl(Dewar benzene) (1a) has been remeasured, and that of the parent Dewar benzene (1b) has been determined for the first time.The results for the former reaction in bromobenzene at 140 deg C indicate that the activation volume is -(12+/-3) cm³/mol, and that for the latter in pyridine at 42.1 deg C is +(5+/-2) cm³/mol.This difference between the two reactions is attributed to the efficient packing of the methyl groups as they undergo gear engagement on the way to hexamethylbenzene (2a); the overall react tion volume in the reaction of 1a is -22 cm³/mol.This conversion is also subject to an induced side reaction which is held responsible for an earlier overstimate of the volume reduction.