THERMOCHEMICAL AND THEORETICAL-STUDIES OF 4-METHYLBIPHENYL, 4,4'-DIMETHYLBIPHENYL, 4,4'-DIMETHYL-2,2'-BIPYRIDINE

The standard (p degrees = 0.1 MPa) molar enthalpies of formation for 4 -methylbiphenyl, 4,4'-dimethylbiphenyl and 4,4'-dimethyl-2,2-'bipyridi ne were derived from the standard molar enthalpies of combustion, in o xygen, at T = 298.15 K, measured by static-bomb combustion calorimetry . The standard molar enthalpies of sublimation, at T = 298.15 K, were measured by Calvet microcalorimetry. Theoretical calculations at the a b initio restricted Hartree-Fock (RHF) level with second-order Moller- Plesset (MP2) perturbation theory correlation corrections and density functional theory (DFT) have been carried out for all these molecules in order to access their stabilitites relative to the non-substituted ones. The theoretical results are in general good agreement with the e xperimental results.