Thermochemical and theoretical study of bipyridines

The following standard molar enthalpies of formation in the gaseous state at 298.15 K were determined from the enthalpies of combustion of the crystalline solids and the respective enthalpies of sublimation: 2,2’-bipyridine, 267.9 f 3.0 kJ mol-’; 2,4’-bipyridine, 284.2 f 2.7 kJ mol-’; 4,4‘- bipyridine, 293.1 f 3.6 kJ mol-’. Ab initio geometry optimizations of these molecules at the 3-21G level suggest that those with at least one ortho nitrogen atom assume near planar conformations preferentially, while the others have nonplanar most stable forms. PBIC/C/CEN/1019/92