Ab initio study of isopyridines

Ab initio calculations at HF/3-21G, HF/6-31G*, HF/6-311++G** and B3LYP/6-31 G* levels of theory for geometry optimization and MP2/6-31G*//HF/6-31G* for a single point total energy calculation are reported for 13 isopyridines 5 -17. Isomers 5-9 with an allenic moiety, are calculated to be 10-40 kcal mo l-l more stable than structures 10-15 with an acetylenic group. The calcula ted energy difference (63.5 kcal mol(-1)) between pyridine and the most sta ble isopyridine (1-aza-2,3,5-cyclohexatriene, 6) is smaller than the differ ence (83.6 kcal mol(-1)) between benzene and the most stable isobenzene 3. (C) 2001 Elsevier Science B.V. All rights reserved.