Heteropentalenes aromaticity: A theoretical study

Theoretical calculations at the B3LYP/6-311++G** level including GIAO and NICS chemical shifts have been carried out on seven simple heterocycles (furan, thiophene, pyrrole, 1H-imidazole, 1H-pyrazole, 1H-1,2,3-triazole, 2H-1,2,3-triazole) and 28 heteropentalenes (22 of them being azapentalenes). The relative energies are discussed in function of the heteroatoms and of the topology ([2,3-b] vs. [3,2-b]) for isomers and tautomers. Schleyer's NICS(0) and NICS(1) are used to discuss the aromaticity of these compounds. (c) 2007 Elsevier B.V. All rights reserved.