Theoretical study on the structures and aromaticity of N-confused porphyrazine isomers

Abstract

The energy and nucleus-independent chemical shift (NICS) of 95 isomers of N-confused porphyrazine (NCPz), including normal porphyrazine (N0CPz), N-confused porphyrazine (N1CPz), doubly N-confused porphyrazine (N2CPz), triply N-confused porphyrazine (N3CPz), and fully N-confused porphyrazine (N4CPz), have been calculated by the density-functional theory (DFT) method. The stability of NCPz decreased by increasing the number of confused pyrrole rings and the macrocycle tend to be destabilized stepwise by approximately +21 kcal/mol. The relative energies of the most stable isomers in confusion level are 0 kcal/mol (N0CPz-1), +23.481 (N1CPz-5), +41.849 (N2CPz-a4), +61.738 (N3CPz-b3), and +84.596 (N4CPz-b13), respectively. The most stable isomers of N2CPz, N3CPz, and N4CPz are not necessarily the most aromatic but rather nonaromatic, especially in the case of N3CPz and N4CPz. On the other hand, the magnitude of the aromaticity estimated by NICS for these isomers does not differ largely. The NICS values of the most aromatic isomers are −15.5411 (N0CPz-1), −14.0458 (N1CPz-2), −12.8171 (N2CPz-d1), −11.5961 (N3CPz-b6), and −12.8012 ppm (N4CPz-a6), respectively. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010