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

摘要

The energy and nucleus-independent chemical shift (NICS) of 95 isomers of N-confused porphyrazine (NCPz), including normal porphyrazine (N _0CPz), N-confused porphyrazine (N_1CPz), doubly N-confused porphyrazine (N_2CPz), triply N-confused porphyrazine (N _3CPz), and fully N-confused porphyrazine (N_4CPz), 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 (N_0CPz-1), +23.481 (N_1CPz-5), +41.849 (N2CPz-a4), +61.738 (N3CPz-b3), and +84.596 (N4CPz-b13), respectively. The most stable isomers of N_2CPz, N_3CPz, and N_4CPz are not necessarily the most aromatic but rather nonaromatic, especially in the case of N _3CPz and N_4CPz. 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 (N_0CPz-1), -14.0458 (N_1CPz-2), -12.8171 (N_2CPz-d1), -11.5961 (N _3CPz-b6), and -12.8012 ppm (N_4CPz-a6), respectively.