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

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