Furuta H, Maeda H, Osuka A
Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
J Org Chem. 2001 Dec 14;66(25):8563-72. doi: 10.1021/jo016051b.
The total electronic energy and nucleus-independent chemical shift (NICS) of 95 isomers of N-confused porphyrin (NCP: normal porphyrin (N(0)CP), singly N-confused porphyrin (N(1)CP), doubly N-confused porphyrin (N(2)CP), triply N-confused porphyrin (N(3)CP), and fully N-confused porphyrin (N(4)CP)) have been calculated by the density functional theory (DFT) method. The stability of NCP decreased by increasing the number of confused pyrrole rings. Namely, the relative energies of the most stable isomers in each confusion level increased in a stepwise manner approximately by +18 kcal/mol: 0 (N(0)CP1), +17.147 (N(1)CP2), +37.461 (N(2)CPb3), +54.031 (N(3)CPd6), and +65.636 kcal/mol (N(4)CPc8). In this order, the mean plane deviation of these isomers increased from 0.000 to 0.123, 0.170, 0.215, and 0.251 A, respectively. The unusual tautomeric forms of pyrrole ring with an sp(3)-carbon were found in the stable forms of N(3)CP and N(4)CP. The NICS values at the mean position of the 24 core atoms were nearly the same for the most aromatic isomers regardless of the confusion level: -15.1280 (N(0)CP1), -13.8493 (N(1)CP2), -13.7267 (N(2)CPd1), -11.7723 (N(3)CPb5), and -13.6224 ppm (N(4)CPa6). The positive correlation between aromaticity and stability was inferred from the plots of NICS and the relative energy of NCP for N(0)CP, N(1)CP, and trans-N(2)CP. On the other hand, the correlation was negative for cis-N(2)CP, N(3)CP, and N(4)CP isomers.
采用密度泛函理论（DFT）方法计算了95种N-杂卟啉异构体（NCP：正常卟啉（N(0)CP）、单N-杂卟啉（N(1)CP）、双N-杂卟啉（N(2)CP）、三N-杂卟啉（N(3)CP）和全N-杂卟啉（N(4)CP））的总电子能量和核独立化学位移（NICS）。随着杂化吡咯环数量的增加，NCP的稳定性降低。也就是说，每个杂化水平下最稳定异构体的相对能量以大约+18 kcal/mol的幅度逐步增加：0（N(0)CP1）、+17.147（N(1)CP2）、+37.461（N(2)CPb3）、+54.031（N(3)CPd6）和+65.636 kcal/mol（N(4)CPc8）。按此顺序，这些异构体的平均平面偏差分别从0.000增加到0.123、0.170、0.215和0.251 Å。在N(3)CP和N(4)CP的稳定形式中发现了具有sp(3)-碳的吡咯环的异常互变异构形式。对于最具芳香性的异构体，无论杂化水平如何，24个核心原子平均位置处的NICS值几乎相同：-15.1280（N(0)CP1）、-13.8493（N(1)CP2）、-13.7267（N(2)CPd1）、-11.7723（N(3)CPb5）和-13.6224 ppm（N(4)CPa6）。从NICS与N(0)CP、N(1)CP和反式-N(2)CP的NCP相对能量的关系图推断出芳香性与稳定性之间存在正相关。另一方面，对于顺式-N(2)CP、N(3)CP和N(4)CP异构体，这种相关性为负。
