Domene Carmen, Fowler Patrick W, Jenneskens Leonardus W, Steiner Erich
Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, UK.
Chemistry. 2007;13(1):269-76. doi: 10.1002/chem.200600507.
Current-density maps, calculated at the ab initio RHF//6-31G**/CTOCD-DZ level, show no significant pi ring current in planar equilateral geometries of neutral and dianionic [N]radialenes, oxocarbons and thiocarbons C(N)Y(N) (q-) (Y=CH(2), O, S; N=4, 5, 6; q=0 (1 a-12 a), 2 (1 b-12 b)). Only the N=3 deltate dianions C(3)Y(3) (2-) (Y=CH(2), O, S (1 b, 5 b and 9 b)) have discernible pi ring current, and then with at most 20-25 % of the strength of the standard benzene current. On the magnetic criterion, lack of current is definitive evidence against aromaticity. Pictorial molecular-orbital analysis within the ipsocentric approach shows this to be an inevitable consequence of the nodal structure of the pi and pi* orbitals of [N]radialene-like systems. On grounds of angular-momentum symmetry, spatial distribution, or both, the HOMO-LUMO excitation does not contribute a significant central diamagnetic ring current.
在从头算RHF//6 - 31G**/CTOCD - DZ水平计算得到的电流密度图显示，中性和双阴离子型的氮杂并苯、羰基化合物和硫羰基化合物C(N)Y(N)(q - )（Y = CH₂、O、S；N = 4、5、6；q = 0（1a - 12a）、2（1b - 12b））的平面等边几何结构中不存在显著的π环电流。只有N = 3的三角双阴离子C₃Y₃(2 - )（Y = CH₂、O、S（1b、5b和9b））有可分辨的π环电流，且其强度至多为标准苯环电流强度的20 - 25%。根据磁性标准，没有电流是反对芳香性的确凿证据。在同中心方法内的图形分子轨道分析表明，这是氮杂并苯类体系的π和π*轨道节点结构的必然结果。基于角动量对称性、空间分布或两者，HOMO - LUMO激发不会产生显著的中心抗磁环电流。
