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Is Free Cyclooctatetraene Dianion an Aromatic System? A Quantum Chemistry Study
Author(s) -
Cao Tingting,
Ma Yipei,
Yan Xiuhua,
Cheng Jiagao,
Luo Youhua,
He Liming,
Zhu Weiliang
Publication year - 2009
Publication title -
chinese journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.28
H-Index - 41
eISSN - 1614-7065
pISSN - 1001-604X
DOI - 10.1002/cjoc.200990321
Subject(s) - chemistry , cyclooctatetraene , aromaticity , delocalized electron , ring (chemistry) , computational chemistry , planar , bond order , electron delocalization , quantum chemistry , quantum chemical , bond length , crystallography , molecular physics , molecule , crystal structure , organic chemistry , supramolecular chemistry , computer graphics (images) , computer science
To investigate whether free cyclooctatetraene dianion (COT 2− ) is aromatic, quantum chemistry methods were used to optimize its structure. Based on the optimized structures, the natural population analysis (NPA) charge, bond order, delocalization energy, nucleus‐independent chemical shift (NICS), and harmonic oscillator model of aromaticity (HOMA) values were computed by DFT‐B3LYP method with basis set 6‐311++G**, which shows that COT 2− is not aromatic as it is not planar and has different bond lengths and bond orders, smallest delocalization energy and positive NICS values. To further confirm the finding, the changes of NICS and energy against ring distortion angle were scanned. The COT 2− has positive NICS values all along the angle from 180° to 120° while other aromatic systems always have negative values. The energy scanning suggests that COT 2− should have the weakest capability to maintain its planar structure. All the calculations strongly indicate that COT 2− is not aromatic. This study also suggests that NICS scan might be a good approach to judge aromaticity.