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Magnetic circular dichroism of an unaromatic planar [8]annulene
Author(s) -
Wen Jin,
Uto Takayuki,
Chalupský Jakub,
Casher Deborah L.,
Raabe Gerhard,
Fleischhauer Joerg,
Yanai Takeshi,
Tsuji Hayato,
Komatsu Koichi,
Michl Josef
Publication year - 2018
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.3854
Subject(s) - annulene , chemistry , antiaromaticity , magnetic circular dichroism , planar , crystallography , spectral line , density functional theory , circular dichroism , symmetry (geometry) , absorption spectroscopy , stereochemistry , computational chemistry , molecule , aromaticity , quantum mechanics , physics , geometry , computer graphics (images) , organic chemistry , mathematics , computer science
Abstract An overview of magnetic circular dichroism (MCD) spectroscopy of π‐electron systems derived from a 4 N ‐electron perimeter is provided, with emphasis on the hypothetical parent cycloocta‐1,3,5,7‐tetraene of D 8 h symmetry ( 1 ) and its D 4 h symmetry derivatives. UV‐visible absorption and MCD spectra of 2 , a D 4 h symmetric cycloocta‐1,3,5,7‐tetraene planarized by the effect of 4 bicyclo[2.1.1]hexeno units fused to its 8‐membered ring, are reported and interpreted. The perimeter model is applied to obtain an understanding of the nature of electronic states in 1 and 2 and to predict general trends in the spectra. The electronic excitation patterns are found to be different in the antiaromatic D 8 h and unaromatic D 4 h species, and their states cannot be unequivocally correlated. The results of time‐dependent density functional theory and extended multistate complete active space second‐order perturbation theory (XMS‐CASPT2) computations agree with the algebraic perimeter model analysis and reproduce the spectra of 2 well, including three of the four observed MCD signs of A and B terms.