Title: Aromaticity in spin-polarized systems: Can rings be simultaneously alpha aromatic and beta antiaromatic?
Abstract: The partition of the multicenter electron delocalization indices and the nucleus independent chemical shift indices into alpha and beta contributions in open-shell systems has been performed. In general it is shown that a full understanding of aromaticity in these systems cannot be achieved by restricting the calculations to the global properties but by dissecting these properties into α and β terms. The 4n+2- and 4n-aromaticity rules for singlet and triplet annulenes, respectively, reduce to a general aromaticity rule when the α and β terms are studied separately. This new rule allows us to extend the concept of conflicting aromaticities to radical systems that are simultaneously α-aromatic and β-antiaromatic or vice versa. The existence of such systems is demonstrated here by means of multicenter electron delocalization indices and nucleus independent chemical shifts. Finally, the global aromatic/antiaromatic character of these radical systems is estimated by means of aromatic stabilization energy, which is shown to be either slightly positive or slightly negative, thus reflecting the small aromatic/antiaromatic character of these radicals and reinforcing the conclusions obtained with aromaticity indices.
Publication Year: 2008
Publication Date: 2008-10-28
Language: en
Type: article
Indexed In: ['crossref', 'pubmed']
Access and Citation
Cited By Count: 45
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