Downfield Proton Chemical Shifts Are Not Reliable Aromaticity Indicators

The downfield chem. shifts of arene hydrogens (delta 1H) are due only in part to the pi ring current contribution [sigma.dblvert.(pi)]; local framework effects are equally important. Neither proton chem. shifts nor even sigma.dblvert.(pi) tensor elements, per se, are reliable aromaticity indicators. Unsatd. polycyclic hydrocarbons with nonarom. quinoid structures have delta 1H and sigma.dblvert.(pi) values in the "arom. range". Conversely, numerous arom. protons, including those in five-membered ring heterocycles, resonate in the "nonarom. range". [on SciFinder (R)]


Published in:
Organic Letters, 7, 8, 1457-1460
Year:
2005
Keywords:
Note:
CAN 142:429747 22-2 Physical Organic Chemistry Center for Computational Chemistry, Department of Chemistry,University of Georgia,Athens,GA,USA. Journal 1523-7060 written in English. 85-01-8 (Phenanthrene); 91-20-3 (Naphthalene); 92-24-0 (Naphthacene); 95-13-6 (1H-Indene); 120-12-7 (Anthracene); 253-01-0 (Cyclobuta[1,2:3,4]dicyclopentene); 257-24-9 (Heptalene); 268-37-1 (2H-Benz[f]indene); 270-53-1 (2H-Indene); 275-51-4 (Azulene); 4026-23-7 (Bicyclo[4.2.0]octa-1,3,5,7-tetraene); 850661-43-7; 850661-44-8 Role: PRP (Properties) (downfield NMR proton chem. shifts are not reliable aromaticity indicators)
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 Record created 2007-10-22, last modified 2018-03-17


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