Reduction potentials of para ‐substituted nitrobenzenes—an infrared, nuclear magnetic resonance, and density functional theory study

Formal reduction potentials, E °′, of a series of 12 para ‐substituted nitrobenzenes (R―C 6 H 4 ―NO 2 , where R═NH(CH 3 ), NH 2 , OCH 3 , CH 3 , H, OCO(CH 3 ), Cl, CF 3 , CO(CH 3 ), CO(H), CN, and NO 2 ) were measured and related to experimental parameters and the calculated descriptors: the lowest unoccupied molecular orbital (LUMO) energy ( E LUMO ), electron affinity (EA), electrophilicity index ( ω ), and relative group electronegativity ( χ R ). Excellent correlation was obtained in the linear relationship between E °′ and both E LUMO ( R 2  > 0.99) and ω , followed by EA, χ R , experimental δ 1 H nuclear magnetic resonance (NMR), infrared asymmetric NO 2 stretching frequency ( ν as ), and lastly, δ 13 C NMR. Calculated E LUMO was found to provide the most convenient theoretical means for predicting experimental E °′ while, together with ω , also giving the highest degree of accuracy. Copyright © 2011 John Wiley & Sons, Ltd.