Substituent and solvent effects on the UV/vis absorption spectra of 3-<i>N</i>-alkyl-5-carboxy uracils

Abstract

1137-1140Absorption spectra of ten 3-N-alkyl-5-carboxy uracils are recorded in fourteen solvents in the range 200-400 nm. The absorption frequencies of carboxy carbonyl electronic transitions are correlated by dual substituent parameter (DSP) treatment involving both polar (σ*) and steric (Es or vc) substituent constants. The effect of solvent polarity and solvent/solute hydrogen bonding interactions on the absorption spectra are interpreted by means of linear solvation energy relationships (LSER) using a general equation of the form v = vo + sπ* + bβ + aα where π* is a measure of the solvent polarity, β is the scale of the solvent hydrogen bond acceptor basicities and a is the scale of the solvent hydrogen bond donor acidities