A Proton–magnetic–resonance Spectroscopic Investigation of Intramolecular Hydrogen Bonding in 4–Substituted–2–nitrodiphenylamine Disperse Dyes

Detection of long–range coupling constants, JNH, H5, in 100–MHz proton–magnetic–resonance spectra confirms the presence of intramolecular NH ON hydrogen bonding in some 2–nitrodiphenylamine disperse dyes. Measurements in polar and non–polar solvents on 2–nitrodiphenylamine and on twelve 4–substituted derivatives indicate weakening of the bonding, which is related to light fastness, when the 4–substituent is a strong electron acceptor.