Effect of Trifluoromethyl Substitution on C-3 Position in 1H NMR of Quinolones / Coumarins

The structural assignment of differently substituted quinolones / coumarins was reviewed using 1H NMR spectral data. In case of quinolones / coumarins, with varied substitutions at C-4 and different positions of the benzenoid ring, there is a great variation in the 1H NMR value of the proton only attached with C-3. It was observed that when different substitutions (methyl / amino / hydroxy / acetoxy / trifluoromethyl) were carried out at C-4 position, maximum deshielding with the proton attached with C-3 was observed with trifluoromethyl substitution. The observation is same even with the variation in different groups at the benzenoid ring.