N.M.R. Spectral Studies of Some Quinolone Derivatives. Effect of Substitution on the Degree of Hydrogen Bonding

Abstract
The chemical shift of the NH protons for a series of monomethyl-, dimethyl- and trimethyl- substituted 2- and 4- quinolones has been studied. Compounds with an 8-methyl substituent exhibit a characteristic upfield shift which is considered to be due to a reduction in hydrogen bonding as a result of steric effects. The application of this effect to the identification of alkyl substituted quinolones and some natural products is discussed.