Single-Frequency Proton Decoupling in ¹³C N.M.R. Spectra. ¹³C Chemical Shifts and Methyl Substituent Chemical Shifts in Methylquinolines

Abstract

Single-frequency decoupled and fully coupled spectra have been used to assign ¹³C chemical shifts to a number of methyl-substituted quinolines, and the merits of the various decoupling techniques are compared. Ambiguities in assignments of closely similar chemical shifts by the substituent chemical shift (scs) method have been resolved by meta-¹³C-¹H coupling constants. Long-range methyl scs parameters in methylquinolines, and the limitations of the scs method in shift assignments, are discussed.