A unified correlation of substituent effects with carbon, proton and fluorine chemical shifts in aromatic and olefinic systems

At the present time no completely satisfactory quantum mechanical calculations exist for carbon, proton or fluorine chemical shifts in various substituted aromatic or olefinic systems. However, the chemical shifts in such systems have been shown to be well correlated by a linear multiple regression analysis with the Swain and Lupton field and resonance para meters ℱ and ℛ, and the semiempirical parameter Q. The utility of Q in testing substituent stereochemistry has been exemplified previously. Here the applications of the complete regression analysis to a wide variety of different systems for the three nuclei are given. The correlation is also shown to apply to selenium in substituted selenophenes. The 13C chemical shifts for a series of ortho substituted toluenes are presented and comparisons made with other ortho disubstituted benzenes.