Studies on the Nuclear Magnetic Resonance Spectra in Aliphatic Systems. I. Preliminary Discussions on the Chemical Shifts of Alkyl Derivatives

Abstract

Proton chemical shifts in alkyl-R compounds are examined with respect to substituent constants and following results are obtained. 1) α-¹H chemical shifts are linear with σ_i-0.25 σ_π except for nitro group of isopropyl-R series, CN and halogen group. 2) β-¹H chemical shifts are linear with σ_i. These results indicate that 20% π-electronic together with 80% σ-electronic effect takes part in determining α-¹H chemical shifts, on the other hand β-¹H chemical shifts are dependent mainly on σ-electronic effect. The deviations observed for halogen and cyano groups indicate that induced current effects on α-¹H are diamagnetic in character. The effective shielding constants and substituent electronegativities are also linear with σ_i-0.25σ_π.