Conformational analysis of natural products

Electronegativity acc. Dailey and Shoolery

Group Electronegativities

It has long been recognized that there is a relationship between the electron withdrawing power of substituents and proton chemical shifts. A good correlation was found between the difference in α and β proton chemical shifts in substituted ethanes and electronegativity. Calculated from 1H chemical shift differences between CH2 and CH3 in ethyl derivatives.
Values in column two are calculated using equ. 1 (based on 30 MHz NMR, 1955) and values in column three by equ. 2 (based on 60 MHz NMR, 1961). The electronegativities are taken from Huggins[3].
Whilst a cursory inspection of the derived electronegativities suggest that there is a correlation with the chemical shifts there are a number of inconsistencies. For example the value for the cyano group is lowest of all groups dispite the fact that all chemical data point to a much higher electronegativity.

Equation 1

χ=0.6945*(δCH2 -δCH3 )+1.71

Equation 2

χ=0.684*(δCH2 -δCH3 )+1.78

δCH2 =ppm  δCH3 =ppm
Equ. 1 χ=
Equ. 2 χ=

GroupχHugginsχ Equ. 1χ Equ. 2
Ph 2.602.702.75
CHO 2.602.612.69
COR 2.602.61
COOH 2.602.572.60
CN 2.602.522.49
OH 3.503.513.43
OR 3.503.31
ONO2 3.503.913.90
SH 2.602.45
SR 2.602.642.64
NH2 3.052.992.91
F 3.903.93
Br 2.952.942.96
I 2.652.682.66


  1. B.P. Dailey, J.N. Shoolery; J. Am. Chem. Soc. 77 (1955) 3977-3981.
  2. J. Cavanaugh, B.P. Dailey; J. Phys. Chem. 34 (1961) 1099-1107.