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

Group	χHuggins	χ Equ. 1	χ Equ. 2
Ph	2.60	2.70	2.75
CHO	2.60	2.61	2.69
COR	2.60	2.61
COOH	2.60	2.57	2.60
CN	2.60	2.52	2.49
OH	3.50	3.51	3.43
OR	3.50		3.31
ONO₂	3.50	3.91	3.90
SH	2.60	2.45
SR	2.60	2.64	2.64
NH₂	3.05	2.99	2.91
F	3.90	3.93
Cl	3.15	3.19	3.25
Br	2.95	2.94	2.96
I	2.65	2.68	2.66

References

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