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).
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.
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