Scalar coupling constants - 3JHH Pachler
Introduction
J-couplings
Chemical shifts
Hydroxy methyl
IntroductionJ-couplingsChemical shiftsHydroxy methyl

3JHH calculation

The magnitude of three-bond 1H-1H coupling constants is determined mainly by the torsion angle between the protons but substituents, especially electronegative ones, do also affect the coupling. They influence the coupling in two ways; they cause a change in overall magnitude of the Karplus equation, and they cause a shift of the maxima and minima of the curve. Several attempts have been made to account for these effects.
This program calculates 3JHH values according to Pachler. Since the equation depends on the relative orientation of the substituents a molecular model will be of help. Turn the model so that the proton on the near side is pointing up then use the schemes below to determine the numbering of the substituents (e.g. S1, S2 etc.) and select the appropriate elements from the menus.

"The Dependence of Vicinal Proton-Proton Coupling Constants on Dihedral Angle and Substituents"
K.G.R. Pachler
J. Chem. Soc., Perkin Trans (1972) 1936-1940

It is also possible to calculate the torsion angles that correspond to a particular J-value. There can be one to four angles depending on the size of the coupling constant. (A "-" means that there is no further solution)

S1 S2 S3 S4
H,H torsion angle → 3JHH
Torsion angles corresponding to the 3JH,H-value:
Delicious Digg reddit Facebook StumbleUpon