Scalar coupling constants are sensitive to the geometrical features of a molecule and therefore, their magnitude provides a direct insight into the geometry and electronic structure of a molecule. For example, the Karplus equation [J. Chem. Phys., 30, 11 (1959), J. Am. Chem. Soc., 85, 2870 (1963)] describes the relationship between the 3J coupling constant and the dihedral angle between vicinal hydrogens.
After the pioneering work of Karplus, several other generalized Karplus equations have been proposed for the mutual dependence of J and the dihedral angle. Among these, Haasnoot-de Leeuw-Altona (HLA) are by far the most widely used. Applications including other generalized Karplus equations are scarce which hinder their general use for the common organic chemist. Such is the case of the more recent and precise Díez-Altona-Donders (DAD) equations, developed by Altona’s group.
A few years ago, we developed an easy to use J pocket calculator MestReJ which you can now download directly from the link below and use for free with no strings attached.
Download MestReJ at the Mestrelab Research Chemistry Software Product Page
MestReJ is a very easy little application to work with: it uses a Newman projection of the fragment under observation and a plot of the J values against the torsion angle HCC’H’. It implements the two kinds of generalized Karplus equations developed by the Altona’s group: the classical Haasnoot-de Leeuw-Altona equations and the more recent and precise Díez-Altona-Donders equations. The Colucci-Jungk-Gandour, the Barfield-Smith and the Karplus equations are also implemented in the program. For further information, see this article:
A Graphical Tool for the Prediction of Vicinal Proton-Proton 3JHH Coupling ConstantsNavarro-Vazquez, A.; Cobas, J. C.; Sardina, F. J.; Casanueva, J.; Diez, E.
J. Chem. Inf. Comput. Sci.; 2004; 44(5); 1680-1685. DOI: 10.1021/ci049913t
I hope you will find this application useful in your research