Structural Factors Affecting the Sign and Magnitude of

Signs of two-bond couplings, unlike one-bond couplings, are not always characteristic of the coupled nuclei. The sign usually depends on some or all of the same factors affecting the magnitudes. 

The ratio (XCH)/ (XC) changes systematically with the position of X in the Periodic Table.  

The sign of X(XY) relative to X(XMY) is dependent on the XMY bond angle, but it is usual for X(XY) and X(XMY) to opposite in sign for most XMY bond angles. 

Oxidation States, Coordination Numbers, and Formal Hybridization of Coupled Nuclei 

Like X, K increases with increasing electronegativity of substituents regardless of sign. Many examples are available for X(PMP), as well as for other pairs of nuclei. AT(XMY) changes by as much as a factor of 2 or 3 upon substitution at either X or Y or both with electronegative groups or atoms. 

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