Factors that Influence J Preliminary Considerations

Theoretical chemists have a relatively complete understanding of the factors that control the sign and magnitude of 7. In fact, they have derived some impressive equations that describe the spin-coupling interaction. We will try our best to steer clear of the high-powered math and take a more qualitative approach. 

Although this model is somewhat naive, it does help us rationalize why one- and three-bond H-H, C-H, and C-C coupling constants are usually positive, while two-bond coupling constants are usually negative. 

So much for the sign of 7. In general, the magnitude (absolute value) of a coupling constant between nuclei a and b (17ab I) is determined by the generalized equation. 

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