NMR 11 - Connecting peaks with coupling constants and skewing

Axiom: The coupling constants of a group of protons which split one another must be identical.

The above is extremely useful in interpreting spectra. Example:

Using J values, we can tell that C is coupled to A, and B is coupled to D.

The magnitude of the coupling constant also provides structural clues, such as whether a bond is cis or trans.

"Skewing" is another way which can be used to link multiplets. This is a tendency for the outer lines on a multiplet to lean towards the peak it is coupled with.

An example of skewing can be found in the previously-mentioned ethyl iodide: