Empirical ³J_CA-CA coupling constants should to a first approximation only depend on the torsion angle w. In fact, due to the planarity of the peptide bond, this coupling constant has no large variation in magnitude, showing a preferable trans conformation (equivalent to w=179.8 degrees) ( 97JACS6360 ). However, it has been shown that the size of ³J_CA-CA depends on the variation in backbone angle phi and can be used to differentiate netween values of phi typical for alpha and beta structures ( 00JACS6268 ).

In addition, it can be used together with cross-correlation DD(HN)-DD(HACA) rates ( 00JACS12017 )

The observable ³J_CA-CA values fall in the range 2.2 to 1.1 Hz with a mean value of 1.6(+-0.2) Hz

³J_CA-CA are only measured in proteins with favorable 13CA relaxation properties.

3D J-quantitative HN(COCA)CA experiment ( 00JACS6268 )