The 3D HNCA-E.COSY (also referred as HNCA-J) experiment allows to measure several J(HN-X) coupling constants (X is the passive spin) in ¹³C,¹⁵N-labeled proteins in H₂O from E.COSY-like multiplet patterns.

Implementation on AVANCE spectrometers equipped with a third channel and pulsed field gradients (PFGs).

Several variants have been proposed as a function of the t₁ and t₂ evolution periods in which the state of the corresponding passive spin has been preserved:

3D HNCA[HA]-E.COSY experiment (( 89JACS5474 , 90JMR183-87 , 90JMR433-90
91JMR436-93 , 91JACS6323 , 93JMRB194-101 , 94JMRB172-104 , 96JACS2483 , 94JB231, 94JB587, 92ANG1609, 93JB239, 92JMR552) to measure J(HN-HA) coupling constants.

3D HNCA[CO]-E.COSY experiment ( 94JMRB172-104 , 95JACS1810 ) to measure J(HN-CO) coupling constants.

3D HNCA[CB]-E.COSY experiment ( 96JACS2483 ) to measure J(HN-CB) coupling constants.

The 3D HNCA-E.COSY experiment affords a 3D map with (F1,F2,F3=CA,N,NH) in which coupling constants are extracted from cross-peaks showing E.COSY patterns in the CA,NH plane