The long range coupling: COSY

This experiment allows the detection of the correlation peaks caused by weak coupling constant (less than one Hz) and which are not detectable with the COSY 9O° pulse sequence^[1].

For the "long range" COSY sequence, we artificially increase the evolution and detection period by introducing a fixed delay on both side of the mixing time (Fig. 18).

Fig. 18 : The long range COSY

The chosen example is the saccharine molecule (see also Fig 29).

The spectrum 5 is a 90° COSY pulse sequence. The scalar coupling between neighbouring protons G1 and G2 are clearly seen.

The spectrum 6 is a L.R. COSY pulse sequence. The long range couplings appear between the G1 proton and the G3 and G4 protons.

Fig. 29 : Saccharine molecule

Spectrum 5 : 90° COSY

Spectrum 6 : LR COSY