NMR MIChI - Discuss Reference compound

[NRayya]

As it can be concluded from IUPAC recommendations, maybe it should be removed or not be mandatory.

[NRayya]

In most cases the reference compound makes no difference to the chemical shifts except for 15N where it is needed (maybe in few other rarely used nuclei). In these cases it needs to be mandatory.
For 1H and 13C it makes no difference.
Maybe best to fill it automatically when possible, provide a short menu dependant on the nucleus for the user to pick from when automated assignment is not possible.