[Bertran05]

In morpholine the equilibrium of two conformers (chair and boat) are not fast and not slowly, so it means that you can not see a difference in NMR spectrum between axial and equatorials protons.

But if you have amine quaternary, with a substituient like a proton of clorhydrate in Nitrogen of morpholine, then you obtain a spectrum where protons axial and equatorials of methylene are in a difference resonance signal!

It's that true?

[a student]

when you want to see the difference between axial and equatorial protons you should change the speed of that dynamic process sometimes you should make it faster and sometimes for some molecules like cyclohexan you should make it slower.
in this case I think when you introduce a bulky substitiuent on nitrogen of morpholine you have made this ring inversion (dynamic process) slower, so  it seems you must be right