How to select amide hydrogen in a cyclic peptide nanotube in index file?

GROMACS version:
GROMACS modification: Yes/No
Hello, I want to select the amide hydrogen group in my index file as I want to calculate the hbond between them and water molecules. When I use HN it does select atoms, but I see no hbond while in articles they say that it happens! Then probably the index file and selection have a problem. thanks