Here we have to get the atom, in the molecule fentanyl, which will behave as a hydrogen (H) bond acceptor from the donor water molecule.
The -O atom in the molecule will behave as the hydrogen bond acceptor from water.
The H-bond always forms between the proton (here water i.e. H₂O) and the proton acceptor atom in a molecule which is essentially is an electronegative element.
In the fentanyl molecule there are two nitrogen (N) atom and one oxygen (O) atom. We know the electronegativity of oxygen is more than the nitrogen. Thus it is expected that the O atom will be H-bond acceptor in the molecule.
The hydrogen bond with water molecule is shown in the figure.
