What is the preferred (strongest) geometry for a classical hydrogen bond?
Note,
D- Donor
H - Hydrogen Atom
A- Acceptor
D–H⋯A angle ≈ 90° (sharp bend)
D–H⋯A angle ≈ 120°
D–H⋯A angle ≈ 160–180° (nearly linear)
No preferred angle – it can be any direction