For a hydrogen atom in a molecule to participate in a hydrogen bond, two main things are necessary beyond just “having a hydrogen”:

  1. The H must be bonded to a highly electronegative atom
    The hydrogen must be covalently bonded to N, O, or F (nitrogen, oxygen, or fluorine).

This creates a strongly polar bond, leaving the H with a significant partial positive charge (δ⁺) that can be attracted to a lone pair on another electronegative atom.

  1. There must be a suitable hydrogen‑bond acceptor nearby
    Another molecule (or part of the same molecule) must present a lone pair on a small, highly electronegative atom , again usually N, O, or F.

This atom acts as the hydrogen‑bond acceptor , and the H interacts electrostatically with that lone pair.

Quick‑reference conditions

Condition| What it means
---|---
H bonded to N, O, or F| The H must be directly attached to one of these electronegative atoms (e.g., in O–H, N–H, or F–H groups). 135
Partial positive H (δ⁺)| The bond must be polar enough that the H carries a noticeable positive charge. 179
Nearby acceptor with lone pair| A second N, O, or F atom with at least one lone pair must be close in space and properly oriented. 357
Favorable geometry| The interaction is strongest when the X–H···Y angle (X and Y = N/O/F) is close to 180° , i.e., roughly linear. 57

In short, the hydrogen atom must be part of a polar X–H bond (X = N, O, F) and must be able to “reach” a lone pair on another N, O, or F in a suitable geometry.