A hydrogen bond is a specific type of molecular interaction where a hydrogen atom covalently bonded to a highly electronegative atom (such as nitrogen, oxygen, or fluorine) interacts with another electronegative atom that has a lone pair of electrons. This interaction is stronger than ordinary dipole- dipole forces but weaker than covalent or ionic bonds. It arises not just from electrostatic attraction but also involves partial covalent character due to charge transfer and orbital overlap, making it a resonance-assisted interaction rather than a purely electrostatic force

. Hydrogen bonds can occur between different molecules (intermolecular) or within the same molecule (intramolecular). The general notation is Dn−H···Ac, where Dn is the donor atom covalently bonded to hydrogen, and Ac is the acceptor atom with a lone pair. The hydrogen bond is represented by a dotted line indicating this non-covalent interaction

. This bonding plays a crucial role in many chemical and biological processes. For example, it stabilizes the double helix structure of DNA through hydrogen bonds between nucleotide bases and helps maintain protein folding. It also explains water's unusually high boiling point and its ability to act as a solvent

. In summary, a hydrogen bond is a directional, attractive interaction involving a hydrogen atom bonded to an electronegative donor atom and an electronegative acceptor atom with a lone electron pair, essential for molecular structure and function in chemistry and biology.