hydrogenbond

Hydrogen bond is a non-covalent interaction between a hydrogen atom that is covalently bonded to a highly electronegative donor atom (such as oxygen, nitrogen, or fluorine) and a lone pair on another electronegative acceptor atom. It is weaker than a covalent bond but stronger than most van der Waals forces, and it is highly directional.

Geometrically, a hydrogen bond is represented as X–H...Y, where X–H distance is typically around 1.5 Å and H...Y distance around 2.7 Å, with the angle X–H...Y near 180 degrees for strongest interactions. Energetically, hydrogen bonds range roughly from 4 to 40 kJ/mol, influenced by the atoms involved, the environment, and whether the bond is isolated or part of a network.

Hydrogen bonds are widespread in chemistry and biology. In water they form a dynamic, three-dimensional network that contributes to water’s anomalously high boiling point and solvent properties. They stabilize DNA base pairs (adenine–thymine, guanine–cytosine) and help shape protein secondary structures such as alpha helices and beta sheets, influencing folding and stability.

Hydrogen bonds can be intermolecular or intramolecular and may participate in cooperative networks, leading to nonlinear effects. In some systems, sufficiently strong hydrogen bonds enable proton transfer, producing transient ionic or conductive states in solid acids and aqueous solutions.

Hydrogen bonding is central to solvation, crystallography, molecular recognition, and phase behavior. It provides a framework for understanding structure and reactivity across chemistry, biology, and materials science.