Hydrogen bond
A partial-covalent molecular interaction between a protic hydrogen and an electronegative acceptor.
A hydrogen bond (H-bond) is a specific type of molecular interaction that exhibits partial covalent character and cannot be described as a purely electrostatic force. It occurs when a hydrogen atom, covalently bonded to a more electronegative donor atom or group, interacts with another electronegative atom bearing a lone pair of electrons—the hydrogen bond acceptor. Hydrogen bonding plays a fundamental role in chemistry, biology, and materials science, being responsible for the anomalously high boiling point of water, the stabilization of protein and nucleic acid structures, and key properties of materials like paper, wool, and hydrogels.
- type
- Molecular interaction
- typical_donor_atoms
- Nitrogen (N), oxygen (O), fluorine (F)
- typical_acceptor_atoms
- Nitrogen (N), oxygen (O)
- IUPAC_recommended_notation
- Dn−H···Ac
Lore & Background
Hydrogen bonds arise from a combination of electrostatics, covalency (charge transfer by orbital overlap), and dispersion forces. The general notation is Dn−H···Ac, where the solid line represents a polar covalent bond and the three dots indicate the hydrogen bond. Hydrogen bond donors have a protic hydrogen attached to an electronegative atom such as nitrogen, oxygen, or fluorine, while acceptors have a lone pair of electrons, such as the nitrogen atom of amines and amides and the oxygen atom of carboxylates and water. The term 'hydrogen bond' is generally used for well-defined, localized interactions with significant charge transfer and orbital overlap, such as those in DNA base pairing or ice, whereas 'hydrogen-bonding interactions' is a broader term used when the interaction is weaker, more dynamic, or delocalized, such as in liquid water or supramolecular assemblies.
Reader's Guide
Hydrogen bonding is of persistent theoretical interest and spans a continuum from weak van der Waals-like interactions to nearly covalent bonding. This places hydrogen bonds stronger than van der Waals interactions but generally weaker than covalent or ionic bonds. In biological systems, hydrogen bonds mediate molecular recognition, enzyme catalysis, and DNA replication, while in materials science, they contribute to self-assembly, adhesion, and supramolecular organization. The distinction between 'hydrogen bond' and 'hydrogen-bonding interactions' is particularly relevant in structural biology, materials science, and computational chemistry. Spectroscopically, strong hydrogen bonds are revealed by downfield shifts in 1H NMR and shifts of X−H stretching frequency to lower energy in the IR spectrum. The dynamics of hydrogen bond structures in water can be probed by OH stretching vibration, and in protic organic ionic plastic crystals, variable-temperature infrared spectroscopy can reveal the temperature dependence of hydrogen bonds.
Did You Know?
- Hydrogen bonds involving C−H bonds are both very rare and weak.
- The resonance assisted hydrogen bond (RAHB) is characterized by π-delocalization involving the hydrogen atom and cannot be properly described by the electrostatic model alone.
Frequently Asked Questions
Who is Hydrogen bond?
Hydrogen bond is a partial-covalent molecular interaction that forms when a hydrogen atom, already covalently attached to an electronegative donor such as oxygen, nitrogen, or fluorine, reaches toward another electronegative atom bearing a lone pair. It is not merely an electrostatic attraction but a distinct intermolecular force with measurable covalent character.
How does Hydrogen bond's story end?
Hydrogen bond has no fixed ending; it is a transient, continuously forming and breaking interaction that persists only while donor and acceptor remain in proximity. In liquid water, each individual bond typically lasts just a few picoseconds before a new partner takes its place.
Why is Hydrogen bond so important?
Without Hydrogen bond, water would boil far below its familiar 100 °C, proteins would fail to fold, and the base-pairing that encodes genetic information would collapse. It is arguably the single most consequential weak interaction across chemistry, biology, and materials science.
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