Hydrogenbindende

Hydrogenbindende, also known as hydrogen bonding, is a type of non-covalent interaction that occurs when a hydrogen atom covalently attached to a highly electronegative atom forms an attraction to a lone pair on a second electronegative atom. Although it is weaker than a covalent bond, hydrogen binding can strongly influence molecular structure and properties.

Mechanism and geometry: An H-bond donor is typically a N–H or O–H group; the acceptor is a lone pair on N, O, or F. Distances between donor hydrogen and acceptor are generally about 2.7 to 3.5 Å, with near-linear arrangements (D–H...A angle close to 180°) yielding stronger interactions. Energies range roughly from 4 to 40 kJ/mol depending on environment, substituents, and solvent; in water and in biological macromolecules, many hydrogen bonds operate cooperatively.

Roles and significance: Hydrogen bonding shapes the structure and properties of water, alcohols, and carbohydrates; it stabilizes DNA base pairing (A–T with two H-bonds, G–C with three) and contributes to protein secondary structures such as alpha helices and beta sheets. It also governs solubility, boiling and melting points, and the organization of molecular networks in crystals and polymers.

Detection and theory: Hydrogen bonds are inferred from spectroscopic changes, such as red shifts of O–H and N–H stretching vibrations in infrared spectra, and from NMR shifts. They are described in models ranging from simple electrostatic and statistical approaches to quantum mechanical treatments, including density functional theory and specialized models for hydrogen-bond networks.

Limitations and context: Because hydrogen bonds are weaker than covalent bonds, they are sensitive to temperature, solvent, and concentration. Collective networks of hydrogen bonds can produce significant macroscopic effects even when individual bonds are relatively weak.