kaksoissidosta

Kaksoissidosta (Finnish for "double bond") refers to a type of covalent bond between two atoms in which four electrons are shared, commonly represented by an equals sign (e.g., C=C). Structurally, a double bond consists of one sigma bond formed by end-to-end overlap of orbitals and one pi bond formed by side-by-side overlap of p orbitals. This bonding arrangement shortens and strengthens the connection between the bonded atoms relative to a single bond, while being weaker than a triple bond.

Double bonds impose geometric constraints: atoms directly bonded to the doubly linked atoms typically adopt trigonal planar geometry and rotation about the bond axis is restricted. This restriction can give rise to geometric (cis–trans or E–Z) isomerism in suitable molecules. When double bonds alternate with single bonds, conjugation can occur, leading to electron delocalization that affects stability, reactivity and optical properties.

Chemically, double bonds are more reactive than single bonds and commonly undergo addition reactions such as hydrogenation, halogenation, hydrohalogenation and hydration. They are central in many organic transformations and industrial processes, including polymerization of alkenes. Spectroscopic signatures include characteristic infrared absorptions (C=C stretching near 1650 cm−1) and influences on NMR chemical shifts and UV–visible absorption for conjugated systems.

Double bonds are important in biological molecules (for example, unsaturated fatty acids), materials science and organic synthesis. The term in Finnish usage aligns with the general chemical concept of a double bond.