doublebonded

Doublebonded is an adjective used in chemistry to describe a molecule or a part of a molecule in which two atoms are connected by a double bond. A double bond consists of one sigma bond and one pi bond, resulting from the overlap of hybridized orbitals and sharing of two pairs of electrons. The most common double bonds are carbon–carbon (C=C) and carbon–heteroatom (for example C=O, C=N, C=S) bonds. The presence of a double bond influences geometry, reactivity, and physical properties, often imposing planarity on the bonded atoms.

The presence of a double bond typically reduces rotational freedom around the bond axis, leading to geometric isomers. In C=C systems, substituents can occupy different spatial arrangements, described as cis/trans or E/Z isomers. This rigidity also affects chemical reactivity, as the pi bond can participate in reactions that the sigma framework alone cannot.

Bond length and strength vary with the atoms involved and their environment. For example, a typical C=C bond length is about 1.34 angstroms, and its bond energy is around 610 kJ/mol in simple hydrocarbons, though these values differ with substituents and surrounding groups. Double bonds influence properties such as polarity, reactivity, and spectra, contributing to distinctive infrared and ultraviolet features.

Common reactions involve double bonds: electrophilic addition, hydrogenation, halogenation, and polymerization of alkenes, as well as oxidation of carbon–carbon or carbon–heteroatom double bonds. Examples of doublebonded motifs include ethene (ethylene), propene, formaldehyde, and carbonyl-containing compounds, all of which illustrate the central role of the double bond in chemistry.