A Cycloaddition is a pericyclic reaction in which the net result is loss of two pi bonds and gain of two sigma bonds. In organic chemistry, a pericyclic reaction is a type of reaction where the transition state of molecule has a cyclic geometry, and the reaction progresses in a concerted reactions fashion. ... Electron atomic and molecular orbitals, showing a Pi-bond at the bottom right of the picture In chemistry, pi bonds (π bonds) are bonds with a single nodal plane containing the line segment between the two atoms. ... Electron atomic and molecular orbitals, showing among others the sigma bond of two s-orbitals and a sigma bond of two p-orbitals In chemistry, sigma bonds (σ-bonds) are bonds where there is no nodal plane containing the line segment between the two bonded species. ...

Two major cycloaddition reactions are

• Diels-Alder reaction
• 1,3-dipolar cycloaddition

Cycloadditions are usually described by the backbone size of the participants. This would make the Diels-Alder a [4 + 2]cycloaddition, and the 1,3-dipolar cycloaddition a [3 + 2]cycloaddition. This type of reaction is non-polar addition reaction. The Diels-Alder reaction is an organic chemical reaction (specifically, a cycloaddition) between a conjugated diene and a substituted alkene, commonly termed the dienophile to form a substituted cyclohexene system. ... The 1,3-dipolar cycloaddition is an organic chemical reaction (specifically, a cycloaddition) between a 1,3-dipole and a dipolarophile mostly a substituted alkene to form a substituted five-membered ring. ... The Diels-Alder reaction is an organic chemical reaction (specifically, a cycloaddition) between a conjugated diene and a substituted alkene, commonly termed the dienophile to form a substituted cyclohexene system. ... The 1,3-dipolar cycloaddition is an organic chemical reaction (specifically, a cycloaddition) between a 1,3-dipole and a dipolarophile mostly a substituted alkene to form a substituted five-membered ring. ... An addition reaction, in chemistry, is in its simplest terms a organic reaction where two or more molecules combine to form a larger one. ...

There are related cyclizations such as alkyne trimerization and the Ene reaction. A alkyne trimerisation reaction is a [2+2+2] cyclization reaction where three alkyne molecules react to form a benzene compound. ... Ene reactions are Group transfer reactions between an alkyne or alkene, or similar double bonded species and an allyl-like species. ...

Thermal cycloadditions usually have 4n + 2 pi electrons participating in the starting material. These occur, for reasons of orbital symmetry, in a suprafacial-suprafacial or antarafacial-antarfacial manner (rare). There are a few examples of thermal cycloadditions which have 4n pi electrons; (for example the [2 + 2] cycloaddition), these proceed in a suprafacial-antarafacial sense, such as the dimerisation of ketene, in which the orthogonal set of p orbitals allows the reaction to proceed via a crossed transition state. Ketene is an organic compound with the formula CH2CO. Ketene is very reactive, tending to attach itself to other molecules in the form of an acetyl group. ... In mathematics, orthogonal is synonymous with perpendicular when used as a simple adjective that is not part of any longer phrase with a standard definition. ... Electron configuration is the arrangement of electrons in an atom, molecule or other body. ... // Introduction A collision between reactant molecules may or may not result in a successful reaction. ...

Cycloadditions in which 4n pi electrons participate can also occur as a result of photochemical activation. Here, one component has an electron promoted from the HOMO (pi bonding) to the LUMO (pi antibonding). Orbital symmetry is then such that the reaction can proceed in a suprafacial-suprafacial manner. Photochemistry is the study of the interaction of light and chemicals. ... Look up homo in Wiktionary, the free dictionary Homo can refer to multiple things: The Latin word for man or human The genus Homo (see also hominid) The Greek word for same, usually as prefix in compound words, e. ... HOMO and LUMO are acronyms for Highest Occupied Molecular Orbitals and Lowest Unoccupied Molecular Orbitals respectively. ...

Cycloadditions often have metal-catalyzed and stepwise radical analogs, however these are not strictly speaking pericyclic reactions. In chemistry, radicals (often refered to as free radicals) are atomic or molecular species with unpaired electrons or an otherwise open shell configuration. ...

Some cycloadditions instead of pi bonds operate through strained cyclopropane rings; as these have significant pi character. For example, an analog for the diels-alder reaction is the quadricyclane-DMAD reaction: Molecule structure formula of cyclopropane Cyclopropane is a cycloalkane molecule with the molecular formula C3H6 consisting of three carbon atoms linked to each other to form a ring, with each carbon atom bearing two hydrogen atoms. ...

Image File history File links quadricylcane File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ...