A push-pull olefin is a type of

olefin In organic chemistry, an alkene, or olefin, is a hydrocarbon containing a carbon–carbon double bond. The double bond may be internal or at the terminal position. Terminal alkenes are also known as α-olefins. The International Union of Pu ...

characterized by an

electron-withdrawing An electron-withdrawing group (EWG) is a group or atom that has the ability to draw electron density toward itself and away from other adjacent atoms. This electron density transfer is often achieved by resonance or inductive effects. Electron-with ...

substituent In organic chemistry, a substituent is one or a group of atoms that replaces (one or more) atoms, thereby becoming a moiety in the resultant (new) molecule. The suffix ''-yl'' is used when naming organic compounds that contain a single bond r ...

on one side of the

double bond In chemistry, a double bond is a covalent bond between two atoms involving four bonding electrons as opposed to two in a single bond. Double bonds occur most commonly between two carbon atoms, for example in alkenes. Many double bonds exist betw ...

and an electron-donating substituent on the other side. This makes the

pi bond In chemistry, pi bonds (π bonds) are covalent chemical bonds, in each of which two lobes of an orbital on one atom overlap with two lobes of an orbital on another atom, and in which this overlap occurs laterally. Each of these atomic orbital ...

very polarized. The rotational barrier for a push-pull olefin is lower than that of an ordinary

and this makes it an interesting candidate for a

molecular switch A molecular switch is a molecule that can be switched between two or more stable or Metastability, metastable states with the use of any external (exogenous) or internal (endogenous) stimuli, such as changes in pH, light, temperature, an electri ...

, for instance

azobenzene Azobenzene is a photoswitchable chemical compound composed of two phenyl rings linked by a azo compound, N=N double bond. It is the simplest example of an aryl azo compound. The term 'azobenzene' or simply 'azo' is often used to refer to a wide c ...

s. A push-pull configuration also helps to stabilize the double bond because the carbon-carbon bond has considerably less double bond character. For instance,

cyclobutadiene Cyclobutadiene is an organic compound with the formula . It is very reactive owing to its tendency to dimerize. Although the parent compound has not been isolated, some substituted derivatives are robust and a single molecule of cyclobutadiene is ...

is a very unstable molecule but with both olefinic bonds in push-pull configuration (two

ester In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...

substituents and two

tertiary amine In chemistry, amines (, ) are organic compounds that contain carbon-nitrogen bonds. Amines are formed when one or more hydrogen atoms in ammonia are replaced by alkyl or aryl groups. The nitrogen atom in an amine possesses a lone pair of elec ...

substituents) the molecule is stable indeed.

References

* ''Ethyl (2-cyano-3-ethoxyacryloyl)carbamate: irreversible thermal isomerization of a push-pull olefin'' Kuangsen Sung, Ming-Chi Lin, Pin-Mei Huang, Bo-Ren Zhuang, Robert Sung,Ru-Rong Wu

Arkivoc ''Arkivoc'' (''Archive for Organic Chemistry'') is a peer-reviewed open access scientific journal covering all aspects of organic chemistry. It is published by the non-profit organization Arkat USA, which was established in 2000 through a personal ...

2005 p. 13

open access (publishing), open access publication

References

See also