Cross-conjugation
Encyclopedia
Cross-conjugation is a special type of conjugation
in a molecule
, when in a set of three Pi bond
s only two pi-bonds interact with each other by conjugation, the third one is excluded from interaction. In classical terms it means that the strict alternation of single and double bonds—CH=CH–CH=CH–CH-- (i.e., conjugated) is interrupted by two consecutive single bonds at each cross-conjugated point in the cross-conjugated pathway: --CH=CH–C(=CR2)–CH=CH--. Examples of cross-conjugation can be found in molecules such as benzophenone
, divinylketones, p-quinones, dendralenes
and fullerene
. The type of conjugation has an impact on reactivity and molecular electronic transition
s.
Conjugated system
In chemistry, a conjugated system is a system of connected p-orbitals with delocalized electrons in compounds with alternating single and multiple bonds, which in general may lower the overall energy of the molecule and increase stability. Lone pairs, radicals or carbenium ions may be part of the...
in a molecule
Molecule
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...
, when in a set of three Pi bond
Pi bond
In chemistry, pi bonds are covalent chemical bonds where two lobes of one involved atomic orbital overlap two lobes of the other involved atomic orbital...
s only two pi-bonds interact with each other by conjugation, the third one is excluded from interaction. In classical terms it means that the strict alternation of single and double bonds—CH=CH–CH=CH–CH-- (i.e., conjugated) is interrupted by two consecutive single bonds at each cross-conjugated point in the cross-conjugated pathway: --CH=CH–C(=CR2)–CH=CH--. Examples of cross-conjugation can be found in molecules such as benzophenone
Benzophenone
Benzophenone is the organic compound with the formula 2CO, generally abbreviated Ph2CO. Benzophenone is a widely used building block in organic chemistry, being the parent diarylketone.-Uses:...
, divinylketones, p-quinones, dendralenes
Dendralenes
A dendralene is a discrete acyclic cross-conjugated polyene. The simplest dendralene is buta-1,3-diene or [2]dendralene followed by [3]dendralene , [4]dendralene and [5]dendralene and so forth. [2]dendralene is the only one not cross-conjugated.The name dendralene is pulled together from the...
and fullerene
Fullerene
A fullerene is any molecule composed entirely of carbon, in the form of a hollow sphere, ellipsoid, or tube. Spherical fullerenes are also called buckyballs, and they resemble the balls used in association football. Cylindrical ones are called carbon nanotubes or buckytubes...
. The type of conjugation has an impact on reactivity and molecular electronic transition
Molecular electronic transition
Molecular electronic transitions take place when electrons in a molecule are excited from one energy level to a higher energy level. The energy change associated with this transition provides information on the structure of a molecule and determines many molecular properties such as color...
s.