Conrotatory and disrotatory
- Conrotatory and disrotatory
-
In a conrotatory mode of an electrocyclic reaction (a class of organic chemical reactions) the substituents located at the termini of a conjugated double bond system move in the same (clockwise or counter clockwise) direction during ring opening or ring closure. In a disrotatory mode, they move in opposite directions.
A simple arrow-pushing analysis fails to explain the quantitative conversion of trans-cis-trans-2,4,6-octatriene to cis-dimethylcyclohexadiene (top of figure). However, a detailed look at the orbital mechanics behind the process reveals that the orbital symmetry of the octatriene's HOMO requires for the end pi orbitals to move in opposite directions to form the correct symmetry found in the sigma bond.
This stereospecificity is found in thermal rearrangements of all conjugated systems containing 4n + 2 pi electron and is based on preservation of orbital symmetry in the highest occupied molecular orbital. Systems containing 4n pi electrons show the opposite conrotatory mode, as do photoinduced rearrangements of 4n + 2 pi electrons. Photoinduced rearrangements of 4n electron systems follow the disrotatory rule.
The Woodward-Hoffmann rules summarize the above different reactions.
References
- Carey, Francis A.; Sundberg, Richard J.; (1984). Advanced Organic Chemistry Part A Structure and Mechanisms (2nd ed.). New York N.Y.: Plenum Press. ISBN 0-306-41198-9.
- March Jerry; (1985). Advanced Organic Chemistry reactions, mechanisms and structure (3rd ed.). New York: John Wiley & Sons, inc. ISBN 0-471-85472-7
Wikimedia Foundation.
2010.
Look at other dictionaries:
Disrotatory — In a disrotatory mode of an electrocyclic reaction (a class of organic reactions) the substituents located at the termini of a conjugated double bond system move in the opposite (clockwise or counter clockwise) direction during ring opening or… … Wikipedia
Conrotatory — In a conrotatory mode of an electrocyclic reaction (a class of organic chemical reactions) the substituents located at the termini of a conjugated double bond system move in the same (clockwise or counter clockwise) direction during ring opening… … Wikipedia
Electrocyclic reaction — In organic chemistry, an electrocyclic reaction is a type of pericyclic rearrangement reaction where the net result is one pi bond being converted into one sigma bond. These reactions are usually unnamed, being categorized by the following… … Wikipedia
Möbius–Hückel concept — The Möbius Hückel treatment is one of two predicting reaction allowedness versus forbiddeness. The concept is the counterpart of the Woodward Hoffmann approach. The methodology in this treatment utilizes the plus minus sign parity in proceeding… … Wikipedia
Möbius aromaticity — In organic chemistry, Möbius aromaticity is a special type of aromaticity believed to exist in a number of organic molecules. In terms of MO theory these compounds have in common a monocyclic array of molecular orbitals in which there is an odd… … Wikipedia
Cheletropic reaction — Pericyclic Reactions Cheletropic reactions are a type of pericyclic reaction. A pericyclic reaction is one that involves a transition state with a cyclic array of atoms and an associated cyclic array of interacting orbitals. A reorganization of σ … Wikipedia
Woodward–Hoffmann rules — The Woodward–Hoffmann rules devised by Robert Burns Woodward and Roald Hoffmann are a set of rules in organic chemistry predicting the stereochemistry of pericyclic reactions based on orbital symmetry. These include electrocyclic reactions,… … Wikipedia
Diarylethene — In chemistry, diarylethene is the general name of a class of compounds that have aromatic groups bonded to each end of a carbon carbon double bond. The simplest example is stilbene, which has two geometric isomers, E and Z. Under the influence of … Wikipedia
Fenestrane — A fenestrane in organic chemistry is a type of chemical compound with a central quaternary carbon atom which serves as a common vertex for four fused carbocycles [ Fenestranes and the flattening of tetrahedral carbon Bhaskar Rao Venepalli and… … Wikipedia