Suprafacial on:
[Wikipedia]
[Google]
[Amazon]
Antarafacial ( Woodward-Hoffmann symbol a) and suprafacial (s) are two 
topological
In mathematics, topology (from the Greek words , and ) is concerned with the properties of a geometric object that are preserved under continuous deformations, such as stretching, twisting, crumpling, and bending; that is, without closing ...
concepts in organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clay ...
describing the relationship between two simultaneous chemical bond
A chemical bond is a lasting attraction between atoms or ions that enables the formation of molecules and crystals. The bond may result from the electrostatic force between oppositely charged ions as in ionic bonds, or through the sharing o ...
making and/or bond breaking processes in or around a reaction center. The reaction center can be a p- or sp''n-''orbital (Woodward-Hoffmann symbol ω), a conjugated system
In theoretical chemistry, a conjugated system is a system of connected p-orbitals with delocalized electrons in a molecule, which in general lowers the overall energy of the molecule and increases stability. It is conventionally represent ...
(π) or even a sigma bond
In chemistry, sigma bonds (σ bonds) are the strongest type of covalent chemical bond. They are formed by head-on overlapping between atomic orbitals. Sigma bonding is most simply defined for diatomic molecules using the language and tools o ...
(σ).
* The relationship is ''antarafacial'' when opposite faces of the π system or isolated orbital are involved in the process (think ''anti''). For a σ bond, it corresponds to involvement of one "interior" lobe and one "exterior" lobe of the bond.
* The relationship is ''suprafacial'' when the same face of the π system or isolated orbital are involved in the process (think ''syn''). For a σ bond, it corresponds to involvement of two "interior" lobes or two "exterior" lobes of the bond.
The components of all pericyclic reactions, including sigmatropic reactions and cycloaddition
In organic chemistry, a cycloaddition is a chemical reaction in which "two or more unsaturated molecules (or parts of the same molecule) combine with the formation of a cyclic adduct in which there is a net reduction of the bond multiplicity". ...
s, and electrocyclizations, can be classified as either suprafacial or antarafacial, and this determines the stereochemistry
Stereochemistry, a subdiscipline of chemistry, involves the study of the relative spatial arrangement of atoms that form the structure of molecules and their manipulation. The study of stereochemistry focuses on the relationships between stereo ...
. In particular, antarafacial topology corresponds to inversion of configuration for the carbon atom of a , ''n''
The comma is a punctuation mark that appears in several variants in different languages. It has the same shape as an apostrophe or single closing quotation mark () in many typefaces, but it differs from them in being placed on the baseline ...
sigmatropic rearrangement, and conrotation for electrocyclic ring closure, while suprafacial corresponds to retention and disrotation.
An example is the ,3hydride shift, in which the interacting frontier orbitals are the allyl
In organic chemistry, an allyl group is a substituent with the structural formula , where R is the rest of the molecule. It consists of a methylene bridge () attached to a vinyl group (). The name is derived from the scientific name for garlic, ...
free radical
A daughter category of ''Ageing'', this category deals only with the biological aspects of ageing.
Ageing
Ailments of unknown cause
Biogerontology
Biological processes
Causes of death
Cellular processes
Gerontology
Life extension
Metabo ...
and the hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
1s orbitals. The suprafacial shift is symmetry-forbidden because orbitals with opposite algebraic signs overlap. The symmetry allowed antarafacial shift would require a strained transition state
In chemistry, the transition state of a chemical reaction is a particular configuration along the reaction coordinate. It is defined as the state corresponding to the highest potential energy along this reaction coordinate. It is often marked ...
and is also unlikely. In contrast a symmetry allowed and suprafacial ,5hydride shift is a common event.F.A. Carey, R.J. Sundberg, ''Advanced Organic Chemistry'' Part A {{ISBN, 0-306-41087-7
References