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The handedness of an asymmetric molecule.
(particle physics)
The characteristic of particles of spin ½ ℏ that are allowed to have only one spin state with respect to an axis of quantization parallel to the particle's momentum; if the particle's spin is always parallel to its momentum, it has positive chirality; antiparallel, negative chirality.
The characteristic of an object that cannot be superimposed upon its mirror image.



a concept in chemistry characterizing the property of nonsuperimposability of an object with its mirror image. It was first formulated in 1884 by Lord Kelvin (W. Thomson), but it gained common acceptance only after 1966, when it was introduced into stereochemistry by V. Prelog.

In addition to configuration and conformation, chirality is a basic concept of modern stereochemistry. A distinction is made between centric, axial, and planar chirality, to which chiral elements correspond: center, axis, and plane (see Figure 1). For enantiomorphic crystals and some types of molecules, the consideration of chiral space is worthwhile. A chiral center is a broader

Figure 1. Examples of molecules with different chiral elements: (a) center, (b) axis, (c) plane. A, B, C, and D represent different groupings of atoms.

concept than an asymmetric atom, since molecules exist in which the chiral centers do not coincide with any of their atoms. Planar chirality is characteristic of metallo-organic compounds, for example, π-complexes of olefins and arenes. Chirality is a necessary condition for natural molecular optical activity, since chiral objects exist as pairs of enantiomorphs.

The absence of chirality is indicated by the term “achirality.” Achiral molecules may demonstrate induced optical activity. A molecule is prochiral if it may be converted into a chiral molecule by the replacement of a single atom, for example, the replacement of a hydrogen atom in CH2BrCl by a fluorine atom. When chiral and prochiral fragments are combined in one molecule, the phenomenon of nuclear diastereotopy arises, which is observed in nuclear magnetic resonance spectra. The newest method of determining molecular chirality is based on this effect.


Sokolov, V. I. Novoe v stereokhimii. Moscow, 1975.


References in periodicals archive ?
gas chromatography/mass spectrometry with chiral and achiral stationary
Therefore, nobody predicted the formation of a stable helical vinyl homopolymer from an achiral monomer before our discovery of the one-handed helical PTrMA in 1979.
11] The total number of regions and crossings in a reduced alternating achiral knot is always even.
Ab initio computational investigation of physisorption of molecular hydrogen on achiral single--walled carbon nanotubes, J.
Although ethanol, the "key," is achiral, it has two chiral conformers (gauche) corresponding to the orientation of the methyl group with respect to the O-H bond, and one achiral (trans) conformer (see Figure 2).
He includes special cases such as ionic liquids and the formation of chiral aggregates from achiral building blocks and experimental strategies and reagents researchers can use as he describes aryl-containing carboxylic acids and other carboxylic acid-based reagents; hydroxyl- and thiol-containing reagents; amine-based reagents; organic-based chiral derivatizing and solvating agents; reagents incorporating phosphorus, selenium, boron and silicone atoms; host compounds as chiral NMR discriminating agents; chiral discrimination with metal-based reagents; and chiral NMR discrimination with highly ordered systems.
Part of the Berger SFC (Super Fluid Chromatography) product line, the new system is designed for higher sample throughput for chiral and achiral drug purification applications.
This could have also affected the stereochemical distribution of the products because any phase transfer component to the reduction would have taken place in a more achiral environment.
Conversions over 50% without considerable loss in stereoselectivity hint to the possible formation of an achiral intermediate from the racemic starting ketone and that enantioselection rather than kinetic resolution takes place.
By contrast, competition from natural and achiral synthetic ingredients, magnified by maturing end-use markets, will result in below average growth opportunities.
Acetophenone, which is achiral, is reduced to an optically active alcohol, 1-phenylethanol.
78) D-Cysteine is metabolized by DAO to achiral 3MP, which is a substrate of 3MST for the production of [H.