Chirality


Also found in: Dictionary, Thesaurus, Medical, Wikipedia.

chirality

[kī′ral·əd·ē]
(chemistry)
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.
(physics)
The characteristic of an object that cannot be superimposed upon its mirror image.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Chirality

 

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.

REFERENCE

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

V. I. SOKOLOV

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
While using sophisticated scanning transmission electron microscopy at Berkeley Lab's Molecular Foundry and at the Cornell Center for Materials Research, David Muller of Cornell University took atomic snapshots of skyrmions' chirality at room temperature in real time.
Rath, Induction and Rationalization of Supramolecular Chirality in The Tweezer-Diamine Complexes: Insights from Experimental and DFT Studies, Inorg.
'Therefore, a symmetrical object has sinistral and dextral directions arbitrarily defined by positions of the observer while an object that has chirality can have sinistral and dextral directions defined by characteristics of the object no matter the position of the observer.
The properties of the refilled material are similar to RCLC-green, except for the opposite chirality. In the reflection mode, the diffraction efficiency of the RCP green light is smaller than that of the LCP green light (g = 0.74), as shown in Figure 3(c).
Figure 2 shows the incoherent bistatic coefficients for different values of chirality parameter.
Nevertheless, it is necessary to mention that they characterized a single layer of a two-dimensional structure (see Figure 1): though chirality may be defined in a plane geometry [11, 12], a planar structure cannot be chiral in the 3D space.
Diameter is the main parameter that affects the on current proportionally in a CNFET apart from barrier height at the S/D contact (or RS/D), chirality, and oxide thickness, but for larger diameters, current tends to saturate due to large screening and scattering effects [14, 24, 25, 33].
We demonstrate the potential for inherent cellular chirality to play an important role in the establishment of organ LR asymmetry.
Previously it has been shown that the chirality can be manipulated by applying magnetic fields to complicated nanowire geometries, but the use of magnetic fields is wasteful of energy and limits the ability to address individual domain walls selectively.
Bertozzi, "Progress and challenges for the bottom-up synthesis of carbon nanotubes with discrete chirality," Chemical Physics Letters, vol.
The negative refractive index can be reached by either increasing the chirality parameter or operating near the electric and/or magnetic resonance frequency zones, where the value of [square root of [[mu].sub.r][[epsilon].sub.r]] becomes smaller than the chirality parameter value [epsilon], which becomes strong around the resonance frequencies, as reported in [10,11].
As the spin(6) Lorentz algebra has two irreducible spinor representations, there are accordingly two kinds of the 't Hooft symbols depending on the chirality of irreducible spin(6) representations.