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The chirality of a molecule that has a helical, propeller, or screw-shaped geometry is called helicity [5] or helical chirality. [6] [7] The screw axis or the D n, or C n principle symmetry axis is considered to be the axis of chirality. Some sources consider helical chirality to be a type of axial chirality, [7] and some do not.
Macroscopic examples of chirality are found in the plant kingdom, the animal kingdom and all other groups of organisms. A simple example is the coiling direction of any climber plant, which can grow to form either a left- or right-handed helix. In anatomy, chirality is found in the imperfect mirror image symmetry of many kinds of animal bodies.
The chiral symmetry transformation can be divided into a component that treats the left-handed and the right-handed parts equally, known as vector symmetry, and a component that actually treats them differently, known as axial symmetry. [2] (cf. Current algebra.) A scalar field model encoding chiral symmetry and its breaking is the chiral model.
Chirality, however, is observer-independent: no matter how one looks at a right-hand screw thread, it remains different from a left-hand screw thread. Therefore, a symmetric object has sinistral and dextral directions arbitrarily defined by the position of the observer, while an asymmetric object that shows chirality may have sinistral and ...
Atropisomers exhibit axial chirality (planar chirality). When the barrier to racemization is high, as illustrated by the BINAP ligands, the phenomenon becomes of practical value in asymmetric synthesis. Methaqualone, the anxiolytic and hypnotic-sedative, is a classical example of a drug molecule that exhibits the phenomenon of atropisomerism. [9]
This chiral diphosphine ligand is widely used in asymmetric synthesis. It consists of a pair of 2-diphenylphosphinonaphthyl groups linked at the 1 and 1′ positions. This C 2-symmetric framework lacks a stereogenic atom, but has axial chirality due to restricted rotation (atropisomerism).
Chirality with hands and two enantiomers of a generic amino acid The direction of current flow and induced magnetic flux follow a "handness" relationship. The term chiral / ˈ k aɪ r əl / describes an object, especially a molecule, which has or produces a non-superposable mirror image of itself.
As examples, in PF 5 the axial P−F bond length is 158 pm and the equatorial is 152 pm, and in PCl 5 the axial and equatorial are 214 and 202 pm respectively. [ 2 ] In the mixed halide PF 3 Cl 2 the chlorines occupy two of the equatorial positions, [ 2 ] indicating that fluorine has a greater apicophilicity or tendency to occupy an axial position.