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Two types of molecules having axial chirality: allenes (left) and binaryl atropisomers (right) In chemistry, axial chirality is a special case of chirality in which a molecule contains two pairs of chemical groups in a non-planar arrangement about an axis of chirality so that the molecule is not superposable on its mirror image.
These types of chirality are far less common than central chirality. BINOL is a typical example of an axially chiral molecule, while trans-cyclooctene is a commonly cited example of a planar chiral molecule. Finally, helicene possesses helical chirality, which is one type of inherent chirality.
Chirality is also seen in the study of facial asymmetry and is known as aurofacial asymmetry. [35] Schema of the development of the axial twist in vertebrates. According to the Axial Twist theory, vertebrate animals develop into a left-handed chirality. Due to this, the brain is turned around and the heart and bowels are turned by 90°. [36]
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).
Chiral molecules produced within the fields of organic chemistry or inorganic chemistry are racemic unless a chiral reagent was employed in the same reaction. At the fundamental level, polarization rotation in an optically active medium is caused by circular birefringence, and can best be understood in that way.
For example, butane has three conformers relating to its two methyl (CH 3) groups: two gauche conformers, which have the methyls ±60° apart and are enantiomeric, and an anti conformer, where the four carbon centres are coplanar and the substituents are 180° apart (refer to free energy diagram of butane).
Bis(oxazoline) ligands (often abbreviated BOX ligands) are a class of privileged chiral ligands containing two oxazoline rings. They are typically C 2 ‑symmetric and exist in a wide variety of forms; with structures based around CH 2 or pyridine linkers being particularly common (often generalised BOX and PyBOX respectively).