Chirality /kaɪˈrælɪtiː/ is a property of asymmetry important in
several branches of science. The word chirality is derived from the
Greek χειρ (kheir), "hand," a familiar chiral object.
An object or a system is chiral if it is distinguishable from its
mirror image; that is, it cannot be superposed onto it. Conversely, a
mirror image of an achiral object, such as a sphere, cannot be
distinguished from the object. A chiral object and its mirror image
are called enantiomorphs (Greek, "opposite forms") or, when referring
to molecules, enantiomers. A non-chiral object is called achiral
(sometimes also amphichiral) and can be superposed on its mirror
image. If the object is non-chiral and is imagined as being colored
blue and its mirror image is imagined as colored yellow, then by a
series of rotations and translations the two can be superposed,
producing green, with none of the original colors remaining.
The term was first used by Lord Kelvin in 1893 in the second Robert
Boyle Lecture at the
Oxford University Junior Scientific Club which
was published in 1894:
I call any geometrical figure, or group of points, 'chiral', and say
that it has chirality if its image in a plane mirror, ideally
realized, cannot be brought to coincide with itself.
Human hands are perhaps the most universally recognized example of
chirality. The left hand is a non-superimposable mirror image of the
right hand; no matter how the two hands are oriented, it is impossible
for all the major features of both hands to coincide across all
axes. This difference in symmetry becomes obvious if someone
attempts to shake the right hand of a person using their left hand, or
if a left-handed glove is placed on a right hand. In mathematics,
chirality is the property of a figure that is not identical to its
1.2 Knot theory
5 See also
7 External links
An achiral 3D object without central symmetry or a plane of symmetry
A table of all prime knots with seven crossings or fewer (not
including mirror images).
In mathematics, a figure is chiral (and said to have chirality) if it
cannot be mapped to its mirror image by rotations and translations
alone. For example, a right shoe is different from a left shoe, and
clockwise is different from anticlockwise. See  for a full
A chiral object and its mirror image are said to be enantiomorphs. The
word enantiomorph stems from the Greek ἐναντίος (enantios)
'opposite' + μορφή (morphe) 'form'. A non-chiral figure is called
achiral or amphichiral.
The helix (and by extension a spun string, a screw, a propeller, etc.)
Möbius strip are chiral two-dimensional objects in
three-dimensional ambient space. The J, L, S and Z-shaped tetrominoes
of the popular video game
Tetris also exhibit chirality, but only in a
Many other familiar objects exhibit the same chiral symmetry of the
human body, such as gloves, glasses (where two lenses differ in
prescription), and shoes. A similar notion of chirality is considered
in knot theory, as explained below.
Some chiral three-dimensional objects, such as the helix, can be
assigned a right or left handedness, according to the right-hand rule.
In geometry a figure is achiral if and only if its symmetry group
contains at least one orientation-reversing isometry. In two
dimensions, every figure that possesses an axis of symmetry is
achiral, and it can be shown that every bounded achiral figure must
have an axis of symmetry. In three dimensions, every figure that
possesses a plane of symmetry or a center of symmetry is achiral.
There are, however, achiral figures lacking both plane and center of
symmetry. In terms of point groups, all chiral figures lack an
improper axis of rotation (Sn). This means that they cannot contain a
center of inversion (i) or a mirror plane (σ). Only figures with a
point group designation of C1, Cn, Dn, T, O, or I can be chiral.
A knot is called achiral if it can be continuously deformed into its
mirror image, otherwise it is called chiral. For example, the unknot
and the figure-eight knot are achiral, whereas the trefoil knot is
Animation of left-handed (anticlockwise), circularly polarized, light
as viewed in the direction of the source, in agreement with physics
and astronomy conventions.
In physics, chirality may be found in the spin of a particle, where
the handedness of the object is determined by the direction in which
the particle spins. Not to be confused with helicity, which is the
projection of the spin along the linear momentum of a subatomic
particle, chirality is a purely quantum mechanical phenomenon like
spin. Although both can have left-handed or right-handed properties,
only in the massless case do they have a simple relation. In
particular for a massless particle the helicity is the same as the
chirality while for an antiparticle they have opposite sign.
The handedness in both chirality and helicity relate to the rotation
of a particle while it proceeds in linear motion with reference to the
human hands. The thumb of the hand points towards the direction of
linear motion whilst the fingers curl into the palm, representing the
direction of rotation of the particle (i.e. clockwise and
counterclockwise). Depending on the linear and rotational motion, the
particle can either be defined by left-handedness (ex. translating
leftwards and rotating counterclockwise) or right-handedness (ex.
translating in the right direction and rotating clockwise). A
symmetry transformation between the two is called parity. Invariance
under parity by a
Dirac fermion is called chiral symmetry.
Electromagnetic wave propagation as handedness is wave polarization
and described in terms of helicity (occurs as a helix). Polarization
of an electromagnetic wave is the property that describes the
orientation, i.e., the time-varying, direction (vector), and amplitude
of the electric field vector. For a depiction, see the adjacent image.
(S)-Alanine (left) and (R)-alanine (right) in zwitterionic form at
A chiral molecule is a type of molecule that has a non-superposable
mirror image. The feature that is most often the cause of chirality in
molecules is the presence of an asymmetric carbon atom.
The term chiral in general is used to describe the object that is
non-superposable on its mirror image.
In chemistry, chirality usually refers to molecules. Two mirror images
of a chiral molecule are called enantiomers or optical isomers. Pairs
of enantiomers are often designated as "right-", "left-handed" or if
it has no bias achiral. As polarized light passes through a chiral
molecule, the plane of polarization, when viewed along the axis toward
the source, will be rotated in a clockwise (to the right) or
anticlockwise (to the left). A right handed rotation is dextrorotary
(d); that to the left is levorotary (l). The d- and l-isomers are the
same compound but are called enantiomers. An equimolar mixture of the
two optical isomers will produce no net rotation of polarized light as
it passes through. Left handed molecules have l- prefixed to their
names; d- is prefixed to right handed molecules.
Molecular chirality is of interest because of its application to
stereochemistry in inorganic chemistry, organic chemistry, physical
chemistry, biochemistry, and supramolecular chemistry.
More recent developments in chiral chemistry include the development
of chiral inorganic nanoparticles that may have the similar
tetrahedral geometry as chiral centers associated with sp3 carbon
atoms traditionally associated with chiral compounds, but at larger
scale. Helical and other symmetries of chiral nanomaterials
were also obtained.
All of the known life-forms show specific chiral properties in
chemical structures as well as macroscopic anatomy, development and
behavior. In any specific organism or evolutionarily related set
thereof, individual compounds, organs, or behavior are found in the
same single enantiomorphic form. Deviation (having the opposite form)
could be found in a small number of chemical compounds, or certain
organ or behavior but that variation strictly depends upon the genetic
make up of the organism. From chemical level (molecular scale),
biological systems show extreme stereospecificity in synthesis,
uptake, sensing, metabolic processing. A living system usually deals
with two enantiomers of same compound in a drastically different way.
In biology, homochirality is a common property of amino acids and
carbohydrates. The chiral protein-making amino acids, which are
translated through the ribosome from genetic coding, occur in the L
form. However, D-amino acids are also found in nature. The
monosaccharides (carbohydrate-units) are commonly found in
D-configuration. DNA double helix is chiral (as any kind of helix is
chiral), and B-form of DNA shows a right-handed turn.
R-(+)-Limonene found in orange
S-(–)-Limonene found in lemon
Sometimes, when two enantiomers of a compound found in organisms, they
significantly differ in their taste, smell and other biological
actions. For example, (+)-Limonene found in orange (causing its
smell), and (–)-Limonene found in Lemons (causing its smell), show
different smells due to different biochemical interactions at
human nose. (+)-Carvone is responsible for the smell of
oil whereas (–)-carvone is responsible for smell of Spearmint
S-(+)-Carvone occurs in
Caraway seed oil, and R-(-)-Carvone occurs in
Dextropropoxyphene or Darvon, a painkiller
Levopropoxyphene or Novrad, an anticough agent
Also, for artificial compounds, including medicines, in case of chiral
drugs, the two enantiomers show remarkable difference in effect of
their biological actions. Darvon (Dextropropoxyphene) is a painkiller,
whereas its enantiomer, Novrad (Levopropoxyphene) is an anti-cough
agent. In case of Penicillamine, the S-isomer used in treatment of
primary chronic arthritis, Whereas the R-isomer has no therapeutic
effect as well as being highly toxic.
A natural left-handed helix, made by a certain climber plant's
Macroscopic example of
Chirality is found in plant kingdom, animal
kingdom and all other groups of organism. A simple example is the
coiling direction of any climber plants. It may be one of two possible
type of helix.
Shells of two different species of sea snail: on the left is the
normally sinistral (left-handed) shell of Neptunea angulata, on the
right is the normally dextral (right-handed) shell of Neptunea
In anatomy, chirality is found in the imperfect mirror image symmetry
of many kinds of animal bodies. Organisms such as gastropods exhibit
chirality in their coiled shells, resulting in an asymmetrical
appearance. Over 90% of gastropod species  have dextral
(right-handed) shells in their coiling, but a small minority of
species and genera are virtually always sinistral (left-handed). A
very few species (for example Amphidromus perversus) show an equal
mixture of dextral and sinistral individuals.
In humans, chirality (also referred to as handedness or laterality) is
an attribute of humans defined by their unequal distribution of fine
motor skill between the left and right hands. An individual who is
more dexterous with the right hand is called right-handed, and one who
is more skilled with the left is said to be left-handed.
also seen in the study of facial asymmetry.
In flatfish, the
Summer flounder or fluke are left-eyed, while halibut
Sinistral and dextral
^ Sir William Thomson Lord Kelvin (1894). "The Molecular Tactics of a
Crystal". Clarendon Press.
^ Georges Henry Wagnière, On
Chirality and the Universal Asymmetry:
Reflections on Image and Mirror Image (2007).
^ Petitjean, M. (2017). "
Chirality in metric spaces. In memoriam
Michel Deza". Optim. Letters. doi:10.1007/s11590-017-1189-7.
^ "Looking for the Right
Hand - DiscoverMagazine.com".
discovermagazine.com. Retrieved 23 March 2018.
^ a b "Quantum Diaries". www.quantumdiaries.org. Retrieved 23 March
^ Organic Chemistry (4th Edition) Paula Y. Bruice.
^ Organic Chemistry (3rd Edition) Marye Anne Fox, James K. Whitesell.
^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book")
(1997). Online corrected version: (2006–) "chirality".
^ Chang, Raymond. Chemistry (second ed.). Random House. p. 660.
^ Moloney, Mícheál P.; Gun'ko, Yurii K.; Kelly, John M.
(2007-09-26). "Chiral highly luminescent CdS quantum dots". Chemical
Communications. 0 (38). doi:10.1039/b704636g.
^ Schaaff, T. Gregory; Knight, Grady; Shafigullin, Marat N.; Borkman,
Raymond F.; Whetten, Robert L. (1998-12-01). "Isolation and Selected
Properties of a 10.4 kDa Gold:Glutathione Cluster Compound". The
Journal of Physical Chemistry B. 102 (52): 10643–10646.
doi:10.1021/jp9830528. ISSN 1520-6106.
^ Ma, Wei; Xu, Liguang; de Moura, André F.; Wu, Xiaoling; Kuang, Hua;
Xu, Chuanlai; Kotov, Nicholas A. (2017-06-28). "Chiral Inorganic
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^ Solomon and Fryhles organic chemistry, Ed 10, Wiley (Students
edition), Chapter 5 (Stereochemistry), Section 5.5 More about
biological significance of chirality
^ Solomon and Fryhles organic chemistry, Ed 10, Wiley (Students
edition), Chapter 5 (Stereochemistry), review problem 5.14
^ Solomon and Fryhles organic chemistry, Ed 10, Wiley (Students
edition), Chapter 5 (Stereochemistry), section 5.11(chiral drugs)
^ Schilthuizen, M.; Davison, A. (2005). "The convoluted evolution of
snail chirality". Naturwissenschaften. 92 (11): 504–515.
Amphidromus perversus (Linnaeus, 1758)". www.jaxshells.org.
Retrieved 23 March 2018.
Handedness of the Universe by Roger A Hegstrom and Dilip K
Look up chirality in Wiktionary, the free dictionary.
Arene substitution pattern
o-, m-, p- (ortho, meta, para)
Syn and anti addition
Three identical ligands
fac, mer (facies, meridonal) [obsolete]
In carbon skelets
n, iso, neo, cyclo
Secondary and tertiary
CIP (Cahn–Ingold–Prelog) priority rules
Pseudoasymmetric (pseudochiral) centers
(+)-, (−)- or d-, l-