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Topic: Chirality

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Chirality (chemistry)

LRD

Mirror image

Chirality (mathematics)

Sharpless bishydroxylation

Handedness

Cahn Ingold Prelog priority rules

Utter West

Stereochemistry

Sharpless epoxidation

Stereoisomerism

List of organic chemistry topics

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	Chirality
		A chiral molecule is one that is not superimposable on its mirror image; it has the property of rotating the plane of polarisation of plane-polarised monochromatic light that is passed through it.
		Cyclooctatetraene is a tub-shaped molecule; its 1,2,3,4-tetramethyl derivative is chiral.
		Perchlorotriphenylamine (the 'perchloro' bit derives from the replacement of all of the hydrogen atoms with chlorine) is heavily sterically hindered and the molecule is in the shape of a propellor.
	www.rod.beavon.clara.net /chiralit.htm (993 words)

	Encyclopedia: Chirality (chemistry)
		Chiral molecules are sometimes referred to as being "dissymmetric"; chirality and dissymmetry being one in the same.
		Chirality is of critical importance in chemistry and unites the traditionally-defined subdisciplines of inorganic chemistry, organic chemistry and physical chemistry.
		The fundamental laws of physics may be chiral, as the weak charge is not invariant under a reflection unless particles are replaced by their antiparticles as well, and kaon decay appears to violate even that symmetry.
	www.nationmaster.com /encyclopedia/Chirality-(chemistry) (1794 words)

	Chirality (chemistry) - Wikipedia, the free encyclopedia
		Chirality is of interest because of its application to stereochemistry in inorganic chemistry, organic chemistry, physical chemistry and biochemistry.
		Technically, a molecule is achiral (not chiral) if and only if it has an axis of improper rotation; that is, an n-fold rotation (rotation by 360°/n) followed by a reflection in the plane perpendicular to this axis which maps the molecule onto itself.
		Chiral compounds exhibit optical activity because of the way their molecular electric fields interact with the electromagnetic waves of light.
	en.wikipedia.org /wiki/Chirality_(chemistry) (957 words)

	Petitjean's Quantitative Chirality
		Measuring chirality is one case of measuring the similarity of two classes of equivalence of distributions: the set of all translated and rotated images of the original distribution, and the set of all its translated and rotated and inverted images.
		Quantitative chirality measure is related to the theory of probability metrics [1] and the Monge-Kantorovitch transportation problem [2] for which the cost of transporting one mass distribution to another one must be minimized.
		An important consequence is that the chiral index of a parent distribution can be approximated by sampling, because the chiral index of the sample is converging to that of the parent distribution.
	www.mazepath.com /uncleal/petit.htm (2457 words)

	Chirality (Site not responding. Last check: 2007-11-02)
		In geometry, a figure is chiral (and said to have chirality) if it is not identical to its mirror image, or more particularly can't be mapped to its mirror images by rotations and translations alone.
		The word chirality is derived from the greek χειρ (cheir), the hand, the most familiar chiral object; the word Enantiomorph stems from the greek εναντιος (enantios) 'opposite' and μορφη (morphe) 'form'.
		An atom is a chiral center when the molecule it is in, regardless of the molecule's conformation, can't be made to be identical to (or super-imposable on) its mirror image by rotations and translations alone if the chiral atom's center must be super-imposable on its own mirror image position.
	www.aaaah.org /wiki/en/ch/Chirality.htm (696 words)

	Michel PETITJEAN homepage / The Mathematical Theory of Chirality
		Chirality is sensitive to the dimension of the space: a non isocele triangle is chiral in the plane, and is achiral in the 3D space.
		The chiral index should not depend of which particular mirror is selected to generate the mirror image, and the chiral index should be insensitive to any isometric transformation of the distribution.
		It is why the quantitative measure of chirality is a problem related to the theory of probability metrics [1], and also to the Monge-Kantorovitch transportation problem [2], for which the cost of transporting a distribution of mass to an other one has to be minimized.
	petitjeanmichel.free.fr /itoweb.petitjean.html (2862 words)

	Chirality - Wikipedia, the free encyclopedia
		Chirality (Greek handedness, derived from the word stem χειρ~, ch[e]ir~ - hand~) is an asymmetry property important in several branches of science.
		An object or a system is called chiral if it differs from its mirror image.
		The chirality or optical isomerism in some molecules in the study of chemistry.
	en.wikipedia.org /wiki/Chirality (173 words)

	No. 604: Chemical Chirality
		Chemists call this property "chirality." It comes from the Greek word for hand.
		Thalidomide, which created so many birth defects in the 1950s, is chiral.
		The drug was put on the market with both forms present, and it did untold damage.
	www.uh.edu /engines/epi604.htm (447 words)

	Chirality (Site not responding. Last check: 2007-11-02)
		This is an important characteristic of the carbon atom, which arises from the ability of the C atom to form tetrahedral structures.
		If the chirality property has no effect on the function of the molecule then it should be safe to use racemic mixture.
		A particularly tragic example in attributed to chirality occurred in early 1960's when a synthetic tranquilliser thalidomide was widely prescribed as a sedative.
	www-biol.paisley.ac.uk /courses/stfunmac/glossary/chirality.html (491 words)

	Describing Chirality: Home page
		Basically, chirality is "handedness," that is the existence of left/right opposition.
		This background is to be kept in mind when appreciating the importance of chirality, whether in science or in everyday life.
		Chirality is an old theme in many branches of chemistry and biology, with overwhelming practical importance, and physicists have long paid interest in symmetry matters.
	chirality.ouvaton.org /homepage.htm (682 words)

	Online Guide to Chiral HPLC (Site not responding. Last check: 2007-11-02)
		For chiral resolution to occur, a portion of the molecule must enter the hydrophobic cavity and a hydrogen bonding region of the molecule must interact with the mouth of the cavity.
		Chiral synthesis requires a chiral starting point, it is complex and requires care to avoid racemisation.
		Chiral stationary phases offer several advantages, the solutes are unmodified, the separations are rapid (useful for labile or racemizing compounds) and the separation relies on a multi-step process.
	www.raell.demon.co.uk /chem/CHIbook/Chiral.htm (6412 words)

	Stereoisomers
		In order to determine the true or "absolute" configuration of an enantiomer, as in the cases of lactic acid and carvone reported here, it is necessary either to relate the compound to a known reference structure, or to conduct a rather complex X-ray analysis on a single crystal of the sample.
		In the case of 2,3-dihydroxybutanedioic acid, known as tartaric acid, the two chiral centers have the same four substituents and are equivalent.
		Note that a conformation having a 90º dihedral angle is achiral, as a consequence of a plane of symmetry.
	www.cem.msu.edu /~reusch/VirtualText/sterism3.htm (4155 words)

	id_mole_chiral.html (Site not responding. Last check: 2007-11-02)
		Because enzymes and their substrates may be chiral, it is useful to understand how achiral and chiral molecules can interact.
		Chiral molecules are nonsuperposable with their mirror images.
		To determine if a molecule is chiral using the superposability requirement, build a molecular model of the molecule in question, then a build a mirror image of this model.
	web.chem.ucla.edu /~harding/tutorials/stereochem/id_mole_chiral.html (994 words)

	Chirality (mathematics) - Wikipedia, the free encyclopedia
		Many other familiar objects exhibit the same chiral symmetry of the human body (or enantiomorphic) —gloves, glasses, shoes, legs on a pair of pants, etc. A similar notion of chirality is considered in knot theory, as explained below.
		Its symmetry group is a frieze group generated by a single glide reflection.
		For example the unknot and the figure-eight knot are achiral, whereas the trefoil knot is chiral.
	en.wikipedia.org /wiki/Chirality_(mathematics) (553 words)

	Stereochemistry (Site not responding. Last check: 2007-11-02)
		A molecule is chiral if there is no internal plane of symmetry, and the molecule and its mirror image are not superimposable.
		To distinguish between the two possible arrangements of 4 substituents around a chiral carbon molecule, a system of nomenclature was developed.
		A chiral molecule and its mirror image molecule are called stereoisomers or enantiomers.
	web.mit.edu /esgbio/www/chem/stereo.html (594 words)

	Describing Chirality: Research results
		Chirality is only defined negatively; the chiral objects are the objects that fail to be achiral.
		It was mathematically proved that chirality is amenable to a rich description for a large class of objects that includes molecules.
		This approach was called the gauge description of chirality, because it is associated with a new class of geometries called gauge geometries.
	www.chiral.com /description/research.htm (621 words)

	Studying Chirality with VCD
		Chirality is a chemical property that is very important to current pharmaceutical development processes.
		In the past, manufacturing processes for drugs ignored chirality, and whatever mixture of enantiomers was produced synthetically was used.
		For example, NMR shift reagent measurements require finding suitable chiral reagents (which shift some of the resonances for the two enantiomers in opposite directions), which can be difficult, and the technique is also problematic when the molecule contains multiple chiral centers.
	www.gaussian.com /g_whitepap/vcd.htm (1293 words)

	Kalée Gregory: Chirality Module Design (Site not responding. Last check: 2007-11-02)
		Chirality is an intersting and important topic in chemistry, and chirality in molecules is detected with light.
		However, chirality is a subject that is not treated in high school curricula.
		In lab, various activities on polarization, symmetry, and chirality would give the students a means for choosing a project on one of those topics to explore during the second half of the quarter.
	kalee.tock.com /portfolio/chirality.html (523 words)

	B and C
		For example, according to the latter view, a meso-compound is considered to be composed of two chiral parts of opposite chirality sense; this usage is to be discouraged.
		For example with an allene abC=C=Ccd the chiral axis is defined by the C=C=C bonds; and with an ortho-substituted biphenyl the atoms C-1, C-1', C-4 and C-4' lie on the chiral axis.
		A chirality centre is thus a generalised extension of the concept of the asymmetric carbon atom to central atoms of any element, for example N
	www.chem.qmul.ac.uk /iupac/stereo/BC.html (1536 words)

	Fundamental aspects of chirality
		True chirality is shown by systems existing in two distinct enantiomeric states that are interconverted by space inversion, but not by time reversal combined with any proper spatial rotation.
		A good example of a truly chiral influence is a static magnetic field collinear with an unpolarized light beam which is therefore able to induce absolute enantioselection in all circumstances, including a reacting system allowed to reach thermodynamic equilibrium.
		Reactions of chiral molecules in the presence of a time-noninvariant enantiomorphous influence: a new kinetic principle based on the breakdown of microscopic reversibility.
	www.chem.gla.ac.uk /~laurence/Chirality.htm (397 words)

	Joao Aires-de-Sousa / Research / Cheminformatics: chirality, NMR
		This code is a molecular transform that represents chirality using a spectrum-like, fixed-length code, and includes information about the geometry of chiral centers, properties of the atoms in their neighborhoods, bond lengths, and distinguishes between enantiomers.
		However, it is restricted to applications in which the chirality arises from a chiral carbon (or at least a chiral atom).
		More recently we proposed a second chirality code that characterizes the chirality of a 3D structure considered as a rigid set of points (atoms) with properties (atomic properties) and connected by bonds.
	www.dq.fct.unl.pt /qoa/jas/research.htm (970 words)

	Measuring the degree of chirality (Site not responding. Last check: 2007-11-02)
		Likewise we may feel that We may feel that iodobutane is more chiral than fluorobutane, because the iodine atom is much larger that the fluorine atom; and that corronenylbutane may not be so chiral because corronene is a large a achiral molecule, and the butane chain is only a small disturbance to it.
		Chirality is measurable when coordinates of atoms are given, or when contours are used (II-1).
		The measurement of chirality, or bilaterality, can be applied to many other domains, such as archeology, evolutionary biology and more.
	alpha.ch.huji.ac.il /chirality (445 words)

	Chapter 7: Chirality Centre
		In its simplest and most common case, a chirality center is characterised by an atom that has four different groups bonded to it in such a manner that it has a non-superimposable mirror image.
		The presence of a single chirality centre in a molecule results in a chiral molecule fundamentally because the top, bottom, left, right, front and back faces are all different.
		Chiral molecules that possess two or more chirality centers, have stereoisomers that may be either enantiomers or diastereomers.
	www.chem.ucalgary.ca /courses/351/Carey5th/Ch07/ch7-3.html (472 words)

	Enatiomers and Chirality (Site not responding. Last check: 2007-11-02)
		Enantiomers are stereoisomers that exhibit a property known as chirality.
		These chiral molecules have certain characteristics which are different from other molecules that do not exhibit chirality.
		Such a molecule would be chiral possessing no internal plane of symmetry and having a non-superimposible mirror image.
	members.aol.com /logan20/chiral.html (680 words)

	Origin of life: the chirality problem
		A tragic reminder of the importance of chirality is thalidomide.
		Even if modern clays did have a chiral bias, this could be due to previous absorption of optically active biomolecules (which are, of course produced by living things).
		One attempt to solve the chirality problem was proposed by Russell Doolittle, a professor of biochemistry at the University of California at San Diego, and an atheist.
	www.answersingenesis.org /docs/3991.asp (2841 words)

	chirality
		The concept of "chirality" has been known in chemistry since the 1870's although it would be nearly a hundred years before chemists began using this term.
		The term Chiral is derived from the greek name kheir meaning "hand" and apparently was coined by Lord Kelvin in 1904, in his Baltimore Lectures on Molecular Dynamics and the Wave Theory of Light in which he stated...
		These rules are incorporated in the chirality monitor of Accelrys DS Viewer and Discovery Studio Visualizer (which is free).
	www.leffingwell.com /chirality/chirality.htm (1293 words)

	Chirality (Site not responding. Last check: 2007-11-02)
		It was produced as a mixture of both the L and D molecules (mixed chirality).
		The drug companies learned a good lesson from this and are now heavily investing in chiral research to determine which molecular spin direction makes the most efficient and safe drug.
		The concept of chirality is very important in skin care because the body’s receptors are all chiral.
	65.110.92.137 /NuCell/Chirality.htm (506 words)

	Chirality and the Origin of Life (Site not responding. Last check: 2007-11-02)
		The origin of the homochirality of biological molecules (the use in living organisms of only left-handed or L-amino acids and right-handed or D-sugars) has puzzled scientists since the chirality of molecules was discovered by Louis Pasteur more than 150 years ago.
		Recently it has been discovered that an excess of L-amino acids is present in the Murchison and Murray meteorites indicating that a preference for L-amino acids existed in solar system material before there was life on Earth.
		In this model the action of circular polarized light on interstellar chiral molecules introduced a left handed excess into molecules in the material from which the solar system formed.
	www.ast.cam.ac.uk /AAO/local/www/jab/astrobiology/chirality.html (394 words)

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