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Topic: Stereogenic

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	R/S - Two Stereogenic Centers
		Diastereoisomers may be recognized because they are connected identically, they have two (or more) stereogenic atoms and comparison of those atoms reveals that the relationship at one (or more) atom is identical and the relationship at the other (or more) atom is mirror-image.
		Since the diastereoisomer we made by changing the top stereogenic carbon of our original compound is not superimposable upon its mirror image, it too is optically active and has a mirror image enantiomer.
		The four atoms or groups attached to the top stereogenic carbon are the same as those attached to the bottom stereogenic carbon.
	chemistry2.csudh.edu /rpendarvis/RS-2Sterctr.html (1533 words)

	JCE 2005 (82) 1031 [Jul] Stereogenic Centers and Axes: A Comparison of the Chiral Topologies Available to Cabcd and ...
		Chirality in molecules incorporating a stereogenic center can be fully explained using the regular tetrahedron as a model.
		Analysis of chirality in molecules incorporating a stereogenic axis, on the other hand, requires the use of a less regular, “stretched” or “extended”, tetrahedron.
		Molecules incorporating a stereogenic center have a single chiral topology in which all four substituents are necessarily different.
	jchemed.chem.wisc.edu:8000 /Journal/issues/2005/Jul/abs1031.html (344 words)

	Basic Concepts of Stereochemistry
		Such an asymmetrically substituted carbon atom is a stereogenic centre and is the commonest source of chirality in organic molecules.
		Molecules possessing more than one stereogenic centre also exhibit diastereoisomerism because inverting one or more (but not all) of the centres leads to structures which do not have a mirror image relationship with the original.
		describes a molecule that is achiral, despite possessing stereogenic centres, due to the presence of an internal mirror plane.
	users.ox.ac.uk /~mwalter/web_05/year1/stereochemistry/basics.shtml (1308 words)

	ISOMERISM AND STEREOCHEMISTRY
		If the atoms at this point are still the same, then move further from the stereogenic centre (and so on) until the point of difference is found (there must be a point of difference somewhere for the molecule to be chiral).
		The two stereogenic centres have identical substituents and one of the possible stereoisomers of this compound has an internal mirror plane such that C2 is one mirror image of C3.
		This is because the rotation of plane polarised light by one stereogenic centre within the molecule is equal and opposite to the rotation caused by the other (mirror image) stereogenic centre, and the two effects cancel.
	www.chem.usyd.edu.au /~george/isomers.html (965 words)

	Stereoisomers
		In the CIP system of nomenclature, each stereogenic center in a molecule is assigned a prefix (R or S), according to whether its configuration is right- or left-handed.
		The stereogenic carbon atom is colored magenta in each case, and the sequence priorities are shown as light blue numbers.
		In cases having two adjacent stereogenic centers, such as this, the prefixes erythro and threo may be used to designate the relative configuration of the centers.
	www.cem.msu.edu /~reusch/VirtualText/sterism3.htm (4155 words)

	stereochemistry (Site not responding. Last check: 2007-11-05)
		The stereogenic center(s) in one enantiomer has(have) the opposite configuration(s), meaning R or S designation, as in the other enantiomer.
		All molecules are chiral when they have one stereogenic carbon, but not all molecules with 2 stereogenic carbons are chiral.
		Every stereogenic center can be classified by the Cahn-Ingold-Prelog sequence rules to assign priority which are based on atomic number, as being R or S. specific rotation: a physical constant of a pure, chiral compound.
	www.uncwil.edu /chem/chmlab211martin/stereochemistry.htm (415 words)

	Stereogenic - Wikipedia, the free encyclopedia
		In chemistry a stereogenic center is often mistaken for a chiral center.
		Second, a stereogenic center of a molecule produces stereoisomerism.
		The molecule, however, does not have to be a chiral molecule, i.e.
	en.wikipedia.org /wiki/Stereogenic (104 words)

	[No title]
		The most prevalent stereogenic centers in organic chemistry are carbon atoms, which have four different groups bound to them.
		The more common of these atoms, with which an organic chemist should be familiar, are Si, N and P. They may be tetrahedral molecules (where the four different groups are atoms) or trigonal pyramidal molecules (where a lone pair is included as one of the four different groups).
		In this case, even though a stereogenic center is present, the molecules are optically inactive as the optical activity of the two extremes of inversion averages out.
	www.mhhe.com /physsci/chemistry/carey/student/olc/graphics/carey04oc/ref/ch07stereogenic.html (369 words)

	chirality (Site not responding. Last check: 2007-11-05)
		The carbon atom with four different groups connected to it is the stereogenic center of that chiral compound.
		The primary criterion for molecular chirality is of course the presence of a stereogenic center.
		This molecule is chiral because the central carbon atom is stereogenic.
	www.wiu.edu /users/mftkv/Chemistry102/chirality.html (352 words)

	Assymetric Induction
		When the existing stereogenic center is located next to the carbonyl group, as in the upper equation, it may influence the proportion of product diastereomers to a significant degree.
		Because the new stereogenic centers are vicinal, this is termed 1,2-diastereoselectivity, and is the same for both an enantiomerically pure or a racemic reactant.
		If, however, the stereogenic center is far away from the carbonyl group, it has a negligible influence on the reduction, and a nearly 50:50 mixture of diastereomers is produced (lower example).
	www.cem.msu.edu /~reusch/VirtualText/sterslct.htm (8654 words)

	Drawing Sugar Structures - Fischer, Haworth, Chair (Site not responding. Last check: 2007-11-05)
		To illustrate the ambiguity in the configuration at this new stereogenic center, squiggly lines are used in the drawing to connect the hydrogen and the hydroxyl group to
		As was done previously, the ambiguity of configuration at this new stereogenic center is indicated by using squiggly lines to represent the bonds to the H and OH on the hemiacetal carbon atom.
		The bonds to the groups attached to the ring carbons are drawn by using vertical lines to indicate whether a group is oriented to the top face or to the bottom face of the ring.
	www.rocky.edu /~barbaroj/sugars/sugars.html (1410 words)

	Fu-17
		The answer is yes, and thus the stereogenic units occur only in the groups attached to the fullerene core.
		Superimposition of stereogenic elements in a fullerene molecule.
		Explanation: The chiralities of the stereogenic centers in the esters are superimposed on the descriptor for the fullerene with the inherently chiral substitution pattern.
	www.chem.qmul.ac.uk /iupac/fullerene/Fu17.html (2346 words)

	Assigning Absolute Configurations for Fischer Projections (Site not responding. Last check: 2007-11-05)
		In the lecture notes, you saw that Fischer Projections were a type of short hand for representing molecules with stereogenic centers developed by biochemists.
		At stereogenic centers, horizontal bonds were pointing towards you (wedges) and vertical lines were pointing away from you (dashes).
		First, of the 4 substituents on the stereogenic, one is held in position.
	www.ipfw.edu /chem/261/Fischer1.htm (237 words)

	Ans4 (Site not responding. Last check: 2007-11-05)
		The third molecule has four different groups bonded to the central carbon, a stereogenic carbon, hence the molecule is stereogenic.
		Stereogenic center is a center, typically a carbon, in a molecule that has four different groups bonded to it.
		A meso compound is a molecule, which typically has two stereogenic centers, in which its mirror image is the same as the molecule.
	www2.tltc.ttu.edu /headley/Ans4.htm (245 words)

	11th Hour - Organic Chemistry I & II
		It may be simpler or less confusing to describe objects as either "chiral" or "not chiral" but many chemists use the term "achiral" to mean the opposite of chiral.
		Assigning R or S absolute configuration around each stereogenic center is slightly more complicated but requires no skills that we have not already learned.
		Recall that if the lowest priority ligand is pointed toward the viewer, the apparent motion of the eye going from highest to lowest priority would actually be the opposite of what it would be if the lowest priority ligand were oriented away from the viewer.
	www.blackwellpublishing.com /11thhour/book6/oc1ch5.html (441 words)

	Enantiomerism and Configuration
		Configuration is the arrangement of the groups attached to a stereogenic center.
		In one enantiomer the arrangement is clockwise around the stereogenic carbon beginning with the highest priority atom or group.
		For example if one group attached to the stereogenic center is a methyl group, the three Hydrogens would each have an atomic number of one for a total of three (1+1+1).
	members.aol.com /logan20/configur.html (1266 words)

	Chapter 7: The Stereogenic Centre
		The presence of a single stereogenic centre in a molecule results in a chiral molecule.
		The most prevalent stereogenic centres in organic chemistry are carbon atoms, which have four different groups bound to them.
		In this case, even though a stereogenic centre is present, the molecules are optically inactive as the optical activity of the two extremes of inversion averages out.
	library.tedankara.k12.tr /carey/ch7-3.html (369 words)

	Chapter21
		It is often difficult to draw the 3D structures of molecules that contain stereogenic centers.
		The aldehyde group and the CH OH groups are in the plane of the paper (screen) that has the stereogenic carbon.
		Now imagine that you hold the C-H bond and tilt the molecule so that the H and OH groups are now pointing towards you and the other two groups are pointing away from you as in the middle structure.
	www.wiu.edu /users/mftkv/Chemistry102/Chapter16.htm (1498 words)

	Chem 341 - Announcements
		For n-number of stereogenic centers, there are 2n possible stereoisomers.
		- Molecules which have stereogenic centers, but are achiral (they are identical with their mirror image).
		If a molecule already has a stereogenic center, diastereomers are produced, and they may not be formed in equal amounts.
	www.ndsu.nodak.edu /instruct/grcook/chem341_97/lecture7.html (388 words)

	Beilstein Journal of Organic Chemistry \| Full text \| Conformational rigidity of silicon-stereogenic silanes in ...
		[1-4] Aside from the use of silicon-stereogenic chiral auxiliaries in substrate-controlled reactions, [5] a still limited number of remarkable stereoselective processes with a stereogenic silicon as the reactive site were reported, [6] namely the inter- [7] as well as intramolecular [8] chirality transfers from silicon to carbon.
		The newly formed stereogenic carbon is directly connected to the former source of chiral information.
		The stereogenic carbon in the alcohol is not directly involved in the actual bond formation.
	bjoc.beilstein-journals.org /content/3/1/9 (1376 words)

	Patents in Class 435/137
		Furanosides or pyranosides can be reacted with pyruvate and converted into sialic acids in good yields by an enzymatic synthesis, using a suitable aldolase, where the concentration of aldolase, per 50 mM of pyruvate, is 1 to 2,500 U*/ml....
		The present invention provides a ketoaldonic acid such as an octulosonic or nonulosonic acid having a formed stereogenic center of R configuration, as well as methods of synthesizing the same.
		The invention relates to a process for the preparation of fatty acid partial esters of polyols, the fatty acid partial esters thus obtainable, and their use.
	www.freepatentsonline.com /CCL-435-137.html (1942 words)

	JCE 2000 (77) 866 [Jul] The R/S System: A New and Simple Approach to Determining Ligand Priority and a Unified Method ...
		A new approach providing an "at-a-glance" priority order of ligands attached to a stereogenic center in organic molecules and a unified method for assigning and correlating stereogenic center absolute configuration in diverse stereochemical representations is presented.
		For a stereogenic center, any two ligands in a plane are chosen and then linked by a clockwise arc taking the stereogenic atom as the geometric center.
		The stereoformula is then transformed into a Fischer projection in which the ligands at the initial and final positions of the clockwise arc occupy the vertical top and vertical bottom, and those in front and in the rear take up the horizontal right and horizontal left positions, respectively.
	jchemed.chem.wisc.edu:8000 /Journal/Issues/2000/jul/abs866.html (345 words)

	Seven Carbon Alkene with one Stereogenic Center
		I can't figure out the structure of a seven carbon alkene that has a stereogenic center (chiral center) and is known to be optically active.
		A stereogenic atom is an atom where the exchange of any two groups gives a different molecule.
		The stereogenic center could also be a chiral carbon such as 3-methyl-1-hexene, which also only has one stereogenic center.
	www.physicsforums.com /showthread.php?t=44206&goto=nextoldest (244 words)

	Elsevier MDL :: Company Information :: News :: Press Releases :: 2003 (Site not responding. Last check: 2007-11-05)
		The new, enhanced stereochemical representation meets the industry need for a detailed description of stereogenic centers within a chemical structure, including a relative stereochemical representation.
		By storing this information at the stereogenic center, rather than at the level of the whole structure, the new representation enables the chemist to differentiate between absolute and relative stereogenic centers in a single structure.
		As well as allowing relative configurations, the new representation permits different configurations to be stored for each center or group of centers, enabling the chemist to specify more than one relative grouping of stereogenic centers.
	www.mdli.com /company/news/press_releases/2003/pr_stereochemrep_07apr03.jsp (592 words)

	[No title] (Site not responding. Last check: 2007-11-05)
		The process of the present invention comprises the step of heating a malonate ester of structural formula II in a suitable reaction solvent in the presence of a silylating reagent in the absence of added base.
		The term "enantiomeric excess"is synonymous with the term"optical purity." The term"enantioselective"shall mean a reaction in which one enantiomer is produced (or destroyed) more rapidly than the other, resulting in the predominance of the favored enantiomer in the mixture of products.
		It is to be noted that the stereogenic center denoted with an * has the
	www.wipo.int /cgi-pct/guest/getbykey5?KEY=03/72042.030904&ELEMENT_SET=DECL (3770 words)

	Combinatorial Stereochemistry (Site not responding. Last check: 2007-11-05)
		Working out the possible stereoisomers for a number of different stereogenic centers is a problem in combinatorial algebra.
		As usual, we've tried to be systematic: R for Center 1, coupled with R or S for Center 3, and then each of those with R or S for Center 2, and so on.
		One can now proceed to draw skeletons for three stereogenic centers and fill in the ligands in the proper places to generate all eight stereoisomers.
	chemistry.umeche.maine.edu /CHY251/Combin.html (209 words)

	CH610A - Dr. Iverson/Fall 97: Stereochemistry Handout
		A carbon atom is not a stereogenic center if even two of the substituents are the same.
		A carbon atom is not a stereogenic center if even two of the substituents are the same (it was worth repeating).
		Historical note: in the past, stereogenic centers have also been called; asymmetric carbon atoms, asymmetric centers, chiral centers, or chiral atoms even though these latter names can be confusing in certain situations.
	www.chem.tamu.edu /organic/Fall98/stereo.html (842 words)

	Organic Chemistry 341 Notes
		If a molecule possesses more than one stereogenic center, the possibility for another type of stereoisomer exists.
		Configurational diastereomers occurs when there are 2 or more stereogenic centers and one or more is the same, while one or more are different.
		Molecules which have stereogenic centers, but are achiral (they are identical with their mirror image).
	www.ndsu.nodak.edu /instruct/grcook/chem341_98/lectures/lecture25.shtml (146 words)

	Lignan Plant Natural Products
		and the related agents angeloylgomisin R, gomisin O, and gomisin E. The three stereogenic centers present on the eight-membered ring and the stereogenic biaryl axis are introduced with complete control of absolute and relative stereochemistry.
		The C15/C16 stereogenic biaryl axis of interiotherin A (1) is introduced with complete control of atropdiastereoselection using an oxidative biaryl cuprate coupling.
		The sense of stereoinduction in this reaction was dependent solely upon the configuration of the C6-stereogenic center of 2, such that C6/C7-anti stereochemistry allows for complete stereocontrol of the newly formed axis.
	www.chemistry.ohio-state.edu /~coleman/lignan.htm (299 words)

	CHEM 331, Organic Chemistry I (Site not responding. Last check: 2007-11-05)
		They may or may not contain stereogenic atoms.
		Keep in mind that that if a molecule contains one stereogenic carbon it is authomaticaly chiral and exists as a pair of enantiomers (see part d below).
		However, molecule with more than one stereogenic carbons may have meso stereoisomers that are not chiral.
	www.towson.edu /~ryzhkov/handouts/stereo.html (826 words)

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