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Topic: Stereocenter

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Anomeric carbon

	[No title]
		Each atom attached to the stereocenter is assigned a priority based on its atomic number.
		If two identical atoms are attached to the stereocenter, the next set of atoms in both chains is investigated, moving away from the stereocenter until a point of difference is found.
		Consider the methyl and ethyl groups on the stereocenter.
	www.odu.edu /sci/jadamski/n9c.htm (291 words)

	stereocenter \| English \| Dictionary & Translation by Babylon
		In general, a stereocenter, or stereogenic centre, is any atom bearing groups such that an interchanging of any two groups leads to a stereoisomer.
		However, other atoms may also be stereocenters in inorganic chemistry or in carbon analogs.
		Having four different groups attached to one carbon necessarily means that it is a stereogenic center that has a hybridisation1 of sp3 and is a tetrahedral stereogenic carbon.
	www.babylon.com /definition/stereocenter (115 words)

	Reference.com/Encyclopedia/Stereocenter
		A stereocenter, or stereogenic centre, is any atom in a molecule bearing groups such that an interchanging of any two groups leads to a stereoisomer.
		The term stereocenter was introduced in 1984 by Mislow and Siegel.
		The broad term stereocenter is often confused with that of the narrower set of chirality center.
	www.reference.com /browse/wiki/Stereocenter (249 words)

	Stereocenter
		A stereocenter in organic chemistry generally refers to a carbon atom in a chemical compound that has four different types of atoms or groups of atoms attached to it.
		This type of stereocenter is otherwise known as an asymmetric carbon atom or a chiral carbon.
		A stereocenter is an atom at which the interchange of two groups produces a stereoisomer.
	www.dejavu.org /cgi-bin/get.cgi?ver=93&url=http%3A%2F%2Farticles.gourt.com%2F%3Farticle%3Dstereocenter%26type%3Den (0 words)

	Spartanburg SC \| GoUpstate.com \| Spartanburg Herald-Journal
		Any atom attached to a stereocenter or double bonded system such as that of alkenes, is given a Cahn-Ingold-Prelog priority based on the atomic number or, in the case of isotopes, the mass number.
		The general rules of CIP priorities are determined through examination of the isomer's bonded units or subunits, and their relative position to the stereocenter of the isomer.
		After the substituents of a stereocenter have been assigned their priorities, the molecule is so oriented in space that the group with the lowest priority is pointed away from the observer.
	www.goupstate.com /apps/pbcs.dll/section?category=NEWS&template=wiki&text=Cahn_Ingold_Prelog_priority_rules (0 words)

	[No title]
		To name a stereocenter, we assign priority to the groups attached to the stereocenter, then apply a label based upon the direction in which priorities decrease.
		Change your view of the molecule so that you are looking along the bond between the stereocenter and the lowest priority group, with the lowest priority group facing away from you.
		The four atoms attached to the stereocenter are iodine and three carbons.
	www.brookscole.com /chemistry_d/templates/student_resources/0534166962_brown/tutorials/stereochem/r_s.html (0 words)

	Stereochemistry tutorial: Enantiomers and Diastereomers
		Stereocenters, (sometimes called chiral centers, or stereogenic centers) are carbons that have four non-identical substituents on them, and are designated as either of R stereochemistry or S stereochemistry.
		If a molecule has one stereocenter of R configuration, then in the mirror image of that molecule, the stereocenter would be of S configuration, and vice-versa.
		If the curve goes in a counterclockwise direction, then that stereocenter is of S configuration.
	www.chemhelper.com /enantiomers.html (0 words)

	id_stereocenter.html (Site not responding. Last check: 2007-10-31)
		Discussion: A stereocenter is a carbon atom that has four different attachments.
		It is not necessary for a molecule to have a stereocenter to be chiral.
		Because stereocenters are the origin of chirality of most chiral organic molecules, it is useful to be able to recognize stereocenters within a molecule.
	web.chem.ucla.edu /~harding/tutorials/stereochem/id_stereocenter.html (0 words)

	Media Portfolio
		To assign an R or S configuration to a stereocenter of a chiral molecule, the Cahn-Ingold-Prelog system is used to assign relative priorities to all of the groups attached to the stereocenter.
		The second step in determining the configuration of a chiral stereocenter is to orient the lowest-priority group behind the stereocenter and determine whether the remaining groups are priority-ordered in a clockwise or counterclockwise fashion around the stereocenter.
		If groups are ordered around a chiral stereocenter such that the lowest-priority group is behind the stereocenter and the remaining groups are in front of the stereocenter and ordered clockwise around the stereocenter in ascending priority-numbered order (i.e., 1 to 3 for carbon), the chiral stereocenter is assigned an "R" designation.
	wps.prenhall.com /wps/media/objects/724/741576/chapter_05.html (1341 words)

	Section Two
		To understand the meaning of the term "stereocenter" and to be able to identify the stereocenters given a structural formula.
		To be able to describe the difference between enantiomers and diastereomers and to identify a pair of enantiomers or diastereomers given their structures.
		To further see how the mirror image 2-bromobutane molecules have a different orientation of their atoms in space, hold the models (one in each hand) in front of you so that the hydrogens attached to carbon 2 are towards the back (pointing away from you).
	erkki.kennesaw.edu /schem215/sc00009.htm (719 words)

	7.2.3 Example executions (Site not responding. Last check: 2007-10-31)
		If the stereocenter does not have a specified stereochemistry, flipper will generate moleucles with each of the stereochemistry states at each stereocenter.
		This execution will differ from the first in that all stereocenters will be enumerated, regardless of whether the stereochemistry is specified in the input file.
		For molecules with more than 6 stereocenters, a random set of 64 isomers will be generated from the larger set of potential stereoisomers.
	www.eyesopen.com /docs/html/omega/node35.html (0 words)

	Efficient Chemoenzymatic Synthesis of Pelitrexol via Enzymic Differentiation of a Remote Stereocenter
		The introduction of an oxalamic ester adjacent to the stereocenter dramatically enhanced an enzyme's enantioselectivity for hydrolysis at the terminal ester, producing the desired S-acid with high optical purity and yield.
		Clearly, introducing an oxalamic ester group on the piperidine nitrogen amplifies the chirality of this stereocenter, resulting in a dramatic enhancement on enzyme differentiation of this six-bond-distant remote chiral center.
		In this manner, overall yields of the desired acid were increased from 38% to greater than 52% after only one round of recycling the undesired enantiomer, significantly improving the efficiency and throughput of the entire synthesis (Scheme 5).
	pubs.acs.org /cgi-bin/sample.cgi/orlef7/2006/8/i08/html/ol0602755.html (0 words)

	Stereochemistry Tutorial
		This entails you to find the stereocenter first and then label the groups attached to it in order of their priority.
		The top stereocenter is an R configuration and the bottom stereocenter is an S configuration.
		For B the stereocenter is an S. does not have to be considered because there are two of the same groups attached, and is not chiral.
	facultystaff.vwc.edu /~jeaster/courseinfo/Tutorials/stereochemistryl.html (0 words)

	Reference.com/Encyclopedia/SN1 reaction
		Because the intermediate carbocation is planar, the central carbon is not a stereocenter.
		Even if it were a stereocenter prior to becoming a carbocation, the original configuration at that atom is lost.
		In fact, if the central carbon is the only stereocenter in the reaction, racemization may occur.
	www.reference.com /browse/wiki/SN1 (717 words)

	Problem Assist! for Solomons/Fryhle 7E Organic Chemistry (Site not responding. Last check: 2007-10-31)
		A tetrahedral stereocenter is sp3 hybridized and has four different groups bonded to it.
		The point of the inside-out umbrella is the stereocenter and the end of the handle is the lowest priority group.
		Remember, while we do this it is essential that we view down the length of the bond from the stereocenter to lowest priority group, with the lowest priority group farthest away from us.
	rainier.chem.plu.edu /SF7_Organic/ProblemAssist!/pa5-3b.htm (305 words)

	Chem 265H — Organic Chem I (Site not responding. Last check: 2007-10-31)
		Be able to determine whether a molecule is chiral or achiral by (1) deciding whether the mirror image is the same or different from the original structure, or (2) determining whether an internal plane of symmetry or an inversion center exists in any conformation.
		Recognize atoms that are stereocenters (I'm not going to make a distinction between the terms "stereocenter", "chirality center", and "asymmetric atom" - this is an introductory organic course, not an advanced course in stereochemistry) whether they are drawn to show three-dimensional geometry or not.
		Be able to assign the configuration of a stereocenter as R or S. Be able to draw a molecule with the R or S configuration requested.
	people.umass.edu /gjsnyder/Ch5H.html (478 words)

	Fischer Projections (Site not responding. Last check: 2007-10-31)
		This is tantamount to rotating about a σ-bond in the molecule (i.e., changing the conformation of the molecule), so it does not result in any change in the configuration of the tetrahedral center.
		Start out by determining the relative priorities of the four substituents attached to the stereocenter by using atomic number priorities as usual.
		Remember that to correctly assign a configuration at a stereocenter you need to orient the structure so that the lowest priority group is pointing away from you.
	cobalt.rocky.edu /~barbaroj/fischer/fischer.html (990 words)

	SparkNotes: Enantiomers and Diastereomers: Diastereomers
		For these compounds, we can produce the enantiomer by changing the configuration at that stereocenter; that is, the enantiomers differ only in their spatial arrangements at the stereocenter.
		Figure 2.1: The enantiomer of a chiral molecule with a single stereocenter is produced by inverting the configuration at that stereocenter.
		A compound that contains multiple stereocenters but is achiral due to an internal mirror plane is called a meso compound.
	www.sparknotes.com /chemistry/organic3/enantiomersanddiastereomers/section2.rhtml (474 words)

	Changing Molecular Topology
		All R stereocenters change to S, and vice versa, creating the enantiomer of the original molecule.
		If you do not know the absolute configuration of two or more atoms in a molecule, but you know their relative stereochemistry, you can specify that they are members of a relative stereochemical set.
		If the molecule has one set of relative stereocenters, the conformer generation process produces conformers that fulfill the requirements for the relative set.
	www.scripps.edu /rc/softwaredocs/msi/catalyst45/help/VCPChangeTopology.doc.html (0 words)

	7.1 Theory
		Flipper uses graph algorithms to determine which atoms are stereocenters.
		If a stereocenter has a designated stereochemistry, by default flipper does not change the stereochemistry.
		However, if a stereocenter does not have a specified stereochemistry, flipper will enumerate both stereochemistry states of the stereocenter.
	www.eyesopen.com /docs/html/omega/node31.html (0 words)

	Stereochemical Glossary
		In carbohydrates with multiple stereocenters, the stereocenter furthest from the C in the aldehyde or carboxylic acid oxidation state determines the absolute stereochemistry.
		Group A bound to a stereocenter has higher priority than group B bound to the same stereocenter when the first atom in group A has a higher atomic number than the first atom in group B. If the first atoms have the same atomic number, the second atoms are compared, etc.
		The stereocenter has the R configuration if the three remaining groups are arranged clockwise from highest to lowest priority.
	www.chem.uky.edu /research/grossman/stereo/stereogloss.html (3333 words)

	Aldol reaction Summary
		In the case of an E enolate, the dominant control element is allylic 1,3-strain whereas in the case of a Z enolate, the dominant control element is the avoidance of 1,3-diaxial interactions.
		For clarity, the stereocenter on the enolate has been epimerized; in reality, the opposite diastereoface of the aldehyde would have be attacked.
		In the syn-selective reactions, both enolization methods give the Z enolate, as expected; however, the stereochemical outcome of the reaction is controlled by the methyl stereocenter, rather than the chirality of the oxazolidinone.
	www.bookrags.com /Aldol_reaction (2537 words)

	13.8. Solution (Site not responding. Last check: 2007-10-31)
		Since all four groups are not different, it is not a stereocenter.
		The two carbon atoms in the ring are the same, so all four groups around the red carbon are not different.
		The two carbon atoms in the ring are no longer the same because one is attached to a carbon bound to a methyl group, while the other is bound to a carbon attached to a hydrogen atom.
	www.pearsoncustom.com /wertz/a_cd/cams/html/c13_organic/s03_isomr_09_xa_13_8__soln.html (143 words)

	Fischer used the results of three characteristic reactions of aldoses to demonstrate the configuration of glucose
		A new stereocenter is formed at what was the carbonyl carbon.
		This stereocenter could be of either configuration, so a pair of diastereomers is formed.
		The rest of the stereocenters would then be specified by relation to C-5.
	www.cornellcollege.edu /chemistry/courses/cardon/organic/fishpruf.html (713 words)

	Experimental Question: the Saved by the Bell edition (Site not responding. Last check: 2007-10-31)
		The question posed is whether or not the formation of a new stereocenter as the reaction goes from molecule 11 to 13 will bring forth any complications.
		From 11 to 13 when a new stereocenter is formed it will be the only stereocenter in the molecule.
		This means that with only one stereocenter there can only be enantiomers.
	www.umich.edu /~chemh215/W02HTML/SSG3/ssg2/quest.htm (171 words)

	stereocenter
		stereocenter is one of the topics in focus at Global Oneness.
		DOB has a stereocenter and R-(-)-DOB is the more active stereoisomer.
		DOM has a stereocenter and R-(-)-DOM is the more active stereoisomer.
	www.experiencefestival.com /stereocenter (0 words)

	Stereoisomers (Site not responding. Last check: 2007-10-31)
		with 2 stereocenters and 4 different atoms or groups of atoms bonded to each stereocenter.
		Each stereocenter is bonded to at least one atom or group that is different from the atoms or groups bonded to the other stereocenter (R'' and R''' in the general formula above).
		In this case, two of the mirror image models (the bottom pair) have an internal plane of symmetry and are thus achiral and represent the same molecule.
	classweb.gmu.edu /sslayden/graphics/stereo-pics.htm (169 words)

	Towards a general model for protein-substrate stereoselectivity -- Sundaresan and Abrol 11 (6): 1330 -- Protein Science
		and the topological distribution of stereocenters in the substrate.
		to stereocenter C1 in the molecule, and the amino and
		-methylnoradrenaline in a (2-2) configuration, a (catechol) and b (—OH) on the C1 stereocenter along with c (—NH) and d (—CH) on the C2 stereocenter.
	www.proteinscience.org /cgi/content/full/11/6/1330 (0 words)

	JCE 2006 (83) 1793 [Dec] Precision in Stereochemical Terminology
		Many organic chemists have begun to use the Mislow term stereocenter (or stereogenic atom) as an alternative to the traditional term asymmetric carbon atom and the slightly broader IUPAC term chirality center.
		Asymmetric carbon atoms are defined structurally, and students can easily find them to use as a tool to help in understanding the stereochemistry and finding the stereoisomers.
		This article recommends that instructors use the precise terms asymmetric carbon atom and chirality center when they apply, and use the broader term stereocenter only when there is a need to include stereogenic atoms that are not chirality centers.
	jchemed.chem.wisc.edu /Journal/Issues/2006/Dec/abs1793.html (292 words)

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