WordNet

of or belonging to neither the right nor the left politically or intellectually
a building dedicated to a particular activity; "they were raising money to build a new center for research" (同)centre
(American football) the position of the player on the line of scrimmage who puts the ball in play; "it is a centers responsibility to get the football to the quarterback"
a position on a basketball team of the player who participates in the jump that starts the game
the position on a hockey team of the player who participates in the face off at the beginning of the game
a place where some particular activity is concentrated; "they received messages from several centers" (同)centre
the sweet central portion of a piece of candy that is enclosed in chocolate or some other covering (同)centre
the object upon which interest and attention focuses; "his stories made him the center of the party" (同)centre, center of attention, centre of attention
an area that is approximately central within some larger region; "it is in the center of town"; "they ran forward into the heart of the struggle"; "they were in the eye of the storm" (同)centre, middle, heart, eye
a point equidistant from the ends of a line or the extremities of a figure (同)centre, midpoint
a cluster of nerve cells governing a specific bodily process; "in most people the speech center is in the left hemisphere" (同)centre, nerve_center, nerve centre
(football) the person who plays center on the line of scrimmage and snaps the ball to the quarterback; "the center fumbled the handoff" (同)snapper
(basketball) the person who plays center on a basketball team
(ice hockey) the person who plays center on a hockey team
politically moderate persons; centrists
the middle of a military or naval formation; "they had to reinforce the center"
move into the center; "That vase in the picture is not centered" (同)centre
equally distant from the extremes (同)halfway, middle, midway
a fractional monetary unit of several countries
(American football) putting the ball in play by passing it (between the legs) to a back; "the quarterback fumbled the snap" (同)snap
being or placed in the center

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/05/18 20:36:43」(JST)

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A stereocenter or stereogenic center is an atom bearing groups such that an interchanging of any two groups leads to a stereoisomer.^[1] The most common stereocenters are chiral centers (such as asymmetric carbon atoms) and the double-bonded carbon atoms in cis-trans alkenes.

A chiral center consists of an atom holding a set of ligands (atoms or groups of atoms) in a spatial arrangement which is not superposable on its mirror image. A chiral center is a generalized extension of an asymmetric carbon atom, which is a carbon atom bonded to four different entities, such that an interchanging of any two groups gives rise to an enantiomer. ^[2] In organic chemistry a chiral center usually refers to a carbon, nitrogen, phosphorus, or sulfur atom, though it is also possible for other atoms to be chiral centers in organic and inorganic chemistry.

The term stereocenter was introduced in 1984 by Mislow and Siegel.^[3]

Possible number of stereoisomers

A molecule can have multiple stereocenters, giving it many stereoisomers. In compounds whose stereoisomerism is due to chiral centers, the total number of hypothetically possible stereoisomers will not exceed 2ⁿ, where n is the number of chiral centers. Molecules with symmetry frequently have fewer than the maximum possible number of stereoisomers.

Having two or more chiral centers may give a meso compound which is achiral. Meso compounds do not exhibit chirality due to the presence of an internal mirror plane of symmetry or a center of symmetry in the structure of the molecule in its most symmetric conformation. Planar chirality may also provide for chirality without having an actual chiral center present.

Chiral carbon

A chiral carbon or asymmetric carbon is a carbon atom which is asymmetric. Most chiral molecules have a chiral carbon, though the presence of a chiral carbon does not necessarily make a molecule chiral (see meso compound). A chiral carbon is often denoted by C*.

If the carbon is chiral, it follows that:

the carbon atom is sp³-hybridized;
there are four different groups attached to the carbon atom.

Almost any other configuration for the carbon would produce a center of symmetry. For example, an sp- or sp²-hybridized molecule would be planar, with a mirror plane. Two identical groups would give a mirror plane bisecting the molecule.

Other chiral centers

Chirality is not limited to carbon atoms, though carbon atoms are often centers of chirality due to their ubiquity in organic chemistry.

Nitrogen and phosphorus atoms are also tetrahedral. Racemization by Walden inversion may be restricted (such as ammonium or phosphonium cations), or slow. This allows the presence of chirality.

Metal atoms with tetrahedral or octahedral geometries may also be chiral due to having different ligands. For the octahedral case, several chiralities are possible. Having three ligands of two types, the ligands may be lined up along the meridian, giving the mer-isomer, or forming a face — the fac isomer. Having three bidentate ligands of only one type gives a propeller-type structure, with two different enantiomers denoted Λ and Δ.

References

^ Solomons & Fryhle. (2004). Organic Chemistry, 8th ed
^ IUPAC-definition of chirality center
^ Stereoisomerism and local chirality Kurt Mislow and Jay Siegel J. Am. Chem. Soc.; 1984; 106(11) pp 3319 - 3328; doi:10.1021/ja00323a043

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English Journal

An enantioselective organocatalyzed aza-Morita-Baylis-Hillman reaction of isatin-derived ketimines with acrolein.

Yoshida Y1, Sako M, Kishi K, Sasai H, Hatakeyama S, Takizawa S.
Organic & biomolecular chemistry.Org Biomol Chem.2015 Sep 14;13(34):9022-8. doi: 10.1039/c5ob00874c. Epub 2015 Jul 27.
A highly enantioselective aza-Morita-Baylis-Hillman (aza-MBH) reaction of isatin-derived ketimines with acrolein was established using β-isocupreidine (β-ICD) or α-isocupreine (α-ICPN) as a chiral acid-base organocatalyst. The present protocol readily furnished (S) or (R)-aza-MBH adducts with a
PMID 26214279

Evolution of a Unified Strategy for Complex Sesterterpenoids: Progress toward Astellatol and the Total Synthesis of (-)-Nitidasin.

Hog DT1,2, Huber FM1, Jiménez-Osés G3, Mayer P1, Houk KN4, Trauner D5.
Chemistry (Weinheim an der Bergstrasse, Germany).Chemistry.2015 Aug 20. doi: 10.1002/chem.201501423. [Epub ahead of print]
Astellatol and nitidasin belong to a subset of sesterterpenoids that share a sterically encumbered trans-hydrindane motif with an isopropyl substituent. In addition, these natural products feature intriguing polycyclic ring systems, posing significant challenges for chemical synthesis. Herein, the e
PMID 26300211

Forming Stereogenic Centers in Acyclic Systems from Alkynes.

Vabre R1, Island B1, Diehl CJ2, Schreiner PR2, Marek I3.
Angewandte Chemie (International ed. in English).Angew Chem Int Ed Engl.2015 Aug 17;54(34):9996-9. doi: 10.1002/anie.201504756. Epub 2015 Jun 30.
The combined carbometalation/zinc homologation followed by reactions with α-heterosubstituted aldehydes and imines proceed through a chair-like transition structure with the substituent of the incoming aldehyde residue preferentially occupying a pseudo-axial position to avoid the two gauche interac
PMID 26130570

Japanese Journal

Stereocontrolled synthesis of carbocyclic compounds with a quaternary carbon atom based on SN2 ' alkylation of γ,δ-epoxy-α,β-unsaturated ketones

Yoshimura Fumihiko,Kowata Ayano,Tanino Keiji
Organic & Biomolecular Chemistry 10(28), 5431-5442, 2012-07-28
… We developed a new method for stereoselective construction of an all-carbon quaternary stereogenic center on a carbocyclic ring based on regio- and stereoselective SN2' alkylation reactions of γ,δ-epoxy-α,β-unsaturated cyclic ketones. … For example, Eschenmoser-Claisen rearrangement of one of the substitution products resulted in stereoselective formation of a keto amide having contiguous quaternary and tertiary stereogenic centers. …
NAID 120005228736

面不斉遷移金属錯体の触媒的不斉合成

荒江祥永,小笠原正道
有機合成化学協会誌 70(6), 593-605, 2012-06-01
… Although "central chirality" based on stereogenic carbon atoms is arguably the most common chiral element in organic chemistry, chiral molecules devoid of stereogenic centers play important roles in stereoselective organic transformations. …
NAID 10030765844

Development of Atom-Economical Catalytic Asymmetric Reactions under Proton Transfer Conditions: Construction of Tetrasubstituted Stereogenic Centers and Their Application to Therapeutics

Kumagai Naoya
Chemical and Pharmaceutical Bulletin 59(1), 1-22, 2011
… The rare earth metal/amide-based ligand catalyst was successfully applied to catalytic asymmetric aminations, nitroaldol (Henry) reactions, Mannich-type reactions, and conjugate addition reactions, generating stereogenic tetrasubstituted centers. …
NAID 130000405482