of O sub 2 sub being a triplet oxygen triplet diradical in the ground state indicated as sup ... trapping of diradical intermediates Type I photooxygenation reactions are frequently used in the process of forming and trapping diradical species. Mirbach et al. reported on one such reaction in which an azo compound is lysed via Photodissociation photolysis to form the diradical hydrocarbon and then trapped ... more details
for benzyne is a cyclopentadiene . There are three possible diradical didehydrobenzenes 1,2 didehydrobenzene ... 106, 122, and 138 kcal mol 444, 510, and 577 kJ mol . ref name Bartlett The 1,4 diradical species has ... more details
because they proceed through a triplet state i.e., have a diradical mechanism, to which the Woodward ... 500X ref Quantum Chemistry Theoretical calculations found the 1,5 shift to be a diradical process, but without involving any diradical minima on the potential energy surface . ref Kless, A. Nendel, M ... more details
Chembox Watchedfields changed verifiedrevid 404979853 IUPACName Silylene SystematicName Silylidene Reference necessary date March 2011 OtherNames Hydrogen silicide II br Silicene br Section1 Chembox Identifiers PubChem 6327230 PubChem Ref Pubchemcite correct PubChem ChemSpiderID 4885758 ChemSpiderID Ref chemspidercite correct chemspider SMILES SiH2 StdInChI 1S H2Si h1H2 StdInChI Ref stdinchicite correct chemspider StdInChIKey XMIJDTGORVPYLW UHFFFAOYSA N StdInChIKey Ref stdinchicite correct chemspider Section2 Chembox Properties H 2 Si 1 ExactMass 29.992576597 g mol sup 1 sup Silylenes are chemical compound s containing a valence chemistry divalent silicon atom without any electrical charge . Both dicoordinate and tricoordinate silylenes are reported in the literature. They are considered to be heavier analogues of carbene . In earlier times, they were called Organosilicon silene , but this is a mistake, as that term means chemical compound compound s of covalent bond bond ed silicon Si C. The generic term analogous to carbene is silicene. Silylenes have been proposed as reactive intermediate s and are so unstable that they usually cannot be isolated. While carbene s are observed in either the triplet state triplet or singlet state depending on the nature of the substituents, silylenes typically have a diradical singlet ground state because the energy gap between the electron configuration 3s and electron configuration 3p electron configuration orbital s of the silicon atom is very large and so the singlet triplet gaps are enormous. History The first experimental chemical observation of silylene as an intermediate was demonstrated by P.S. Skell and E.J. Goldstein in 1964. The first stable silylene was synthesized and isolated as a diamino silylene, N,N di tert butyl 1,3 diaza 2 silacyclopent 4 en 2 ylidene N,N di tert butyl 1,3 diaza 2 silacyclopent 4 en 2 ylidene , in 1994 by Michael K. Denk M. Denk et al. ref name denk1 Denk, M., Green, J.C., Metzler, N., Wagner, ... more details
The Norrish reaction in organic chemistry describes the photochemical reaction s taking place with ketone s and aldehydes . This type of reaction is subdivided in Norrish type I reactions and Norrish type II reactions ref Named Organic Reactions , 2nd Edition, Thomas Laue and Andreas Plagens, John Wiley & Sons Chichester, England, New York, 2005 . 320 pp. ISBN 0 470 01041 X ref . The reaction is named after Ronald George Wreyford Norrish . Norrish I The Norrish type I reaction is the photochemical cleavage or homolysis of aldehydes and ketones into two free radical intermediates. The carbonyl group accepts a photon and is Photoexcitation excited to a photochemical Diradical singlet state . Through intersystem crossing the triplet state can be obtained. On cleavage of the carbon carbon bond from either state, two radical fragments are obtained. Image Norrish Radikal.png center 300px Norrish type I reaction Several secondary reaction modes are open to these fragments depending on the exact molecular structure. The fragments can simply recombine to the original carbonyl compound path A . By extrusion of carbon monoxide in path B, two organic residues can recombine with formation of a new carbon carbon bond When the carbon fragment has an hydrogen proton available it gets abstracted forming a ketene and a saturated hydrocarbon in path C When the alkyl fragment contains a proton it gets abstracted with formation of an aldehyde and an alkene . File Norrish1.png center 700px Norrish type I reaction The synthetic utility of this reaction type is limited. It often is a side reaction for instance in the Patern B chi reaction . One organic synthesis based on this reaction is that of bicyclohexylidene ref Bicyclohexylidene Nicholas J. Turro, Peter A. Leermakers, and George F. Vesley Organic Syntheses , Coll. Vol. 5, p.297 1973 Vol. 47, p.34 1967 http www.orgsynth.org orgsyn prep.asp?prep cv5p0297 Online article . ref . Norrish II A Norrish type II reaction is the photoch ... more details
Image MolybdenumMOdiagram.png thumb right 400px MO diagram of dimolybdenum A sextuple bond is a type of covalent bond involving 12 bonding electron s and in which the bond order is 6. The only known molecules with true sextuple bonds are the diatomic dimolybdenum molybdenum Mo sub 2 sub and ditungsten tungsten W sub 2 sub , which exist in the gaseous phase . There is strong evidence to believe that no two elements in the periodic table can form a bond with greater order than 6. ref name Roos Dimolybdenum and ditungsten Dimolybdenum Mo sub 2 sub can be observed in the gas phase at low temperatures 7K by a laser evaporation technique using molybdenum sheet with, for instance, near infrared spectroscopy or UV spectroscopy . ref cite journal title On the dimers of the VIB group a new NIR electronic state of Mo sub 2 sub author D. Kraus, M. Lorenz and V. E. Bondybey journal PhysChemComm year 2001 volume 4 pages 44 48 doi 10.1039 b104063b issue 10 ref Like dichromium, a diradical singlet state is expected from dimolybdenum. ref cite journal title The Many Ways To Have a Quintuple Bond author Gabriel Merino, Kelling J. Donald, Jason S. D Acchioli, and Roald Hoffmann journal J. Am. Chem. Soc. year 2007 volume 129 issue 49 pages 15295 15302 doi 10.1021 ja075454b pmid 18004851 ref Higher bond order is reflected in shorter bond length of 194 pm. Other molecules Although diatomic chromium Cr sub 2 sub and uranium U sub 2 sub have formal structures with twelve electron bonds, their effective bond orders derived from quantum chemistry calculations are less than 5 which would be quintuple bond s . ref name Roos cite journal last Roos first Bj rn O. coauthors Antonio C. Borin, and Laura Gagliardi year 2007 title Reaching the Maximum Multiplicity of the Covalent Chemical Bond journal Angewandte Chemie International Edition doi 10.1002 anie.200603600 volume 46 pages 1469 pmid 17225237 issue 9 ref References Reflist See also refbegin cite journal doi 10.1021 ja00540a034 title Dim ... more details
dablink Not to be confused with carbine . File Carbene.png thumb 60px Methylene carbene In chemistry , a carbene is a molecule containing a neutral carbon atom with a Valence chemistry valence of two and two unshared valence electron s. The general formula is RR C , but the carbon can instead be double bonded to one group. The term carbene may also merely refer to the compound H sub 2 sub C , also called methylene , the parent hydride to which all other carbene compounds are related. ref Cite book title Molecular Orbitals of Transition Metal Complexes isbn 0198530935 page 7 last Hoffmann first Roald authorlink Roald Hoffmann publisher Oxford year 2005 postscript None ref ref GoldBookRef title carbenes file C00806 ref Carbenes are classified as either singlet state singlets or triplet state triplets depending upon their electronic structure. Most carbenes are very short lived, although persistent carbene s are known. One well studied carbene is Cl sub 2 sub C , or dichlorocarbene , which can be generated in situ from chloroform and a strong base chemistry base . Structure and bonding Image carbenes.png frame right Singlet and triplet carbenes The two classes of carbenes are Diradical singlet and diradical triplet carbenes. Singlet carbenes are spin paired. In the language of valence bond theory , the molecule adopts an sp sup 2 sup Orbital hybridisation hybrid structure . Triplet carbenes have two unpaired electrons. They may be either linear or bent, i.e. sp or sp sup 2 sup hybridized, respectively. Most carbenes have a nonlinear triplet ground state, except for those with nitrogen, oxygen, or sulfur atoms, and halides directly bonded to the divalent carbon. Carbenes are called singlet or triplet depending on the electronic spin physics spins they possess. Triplet carbenes are paramagnetic and may be observed by electron spin resonance spectroscopy if they persist long enough. The total spin of singlet carbenes is zero while that of triplet carbenes is one in units ... more details
Two Photon Absorption of Singlet Diradical Hydrocarbons Kenji Kamada, Koji Ohta, TakashiKubo,Akihiro ... ref a diradical resonance contribution for the compound depicted below was also linked to efficient ... GM. Image DiradicalApplicationinTPA.png 300px Diradical Application in TPA TPA Coefficients The two ... more details
For the ICAO airport code see Candle Lake Airpark , for the diradical compound see Dichlorocarbene . PBB geneid 6347 Chemokine C C motif ligand 2 CCL2 also known as monocyte chemotactic protein 1 MCP 1 or small inducible cytokine A2 is a protein that in humans is encoded by the CCL2 gene . CCL2 is a small cytokine belonging to the CC chemokine family. CCL2 recruits monocyte s, memory T cells , and dendritic cells to sites of tissue injury, infection , and inflammation . ref name pmid8170963 pmid 8170963 ref ref name pmid8830793 pmid 8830793 ref Genomics As with many other CC chemokines, CCL2 is located on chromosome 17 17q11.2 q21.1 in humans. ref name pmid2004761 pmid 2004761 ref The gene spans 1,927 bases and lies on the Watson plus strand. The gene has three exon s and two intron s. It is produced as a protein precursor containing signal peptide of 23 amino acid s and a mature peptide of 76 amino acids. ref name pmid2465924 pmid 2465924 ref ref name pmid2923622 pmid 2923622 ref The predicted weight is 11.025 kiloDaltons kDa . In the mouse the homolog is Sig je. Population genetics The levels of this protein vary considerably between normal people. Multivariable adjusted heritability of CCL2 concentrations in whites of European descent has been reported to be 0.37 in plasma and 0.44 in serum ref name McDermott2005 pmid 16116069 ref ref name Bielinski2007 pmid 17917677 ref Molecular biology It is a monomeric polypeptide , with a molecular weight of approximately 13kDa. It is tethered on endothelial cells by glycosaminoglycan side chains of proteoglycans. It is primarily secreted by monocyte s, macrophage s and dendritic cell s. It is a platelet derived growth factor inducible gene. It is cleaved by the metalloproteinase MMP 12. The cell surface receptors that bind CCL2 are CC chemokine receptors CCR2 CCR2 and CC chemokine receptors CCR4 CCR4 . ref name pmid17160712 pmid 17160712 ref This cytokine displays chemotactic activity for monocytes and basophils but not for neutrophils ... more details
Chembox ImageFile Disilyne.svg ImageSize 244 ImageName Structural formula of disilyne IUPACName Disilyne OtherNames Disilyn Section1 Chembox Identifiers CASNo 36835 58 2 ChemSpiderID 16341537 ChemSpiderID Ref Chemspidercite SMILES SiH SiH StdInChI 1S H2Si2 c1 2 h1 2H StdInChIKey NWEREQWWNYLPTF UHFFFAOYSA N Section2 Chembox Properties H 2 Si 2 ExactMass 57.969503130 g mol sup 1 sup Section3 Chembox Related Function silyls OtherFunctn Silylene br Trimethylsilyl A disilyne is a chemical compound that contains a formal silicon silicon triple bond and as such is formulated R sub 2 sub Si sub 2 sub where R is a substituent group and is the silicon analogue of an alkyne . The hypothetical parent hydride, Si sub 2 sub H sub 2 sub does not actually exist, and all attempts to synthesize it result in a diradical disilene , with the systematic name of disilene 1,2 diyl. This compound readily tautomerises to disilenylidene. Some chemists use the term silyne to refer to compounds containing a silicon silicon triple bond ref name Wiberg&Holleman Egon Wiberg, Arnold Frederick Holleman 2001 Inorganic Chemistry , Elsevier ISBN 0 12 352651 5 ref whilst others ref cite journal title The quest for a stable silyne, RSi CR . The effect of bulky substituents 1 author Miriam Karni, Yitzhak Apeloig journal Silicon Chemistry month January year 2002 volume 1 issue 1 pages 59 65 doi 10.1023 A 1016091614005 ref use the term to refer to compounds containing a silicon carbon triple bond by analogy to silene which often refers to compounds containing silicon carbon double bonds. ref Greenwood&Earnshaw ref The term polysilyne can refer to the layer polymer SiH sub n sub or substituted derivatives. ref name Wiberg&Holleman The first reported disilynes Image Sekiguchi silyne from xtal 3D balls.png thumb right The structure of the first disilyne characterised The first example isolated and characterised by X ray crystallography is an emerald green crystalline compound reported in 2004. ref cite journal ... more details
Carbene analogs in chemistry are carbenes with the carbon atom replaced by another chemical element . Just as regular carbenes they appear in chemical reactions as reactive intermediates and with special precautions they can be stabilized and isolated as chemical compounds. Carbenes have some practical utility in organic synthesis but carbene analogs are mostly laboratory curiosities only investigated in academia. Carbene analogs are known for elements of group 13 elements group 13 , group 14 elements group 14 , group 15 elements group 15 and group 16 elements group 16 . Group 13 carbene analogs In group 13 elements the boron carbene analog is called a boranylidene . Group 14 carbene analogs The heavier group 14 element group 14 carbenes are silylene s, R sub 2 sub Si , germylenes R sub 2 sub Ge , stannylenes R sub 2 sub Sn and plumbylenes R sub 2 sub Pb , collectively known as metallylenes and regarded as monomer s for polymetallane s ref Stable Heavier Carbene Analogues Yoshiyuki Mizuhata, Takahiro Sasamori, and Norihiro Tokitoh Chem. Rev. 2009 , 109, 3479 3511 DOI 10.1021 cr900093s ref . The oxidation state for these compounds is 2 and stability increases with principal quantum number moving down a row in the periodic table . This makes dichloroplumbylene PbCl sub 2 sub and dichlorostannylene SnCl sub 2 sub stable ionic compound s although they exist as polymers or ion pairs. Group 14 carbene analogs do not form orbital hybridization hybrid orbitals but instead retain ns sup 2 sup np sup 2 sup electron configuration due to the increasing s p gap for larger elements. Two electrons remain in an s orbital and therefore their compounds have exclusively Diradical singlet ground states and not the triplet ground state which can be observed in carbenes depending on the substituents. The s orbital lone pair is inert and the vacant p orbital is very reactive. Stable group 14 carbenes require stabilization of this p orbital which is usually accomplished by coordination of ... more details
diboron is a diradical and since the spins are parallel the compound is paramagnetic . Image MO diagram ... is a paramagnetic diradical . When both HOMO electrons pair up with opposite spins in one orbital ... more details
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