Distinguish biradical A diradical in organic chemistry is a molecule molecular species with two electron s occupying two Degenerate energy level degenerate molecular orbital s MO . ref Gold Book definition http goldbook.iupac.org D01765.html diradicals http www.iupac.org goldbook D01765.pdf PDF ref ref The triplet state . Turro, Nicholas J. J. Chem. Educ. 1969 , 46, 2. ref They are known by their higher reactivities and shorter lifetimes. In a broader definition diradicals are even electron molecules that have one bond less than the number permitted by the standard rules of valence. ref S. Pedersen J. L. Herek A. H. Zewail, Science 1994 , 266, 1359 ref ref A. H. Zewail, Angew. Chem., Int. Ed. 2000 , 39, 2586 ref The electrons can pair up with opposite spin physics spin in one MO leaving the other empty. This is called a singlet state . Alternatively each electron can occupy one MO with spins parallel to each other. This is called a triplet state . The related radical chemistry radical has just one free electron. The phrases singlet and triplet are derived from the appearance of diradicals in electron spin resonance a singlet diradical displays a single peak in its spectrum and a triplet has its peak split into a central peak with two adjacent peaks. The triplet state has total spin quantum number S 1 and is paramagnetic . ref Gold Book definition http goldbook.iupac.org T06503.html triplet state http www.iupac.org goldbook T06503.pdf PDF ref The singlet state has S 0 and is diamagnetic . The degeneracy of each state can be found with Hund s rule of maximum multiplicity 2S 1. In molecules the free electrons can reside on one atom or on different atoms. A molecule can have a singlet state or triplet state with different energy and both states can inter convert by a process called intersystem crossing . Phosphorescence is based on this principle. Discrete molecules with a diradical ... http www.meta synthesis.com webbook 16 diradical diradical.html Link References reflist Category ... more details
Orphan date January 2011 In chemistry , carbonite CO sub 2 sub sup 2 sup would be a diradical polyatomic ion polyatomic anion , with the IUPAC name dioxidomethylidene . Because it is a diradical, it is unlikely to exist in solution as it will be oxidised on contact with water to carbonic acid. The heat from the reaction will likely decompose the carbonic acid to water and carbon dioxide. The hypothetical presence of carbonite ions can be used to explain the mechanics of carbon monoxide absorption on ceria . ref name Binet 1994 cite journal last Binet first Claude coauthors Ahmed Badri, Magali Boutonnet Kizling and Jean Claude Lavalley title FTIR study of carbon monoxide adsorption on ceria CO2 2 carbonite dianion adsorbed species journal Journal of the Chemical Society, Faraday Transactions year 1994 volume 90 pages 1023 1028 doi 10.1039 FT9949001023 ref References Reflist Category Anions physical chemistry stub ... more details
In quantum mechanics , spin multiplicity indicates the number of possible quantum states of a system with given principal spin physics spin quantum number S. The different states are distinguished by the spin projection quantum number S sub z sub , which can take the values S, S 1, ..., S 1, S. Therefore, the multiplicity is 2S 1, where S is the number of singly occupied electrons multiplied by the Electron Spin Quantum Number, m sub s sub . A system with S 0 has exactly one possible state it is therefore in a singlet state . A system with S 1 2 is a doublet state doublet S 1 is a triplet state triplet , and so on. The most important application is to electrons. A single electron as in a free radical has S 1 2 it is therefore always in a doublet state. Two electrons as in a diradical can pair up in a singlet or in a triplet state. Normally the singlet is the ground state . For example, oxygen has two singly occupied electrons which could have spin multiplicity of 3. This means that the spins could be up up or up down or down down, total 3 possibilities. Using the formula, Spin Multiplicity of oxygen 2S 1 2 2 1 2 1 3, where S two singly occupied electrons m sub s sub . m sub s sub always equal to 1 2, proven by Otto Stern and Walther Gerlach in 1924 Category Quantum mechanics it Molteplicit di spin ... more details
The Cope rearrangement is an extensively studied organic reaction involving the sigmatropic rearrangement 3,3 sigmatropic rearrangement of 1,5 dienes ref Arthur C. Cope et al. J. Am. Chem. Soc. 1940 , 62 , 441. ref ref Rhoads, S. J. Raulins, N. R. Org. React. 1975 , 22 , 1 252. Review ref ref Hill, R. K. Comp. Org. Syn. 1991 , 5 , 785 826. ref ref Wilson, S. R. Org. React. 1993 , 43 , 93 250. Review ref . It was developed by Arthur C. Cope . For example 3 methyl 1,5 hexadiene heated to 300 C yields 1,5 heptadiene. Image Cope Rearrangement Scheme.png center 400px The Cope rearrangement of 3 methyl 1,5 hexadiene The Cope rearrangement causes the Fluxional molecule fluxional states of the molecules in the bullvalene family. Mechanism Although the Cope rearrangement is concerted reaction concerted and pericyclic , it can also be considered to go via a transition state that is energetically and structurally equivalent to a radical chemistry diradical . This is an alternative explanation which remains faithful to the uncharged nature of the Cope transition state, while preserving the principles of orbital symmetry. This also explains the high energy requirement to perform a Cope rearrangement. Although illustrated in the chair conformation , the Cope can also occur with cyclohexadienes in the boat conformation. Image Cope.png The above description of the transition state is not quite correct. It is currently generally accepted that the Cope rearrangment follows an allowed concerted route through a homoaromatic transition state and not a diradical. That is unless the potential energy surface is perturbed to favor the diradical. ref Williams, R. V., Chem. Rev. 2001, 101 5 , 1185 1204. ref Examples The rearrangement is widely used in organic synthesis. It is symmetry allowed when it is suprafacial on all components. The transition state of the molecule passes through a boat or chair like transition state. An example of the Cope rearrangement is the expansion of a cyclobutane ... more details
The Hunsdiecker reaction also called the Borodin reaction after Alexander Borodin is the organic reaction of silver salts of carboxylic acid s with halogen s to give organic halide s. ref Cl re Hunsdiecker , et al. U.S. Patent 2,176,181. ref ref cite journal author Heinz Hunsdiecker Cl re Hunsdiecker journal Chemische Berichte Ber. year 1942 volume 75 pages 291 doi 10.1002 cber.19420750309 title ber den Abbau der Salze aliphatischer S uren durch Brom ref ref cite journal author Alexander Borodin Borodin, A. journal Ann. year 1861 volume 119 pages 121 doi 10.1002 jlac.18611190113 title Ueber Bromvalerians ure und Brombutters ure ref ref OrgSynth title Methyl 5 bromovalerate author Allen, C. F. H. Wilson, C. V. collvol 3 collvolpages 578 year 1955 prep cv3p0578 ref It is an example of a halogenation reaction. The reaction is named after Heinz Hunsdiecker and Cl re Hunsdiecker . Image Hunsdiecker Reaction Scheme.png 300px The Hunsdiecker reaction Several reviews have been published. ref name Johnson1956 cite journal author Johnson, R. G. Ingham, R. K. journal Chem. Rev. year 1956 volume 56 pages 219 doi 10.1021 cr50008a002 title The Degradation of Carboxylic Acid Salts by Means of Halogen the Hunsdiecker Reaction ref ref Wilson, C. V. Org. React. 1957 , 9 , 341. Review ref Mercuric oxide will also effect this transformation. ref OrgSynth title Bromocyclopropane author Meek, J. S. Osuga, D. T. collvol 5 collvolpages 126 year 1973 prep cv5p0126 ref ref OrgSynth title Mercury II oxide modified Hunsdiecker reaction 1 Bromo 3 chlorocyclobutane author Lampman, G. M. Aumiller, J. C. collvol 6 collvolpages 179 year 1988 prep cv6p0179 ref Reaction mechanism The reaction mechanism of the Hunsdiecker reaction is believed to involve Radical chemistry organic radical intermediates. The silver salt of the carboxylic acid 1 will quickly react with bromine to form intermediate 2 . Formation of the diradical pair 3 allows for radical decarboxylation to form the diradical pair 4 , whic ... more details
Cleanup date November 2010 reason Open shell seems to be not a common term In the context of atomic orbitals , an open shell is a valence shell which is not completely filled with electrons or that has not given all of its valence electrons through chemical bond s with other atoms or molecules during a chemical reaction. Atoms generally reach a noble gas configuration in a molecule. The noble gases Helium He , Neon Ne , Argon Ar , Krypton Kr , Xenon Xe , Radon Rn are not reactive and have configurations 1s sup 2 sup He , 1s sup 2 sup 2s sup 2 sup 2p sup 6 sup Ne , 1s sup 2 sup 2s sup 2 sup 2p sup 6 sup 3s sup 2 sup 3p sup 6 sup Ar , etc. For molecules it signifies that there are unpaired electron s. In molecular orbital theory, this leads to molecular orbitals that are singly occupied. In computational chemistry implementations of molecular orbital theory, open shell molecules have to be handled by either the restricted Open shell Hartree Fock method or the unrestricted Hartree Fock method. Likewise a closed shell or closed shell configuration is obtained with a completely filled valence shell. This configuration is very stable. ref http www.newi.ac.uk buckleyc periodic.htm Periodic table ref In another meaning a closed shell configuration corresponds to state with all molecular orbital s doubly occupied or empty a diradical singlet state . ref http www.semichem.com ampacmanual ci.html Configuration Interaction Bot generated title ref See also Periodic table electron configurations Octet rule Valence shell Free radical References Reflist 3. http iopenshell.usc.edu iOpenShell Center for computational studies of open shell and electronically excited species Category Atomic physics Category Chemical bonding Category Quantum chemistry Category Theoretical chemistry Category Computational chemistry ar pt N vel aberto ... more details
File Calicheamicin.png thumb right 250px Calicheamicin Enediynes are a class of bacterial natural product s characterized by either nine and ten membered rings containing two triple bond s separated by a double bond . ref cite journal doi 10.1073 pnas.90.13.5881 journal PNAS year 1993 volume 90 issue 13 pages 5881 5888 title Chemistry and biology of natural and designed enediynes author K. C. Nicolaou A. L. Smith E. W. Yue pmid 8327459 pmc 46830 ref Many of these compounds are capable to undergo the Bergman cyclization . The resulting Radical chemistry diradical , a 1,4 dehydrobenzene derivative, is capable of abstracting hydrogen atoms from the sugar backbone of DNA which results in strand scission. ref cite journal author S. Walker R. Landovitz W.D. Ding G.A. Ellestad D. Kahne title Cleavage behavior of calicheamicin 1 and calicheamicin T journal Proc Natl Acad Sci U.S.A. year 1992 volume 89 issue 10 pages 4608 12 pmc 49132 pmid 1584797 doi 10.1073 pnas.89.10.4608 ref This high reactivity with DNA makes the substances toxic. They are being researched as antitumor agents. Several of the naturally occurring enediynes have entered clinical trials against cancer ref http www.ingentaconnect.com content ben fmc 2004 00000001 00000001 art00011 Designed Enediyne Antitumor Agents ref ref http www.chem.uga.edu vpopik Enediynes.html Development of Photoswitchable Enediyne Antibiotics ref and in Japan neocarzinostatin is used clinically. Three classes of enediynes exist Calicheamicin esperamicin Dynemicin Chromoprotein types The enediyne group in those compounds is often called a warhead. References Reflist Category Antibiotics Category Cancer research Category Enediynes Category Functional groups de Endiine zh ... more details
Phosphinidenes also phosphanylidenes in chemistry are chemical compounds containing a monovalent and diradical phosphorus atom. They are the phosphorus analogs of carbene s and nitrene s. The parent compound is phosphinidene HP ref cite DOI 10.1002 anie.200905689 ref . This type of compound is very reactive and has only been observed in the gas phase and at cryogenic temperatures. Terminal transition metal complexed phosphinidenes L sub n sub M P R are phosphorus analogs of transition metal carbene complexes where L is a spectator ligand . Two isolable representatives of this group are OC sub 5 sub W P Ph ref cite DOI 10.1021 ja00380a029 ref and Cp sub 2 sub W P Mes ref cite DOI 10.1039 C39870001282 ref . In this type of compound the M P bond is a true double bond with strength increasing going down a row in the transition metal group. In clusters More common than complexes of terminal phosphinidine ligands are cluster compound s wherein the phophinidene is a triply and less commonly doubly bridging ligand . One example is the ter butylphosphinidene complex t BuP Fe sub 3 sub CO sub 10 sub . ref Gottfried Huttner, Konrad Knoll RP Bridged Metal Carbonyl Clusters Synthesis, Properties, and Reactions Angewandte Chemie International Edition in English 1987, Volume 26, 743 760. DOI 10.1002 anie.198707431 ref In clusters, phosphinidene is electronically similar to sulfide. See also Carbene analog References Reflist Category Reactive intermediates Category Phosphorus compounds ... more details
chembox ImageFile Benzvalene.svg ImageSize IUPACName tricyclo 3.1.0.0 sup 2,6 sup hex 3 ene OtherNames Section1 Chembox Identifiers CAS CAS 6 5 9 8 5 8 PubChem 136470 chEBI SMILES C1 CC2C3C1C23 InChI 1 C6H6 c1 2 4 5 3 1 6 4 5 h1 6H Section2 Chembox Properties Formula C sub 6 sub H sub 6 sub MolarMass 78.1 g mol Appearance Density MeltingPt BoilingPt Solubility Section3 Chembox Hazards MainHazards FlashPt Autoignition Benzvalene is an organic compound and one of several isomer s of benzene . ref cite DOI 10.1002 anie.198105291 ref . It was synthesised in 1971 by Thomas J. Katz et al. ref cite DOI 10.1021 ja00744a045 ref ref cite DOI 10.1021 jo990883g ref The 1971 synthesis consisted of treating cyclopentadiene with methyllithium in dimethylether and then with dichloromethane and methyllithium in at 45 C. The hydrocarbon in solution was described as having an extraordinary foul odor. Due to the high steric strain present in benzvalene, the pure compound easily detonates, for example by scratching. The compound converts to benzene with a chemical half life of approximately 10 days. This symmetry forbidden transition is believed to take place through a diradical intermediate ref Rearrangements and interconversions of compounds of the formula CH n Lawrence T. Scott, Maitland. Jones Chem. Rev. , 1972, 72 2 , pp 181 202 DOI 10.1021 cr60276a004 ref Polybenzvalene Benzvalene can be polymerized in a Ring opening metathesis polymerisation ROMP process to polybenzvalene ref cite DOI 10.1021 ja00217a049 ref . This polymer contains highly strained bicyclobutane rings which again makes it a sensitive material. The rings can be isomerization isomerized to 1,3 dienes and for this reason polybenzvalene has been investigated as a precursor to polyacetylene . References Reflist Category Alkenes de Benzvalen fr Benzval ne it Benzvalene nl Benzvaleen zh ... more details
the triplet diradical . Spin inversion to the singlet diradical allows closure to the cyclobutane ... difficulty of 2 2 photocycloadditions is the possibility of side reactions associated with the diradical ... more details
See also Methylenes Uncategorized date January 2011 Chembox ImageFile Carbene.png ImageSize 25px IUPACName Methylene OtherNames Carbene br Methylidene Section1 Chembox Identifiers CASNo 2465 56 7 CASNo Ref cascite correct ?? PubChem 123164 PubChem Ref Pubchemcite correct PubChem ChemSpiderID 109779 ChemSpiderID Ref chemspidercite correct chemspider MeSHName Carbene ChEBI 51376 Beilstein 1696832 Gmelin 56 SMILES CH2 StdInChI 1S CH2 h1H2 StdInChI Ref stdinchicite correct chemspider StdInChIKey HZVOZRGWRWCICA UHFFFAOYSA N StdInChIKey Ref stdinchicite correct chemspider Section2 Chembox Properties C 1 H 2 ExactMass 14.015650064 g mol sup 1 sup Methylene is a carbene encountered in organic chemistry . ref Cite book title Molecular Orbitals of Transition Metal Complexes id ISBN 0198530935 page 7 last Hoffmann first Roald publisher Oxford year 2005 postscript None ref ref GoldBookRef title carbenes file C00806 ref Methylene has a non linear triplet ground state, and is thus paramagnetic, it is stable in the gaseous state. Methylene can be considered to be a diradical, addition reactions are very fast and exothermic. Methylene tends to dimerize at high concentrations into ethene . ref name isbn0 8493 5387 4 cite book author Laz r, Milan Lazr , Milan title Free radicals in chemistry and biology publisher CRC Press location Boca Raton year 1989 pages isbn 0 8493 5387 4 oclc doi accessdate ref References reflist 2 Hydrocarbon stub bs Metilen cs Methylen de Methylengruppe es Metileno fr M thyl ne io Metileno id Metilena it Metilene he hu Metil n ja pt Metileno ru sr Metilen sv Metylengrupp zh ... more details
. In 1966 Paul Dowd determined with electron spin resonance that this compound also has a diradical ... Oxyallyl In the oxyallyl diradical OXA one methylene group in TMM is replaced by oxygen. This reactive ... of the Oxyallyl Diradical Takatoshi Ichino, Stephanie M. Villano, Adam J. Gianola, Daniel J. Goebbert ... molecules, and therefore the relative stability of the diradical singlet ground state to the triplet ... more details
Chembox verifiedrevid 399367733 ImageFileL1 Acetolactone 2D.png ImageNameL1 Structural formula ImageFileR1 Acetolactone 3D balls B.png ImageNameR1 Ball and stick model IUPACName oxiran 2 one OtherNames Section1 Chembox Identifiers ChemSpiderID Ref chemspidercite correct chemspider ChemSpiderID 393042 InChI 1 C2H2O2 c3 2 1 4 2 h1H2 InChIKey HZSIFDFXFAXICF UHFFFAOYAQ SMILES1 O C1OC1 StdInChI Ref stdinchicite correct chemspider StdInChI 1S C2H2O2 c3 2 1 4 2 h1H2 StdInChIKey Ref stdinchicite correct chemspider StdInChIKey HZSIFDFXFAXICF UHFFFAOYSA N CASNo 42879 41 4 PubChem SMILES O C1CO1 Section2 Chembox Properties Formula C sub 2 sub H sub 2 sub O sub 2 sub MolarMass 58.04 g mol sup 1 sup Appearance Density MeltingPt BoilingPt Solubility Section3 Chembox Hazards MainHazards FlashPt Autoignition Acetolactone or acetolactone is a organic compound with formula C sub 2 sub H sub 2 sub O sub 2 sub . It is the smallest member of the lactone family but can also be described as the epoxide of ketene . The compound was described in 1997 as a transient species in mass spectrometry experiments. ref Detlef Schr der, Norman Goldberg, Waltraud Zummack, Helmut Schwarz , John C. Poutsma and Robert R. Squires 1997 , Generation of acetolactone and the acetoxyl diradical CH2COO in the gas phase . International Journal of Mass Spectrometry and Ion Processes, Volumes 165 166, November issue, Pages 71 82. doi 10.1016 S0168 1176 97 00150 X ref Although acetolactone itself has not been isolated in bulk, the related species bis trifluromethyl acetolactone CF sub 3 sub sub 2 sub C sub 2 sub O sub 2 sub , which enjoys a degree of electronic stabilisation from its two trifluoromethyl groups, is known and has a half life of 8 h at 25 C. This compound is prepared by photolysis of bis trifluromethyl malonyl peroxide. ref Waldemar Adam, Ju Chao Liu, Oswaldo Rodriguez 1973 , Bis trifluoromethyl acetolactone, a Stable Lactone . J. Org. Chem., Volume 38, pages 2269 2270. DOI 10.1021 jo0 ... more details
File Isocyanide resonance.svg thumb 280px Example of a dipolar compound, represented by a Resonance chemistry resonance structure isocyanide In organic chemistry , a dipolar compound or simply dipole is an electrically neutral molecule carrying a positive and a negative charge in at least one canonical description. In most dipolar compounds the charges are Delocalized electron delocalized . ref name dipolar compounds GoldBookRef title dipolar compounds file D01753 ref Unlike Salt chemistry salt s, dipolar compounds have charges on separate atoms, not on positive and negative ion s which make up the compound. Dipolar compounds exhibit a Dipole Molecular dipoles dipole moment . Dipolar compounds can be represented by a Resonance chemistry resonance structure . Contributing structures containing charged atoms are denoted as zwitterions . ref Braida et al. http www.ncbi.nlm.nih.gov pubmed 20481497 A clear correlation between the diradical character of 1,3 dipoles and their reactivity toward ethylene or acetylene. J. Am. Chem. Soc. 2010 Jun 9 132 22 7631 7 ref ref Hartmann and Heuschmann http onlinelibrary.wiley.com doi 10.1002 anie.198912671 abstract Isolation of a Zwitterion in a Diels Alder Reaction with Inverse Electron Demand Angewandte Chemie september 1989 Volume 28, Issue 9, pages 1267 1268 ref ref name Takahisa cite journal last1 MacHiguchi first1 Takahisa last2 Okamoto first2 Junko last3 Takachi first3 Junpei last4 Hasegawa first4 Toshio last5 Yamabe first5 Shinichi last6 Minato first6 Tsutomu title Exclusive Formation of Methyleneoxetanes in Ketene Alkene Cycloadditions. Evidence for Intervention of Both an Methyleneoxetane and the Subsequent 1,4 Zwitterion journal Journal of the American Chemical Society volume 125 issue 47 pages 14446 year 2003 pmid 14624592 doi 10.1021 ja030191g ref ref name PIN IUPAC http old.iupac.org reports provisional abstract04 BB prs310305 Chapter7.pdf Preferred International Union of Pure and Applied Chemistry IUPAC Names Chapte ... more details
Diradical s are molecules containing two radical centers. Multiple radical centers can exist in a molecule. Atmospheric oxygen naturally exists as a diradical in its ground state as triplet oxygen . The high reactivity of atmospheric oxygen is due to its diradical state. Interestingly, non radical states of dioxygen are actually less stable. The relative stability of the oxygen diradical is primarily .... The diradical state of oxygen also results in its paramagnetic character, which is demonstrated ... . The oxygen molecule is a stable diradical , best represented by O O , which is stable because ... spin unpaired Triplet oxygen triplet diradical, but an extremely reactive spin paired Singlet oxygen ... more details
The Bergman cyclization or Bergman reaction or Bergman cycloaromatization is an organic reaction and more specifically a rearrangement reaction taking place when an enediyne is heated in presence of a suitable hydrogen donor Scheme 1 ref p Benzyne. Generation as an intermediate in a thermal isomerization reaction and trapping evidence for the 1,4 benzenediyl structure Richard R. Jones, Robert G. Bergman J. Am. Chem. Soc. 1972 94 2 660 661. http pubs.acs.org cgi bin abstract.cgi jacsat 1972 94 i02 f pdf f ja00757a071.pdf Abstract ref . It is named for the American chemist Robert George Bergman b. 1942 . The reaction product is a derivative of benzene . Image Bergman cyclization revised.png 500px center Scheme 1. Bergman cyclization The reaction proceeds by a thermal reaction or pyrolysis above 200 C forming a short lived and very reactive para benzyne biradical species. It will react with any hydrogen donor such as 1,4 cyclohexadiene which converts to benzene. When quenched by tetrachloromethane the reaction product is a 1,4 dichlorobenzene and with methanol the reaction product is benzyl alcohol . When the enyne moiety is incorporated into a 10 membered hydrocarbon ring e.g. cyclodeca 3 ene 1,5 diyne in scheme 2 the reaction, taking advantage of increased ring strain in the reactant, is possible at the much lower temperature of 37 C. Image Bergman ring.png 450px center Scheme 2. Bergman reaction of cyclodeca 3 ene 1,5 diyne Naturally occurring compounds such as calicheamicin contain the same 10 membered ring and are found to be cytotoxic . These compounds generate the diradical intermediate described above which can cause single and double stranded DNA cuts. There are novel drug s which attempt to make use of this property, including monoclonal antibodies such as mylotarg ref Design and synthesis of heterocycle fused enediyne prodrugs activable at will Luca Banfi, Andrea Basso, Giuseppe Guanti, and Renata Riva Arkivoc 2006 HL 1786GR 261 275 http www.arkat usa.org ar ... more details
Encyclopedia
top
