| 词条 | Fluorenylidene |
| 释义 |
| ImageFile = Fluorenylidene Carbene.png | ImageSize = | IUPACName = fluorene | OtherNames = |Section1={{Chembox Identifiers | CASNo = | PubChem = | ChemSpiderID = 10617870 | SMILES = c1ccc-2c(c1)[C]c3c2cccc3 | InChI = 1/C13H8/c1-3-7-12-10(5-1)9-11-6-2-4-8-13(11)12/h1-8H | InChIKey = LJJQENSFXLXPIV-UHFFFAOYAV | StdInChI = 1S/C13H8/c1-3-7-12-10(5-1)9-11-6-2-4-8-13(11)12/h1-8H | StdInChIKey = LJJQENSFXLXPIV-UHFFFAOYSA-N |Section2={{Chembox Properties | C=13 | H=8 | Appearance = | Density = | MeltingPt = | BoilingPt = | Solubility = |Section3={{Chembox Hazards | MainHazards = | FlashPt = | AutoignitionPt = }} 9-Fluorenylidene is an aryl carbene derived from the bridging methylene group of fluorene. Fluorenylidene has the unusual property that the triplet ground state is only 1.1 kcal/mol (4.6 kJ/mol) lower in energy than the singlet state.[1] For this reason, fluorenylidene has been studied extensively in organic chemistry. Fluorenylidene is a reactive intermediate. Reactions involving fluorenylidene proceed through either the triplet or singlet state carbene, and the products formed depend on the relative concentration of spin states in solution, as influenced by experimental conditions.[2] The rate of intersystem crossing is determined by the temperature and concentration of specific spin-trapping agents.[1] StructureThe ground state is believed to be a bent triplet, with two orthogonal sp hybrid orbitals singly occupied by unpaired spins.[3][4] One electron occupies an orbital of sigma symmetry in the plane of the rings, while the other occupies an orbital of pi symmetry, which interacts with the pi systems of the adjacent aromatic rings (delocalization into the rings is minimal, since zero-field parameter D is high).[5] The zero field splitting parameters predict a bond angle greater than 135°, and since the ideal bond geometry for cyclopentane carbons is about 109°, considerable ring strain causes the methylene sigma bonds to be bent.[5] In the singlet state, the spin-paired electrons occupy the sp2 hybrid orbital, orthogonal to an empty p-orbital.[6] Conversion of singlet to triplet fluorenylidene is achieved through intersystem crossing (ISC). Generation of FluorenylideneFluorenylidene can be produced by photolysis of 9-diazofluorene (DAF). Ultra-fast (300 fs) time resolved laser-flash photolysis of DAF implicates a four-step process in the formation of fluorenylidene by irradiation of 9-diazofluorene.[7]
Reaction of Fluorenylidene in SolutionFluorenylidene reacts with olefins as predicted by the Skell-Woodworth rules.[8] The stereochemistry of cycloaddition products depends on the relative rates of cyclopropanation (or other reactions) and intersystem crossing.[9] Stabilization of specific spin states, and, by extension, increased stereospecificity can be achieved by using solvents of different polarities . Triplet Fluorenylidene ReactivityTriplet fluorenylidene reacts with olefins in a stepwise fashion to produce a racemic mixture, provided that the rate of spin inversion (intersystem crossing) is not significantly faster than rates of intermediate bond rotation.[9] Singlet Fluorenylidene ReactivitySinglet fluorenylidene reacts with olefins in a concerted fashion, maintaining the stereochemistry of the reactant olefin. Triplet quenchers such as butadiene solvents can be used to increase stereospecific yields.[9] Halogenated solvents also stabilize the singlet state.[2][7] For example, dibromomethane and hexafluorobenzene deactivate the higher-energy singlet state,[9] decelerating the rate of intersystem crossing in accordance with earlier studies of diphenylcarbene.[2] The mechanism of singlet state deactivation is theorized to occur through halogen-lone pair complexation of empty 1Fl P-orbitals.[7] See also
References1. ^1 {{Cite journal| last4 = Kaufmann | first1 = P. B.| last2 = Brauer| last5 = Schuster| last3 = Zupancic | first2 = B. E.| first3 = J. J.| last1 = Grasse| first4 = K. J.| first5 = G. B.| title = Chemical and physical properties of fluorenylidene: equilibration of the singlet and triplet carbenes| journal = Journal of the American Chemical Society| volume = 105| issue = 23| pages = 6833| year = 1983 | doi = 10.1021/ja00361a014}} 2. ^1 2 {{cite journal|author1=Sitzmann, E. V. |author2=Langan, J. |author3= Eisenthal, K. B. |last-author-amp=yes |title=Intermolecular effects on intersystem crossing studied on the picosecond timescale: the solvent polarity effect on the rate of singlet-to-triplet intersystem crossing of diphenylcarbene|journal=Journal of the American Chemical Society|year=1984|volume=106|issue=6|pages=1868–1869|doi=10.1021/ja00318a069}} 3. ^{{cite journal|author1=Trozzolo, A. M. |author2=Murray, R. W. |author3=Wasserman, E. |journal=J. Am. Chem. Soc.|year=1962|issue=84|pages=4990}} 4. ^{{cite journal|author1=Moritani, I. |author2=Murahashi, S.-I. |author3=Yoshinaga, K. |author4=Ashitaka, H. |journal=Bull. Chem. Soc. Jpn.|year=1967|volume=40|pages=1506}} 5. ^1 {{cite book|last=Leffler|first=J. E.|title=An introduction to free radicals (Vol. 58).|year=1993|publisher=Wiley|location=NY etc.}} 6. ^{{cite book|last=Isaacs|first=N. S.|title=Reactive intermediates in organic chemistry|year=1974|publisher=Wiley|location=London}} 7. ^1 2 {{cite journal|author1=Wang, J. |author2=Kubicki, J. |author3=Hilinski, E. F. |author4=Mecklenburg, S. L. |author5=Gustafson, T. L. |author6= Platz, M. S. |last-author-amp=yes|title=Ultrafast study of 9-diazofluorene: Direct observation of the first two singlet states of fluorenylidene|journal=Journal of the American Chemical Society|year=2007|volume=129|issue=44|pages=13683–13690|doi=10.1021/ja074612w |pmid=17935331}} 8. ^{{cite journal|author1=Skell, P. S. |author2= Woodworth, R. C. |last-author-amp=yes |title=Structure of Carbene, CH2|journal=Journal of the American Chemical Society|year=1956|volume=78|issue=17|pages=4496–4497|doi=10.1021/ja01598a087}} 9. ^1 2 3 {{cite book|author1=CJ Moody |author2=GH Whitham |title=Reactive Intermediates|year=1992|publisher=Oxford University Press}} 4 : Carbenes|Reactive intermediates|Functional groups|Fluorenes |
| 随便看 |
|
开放百科全书收录14589846条英语、德语、日语等多语种百科知识，基本涵盖了大多数领域的百科知识，是一部内容自由、开放的电子版国际百科全书。