Methylene

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Structural formula
Structural formulas of methylene
Structural formula as singlet carbene (left) and as triplet carbene (a diradical , right)
General
Surname Methylene
other names
  • Methylidene
  • Carbene
Molecular formula CH 2
External identifiers / databases
CAS number 2465-56-7
PubChem 123164
Wikidata Q11172462
properties
Molar mass 14.03 g mol −1
Physical state

gaseous

safety instructions
GHS hazard labeling
no classification available
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Methylene is the simplest organic carbene . It is the basic building block for the methylene group .

structure

Bond angles in the singlet state (left) and in the triplet ground state (right).

Methylene has an angular structure and in the triplet ground state has an H, C, H bond angle of 136 °, according to another source it is 135 °.

Singlet methylene is more energetic than triplet carbene. The H, C, H bond angle is given as 103 ° or 105 °.

Extraction and presentation

Methylene can be prepared by photochemical cleavage of diazomethane with the formation of nitrogen .

If you look closely, this produces singlet methylene. If the photochemical cleavage of diazomethane is carried out in the presence of a sensitizer (e.g. benzophenone ), however, triplet methylene is formed. Furthermore, the compound can be produced by reacting diiodomethane with a Zn / Cu alloy in a Simmons-Smith reaction .

The proof of the existence of methylene was first achieved spectroscopically in 1959 by Gerhard Herzberg , who produced it by flash photolysis of diazomethane. Its existence was predicted by JU Nef in Chicago in 1897.

properties

Methylene has a triplet ground state and is therefore paramagnetic . Like molecular oxygen, it can thus be viewed as a diradical . As a reactive intermediate , methylene is stable under special conditions (e.g. under high dilution in inert gas ), but due to the electron sextet it is short-lived and very reactive ( electron deficiency compound ). Addition reactions in particular are very fast and exothermic . Methylene reacts with itself and, at sufficient concentrations, tends to dimerize to ethene .

Individual evidence

  1. ↑ This substance has either not yet been classified with regard to its hazardousness or a reliable and citable source has not yet been found.
  2. ^ Hoffmann, Roald (2005). Molecular Orbitals of Transition Metal Complexes . Oxford. P. 7. ISBN 0-19-853093-5 .
  3. ^ A b Jerry March: Advanced Organic Chemistry , 3rd Edition, John Wiley & Sons, New York, 1985, p. 172, ISBN 0-471-88841-9 .
  4. ↑ a b Reinhard Brückner : Reaction Mechanisms , Spectrum Akademischer Verlag, 3rd corrected edition, 2007, p. 115, ISBN 978-3-8274-1579-0 .
  5. ↑ Szantay Csaba: elméleti Szerves KÉMIA , 4th, átdolgozott, bővített. Edition, Műegyetemi Kiadó, Budapest 1996, p. 287, ISBN 963-420-501-1 .
  6. ^ A b Joachim Buddrus: Fundamentals of Organic Chemistry , 4th edition, de Gruyter Verlag, Berlin, 2011, pp. 178–179, ISBN 978-3-11-024894-4 .
  7. ↑ Entry on carbenes. In: Römpp Online . Georg Thieme Verlag, accessed on April 17, 2013.
  8. ↑ G. Herzberg, J. Shoosmith, Spectrum and structure of the free methylene radical, Nature, Volume 183, 1959, pp. 1801-1802.
  9. ^ Curt Wentrup: Reactive Intermediates I: Radicals, Carbenes, Nitrenes, Strained Rings . Thieme, Stuttgart, 1979, pages 138-204. ISBN 3-13-560101-3 .
  10. ↑ Lazár, Milan: Free radicals in chemistry and biology . CRC Press, Boca Raton 1989, ISBN 0-8493-5387-4 .

literature