Annulyne

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Annulynes or dehydroannulenes are conjugated monocyclic hydrocarbons with alternating single and double bonds in addition to at least one triple bond.

Annulynes
Annulynes

They are related to

EPR spectroscopy. [10]annulyne, like [4]annulyne, only exists in theory.[1]

[8]Annulyne trimerization in presence of base
[8]Annulyne trimerization in presence of base

[12]annulyne has been observed in 2005 by Stevenson et al. in solution by

NMR spectroscopy at room temperature.[2] Reaction of 1,5-hexadiyne and potassium tert-butoxide was reported to yield two isomers 5,9-di-trans-[12]-annulyne and 3,11-di-trans-[12]annulyne in a 1:1 ratio. The proposed reaction sequence involved an unspecified electron transfer reaction. A third single isomer 3,9-di-trans-[12]annulyne could be obtained in three steps from hexabromocyclododecane
.

Unlike other annulynes, the [12]annulyne isomers were found to be very stable and did not self-condense. These annulynes reacted with

radical anions and dianions. The NMR chemical shifts of two internal protons of the dianion were negative and attributed to an aromatic ring current
. The external proton next to the triple bond had a chemical shift of nearly 14, attributed to the positive charge of the potassium cation coordinated to it.

Proposed [12]Annulyne synthesis from 1,5-hexadiyne, Stevenson 2005
Proposed [12]Annulyne synthesis from 1,5-hexadiyne, Stevenson 2005

Two new [12]annulyne isomers were reported in 2008 by the same group.[3]

The Stevenson findings were challenged by Christl and Hopf in 2009.

valence isomerization to biphenyl is very exothermic but also with a high kinetic barrier.[5]

[14]annulyne was reported in 1962 by Jackman et al.[6]

Other annulynes

Dehydroannulenes with more than one triple bond were pioneered by Franz Sondheimer whose research group reported bisdehydro[12]annulene in 1962 [7] and 1,5,9-tridehydro[12]annulene in 1966.[8] A dehydrobenzo[14]annulene was reported in 2001 by Boydston and Haley [9]

Applied research areas

Certain two-dimensional carbon networks containing a repeating dehydroannulene motif have been investigated for potential optoelectronics applications. [10]

References

  1. doi:10.1021/ja0507968
  2. doi:10.1021/ja053886l
  3. doi:10.1002/ange.200803863
  4. doi:10.1002/anie.200901741
  5. doi:10.1021/jo1017537
  6. doi:10.1021/ja00881a022
  7. doi:10.1021/ja00952a034
  8. doi:10.1021/ja00963a057
  9. doi:10.1021/ol016764g
  10. ^ Building Symmetric Two-Dimensional Two-Photon Materials Ajit Bhaskar, Ramakrishna Guda, Michael M. Haley, and Theodore Goodson III J. Am. Chem. Soc., 2006, 128 (43), pp 13972–13973
    doi:10.1021/ja062709x
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