Inorganic chemistry,annulynes ordehydroannulenes areconjugated monocyclichydrocarbons with alternatingsingle anddouble bonds in addition to at least onetriple bond.

They are related toannulenes, which only have alternating single and double bonds. The smallest member of this class is[4]annulyne but is never observed because the molecule carries too muchangle strain. The next member is[6]annulyne orbenzyne which is areactive intermediate well known inorganic chemistry.[8]annulyne is known to exist but quickly dimerizes or trimerizes; the compound has been trapped as itsradical anion and observed byEPR spectroscopy.[10]annulyne, like [4]annulyne, only exists in theory.^[1]

[12]annulyne has been observed in 2005 by Stevenson et al. in solution byNMR spectroscopy atroom temperature.^[2] Reaction of 1,5-hexadiyne andpotassium 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 fromhexabromocyclododecane.

Unlike other annulynes, the [12]annulyne isomers were found to be very stable and did not self-condense. These annulynes reacted withpotassium metal to formradical anions and dianions. The NMRchemical shifts of two internal protons of the dianion were negative and attributed to anaromatic 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.

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.^[4] They were unable to conceive a plausible mechanism and argued that based on the available spectroscopic data the products formed were in fact two linear 1,3-hexadien-5-yne isomers and not macrocycles. Computational analysis of this compound suggestsvalence isomerization tobiphenyl is very exothermic but also with a high kinetic barrier.^[5]

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

Dehydroannulenes with more than one triple bond were pioneered byFranz 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]

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

• Annulenes
• Cycloalkynes

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