5 years ago

Twisting of Alkynes towards a Carbon Double Helix

Twisting of Alkynes towards a Carbon Double Helix
Gebhard Haberhauer, Abdulselam Adam
The carbon allotrope exhibiting only one-dimensional sp-hybridized carbon atoms is called carbyne. However, its existence is very controversial. Studies on model compounds for carbyne revealed that many oligoalkynes show not a straight, but a bent structure of the carbon chain. Here, we question whether it would also be possible to obtain a more complex structure from carbyne, such as a dimeric double helix. Based on quantum chemical calculations, we show that only a small energetic expense is needed for the formation of a double helix starting from oligoalkyne chains. In some cases, the double helix-like conformation is more stable than the corresponding conformation with a parallel arrangement of the acetylene chains. Furthermore, model systems were synthesized in which two diphenyl oligoalkyne chains are fixed and twisted by a chiral imidazole-containing clamp. A structural investigation of these model systems was performed based on UV and CD spectroscopy and quantum chemical calculations. The observed twisting in these model systems can be regarded as the first small step towards an imaginable carbon double helix. Search for a carbon double helix: Calculations show that only small energetic effort is required for a three-dimensional twisting of oligoalkynes. This kind of three-dimensional twisting could be experimentally proved by the synthesis of model systems in which two diphenyl oligoalkyne chains are fixed and twisted by a chiral imidazole-containing clamp (see figure).

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201701096

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