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Creators/Authors contains: "Tykwinski, Rik"

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  1. ; ; ; ; ; ; ; (, Langmuir)
    Full Text Available 
  2. ; ; ; ; ; ; (, Chemistry – A European Journal)
    Abstract Chemical reduction of a [4]cumulene with cesium metal was explored, and the structural changes stemming from electron acquisition are detailed using X‐ray crystallography. It is found that the [4]cumulene undergoes dramatic geometric changes upon stepwise reduction, including bending of the cumulenic core and twisting of the endgroups from orthogonal to planar. The structural deformation is consistent with early theoretical reports that suggest that the twisting should occur upon reduction of both even and odd [n]cumulenes. The current results, on the other hand, are inconsistent with a previous experimental study of a [3]cumulene in which the predicted twisting is not observed upon reduction. DFT calculations reveal that the barrier to deformation is an order of magnitude lower in a [3]cumulene than a [4]cumulene, allowing the barrier to be overcome in the solid‐state. 
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  3. ; ; ; ; ; ; ; ; ; (, Journal of Physical Organic Chemistry)
    Abstract The design and synthesis of persistent tetraaryl[4]cumulenes are reported. Derivatives with phenyl endgroups ([4]Phand[4]Ph/Ar*) are susceptible to reactions during synthesis and/or purification that complicate isolation of the desired product, particularly intermolecular dimerization reactions. Incorporation of (3,5‐di‐tert‐butyl)phenyl endgroups (Ar*) provides increased stability, culminating in the stable and isolable [4]cumulene[4]Ar*. Cumulene[4]Ar*remains, however, susceptible to dimerization under pressing conditions, and[4]Ar*also readily reacts with electrophiles under mild conditions that lead to intramolecular cyclization. Given the structural complexity of the side products in these studies (compounds3,10,14,17,18), X‐ray crystallography plays a vital role in their identification. 
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