tert‐Butyl‐End‐Capped Polyynes: Crystallographic Evidence of Reduced Bond‐Length Alternation

Cumulene or polyyne? The synthesis and X-ray crystallographic analysis of a series of polyynes up to 20 Csp atoms in length and end-capped with tert-butyl groups has been achieved. The structural data show a distinct reduction in the bond-length alternation as a function of the polyyne length, but this trend appears to saturate before a cumulenic-like structure is achieved.