The polyacetylene contents of one form of the species Dahlia coccinea Cav. var. coccinea and also of a horticultural form derived from the same species have been examined. The nineteen polyacetylenes detected comprised eight C13, eight C14, and three C17 compounds. Five of them were previously unknown; their isolation, characterisation, and structure determination are described. They are the C14 2,3-disbustituted tetrahydroprans CH3·[C![[triple bond, length as m-dash]](http://hg.y866.cn/compound/lib/scimg/usr/1/J39700000314.jpg)
C]3·CH[graphic omitted]CH·[graphic omitted] and CH3·CH[graphic omitted]CH·[CC]2·CH[graphic omitted]CH·[graphic omitted] (R = H or Ac), and the C17 acetate CH3·CH[graphic omitted]CH·[CC]2·[CH[graphic omitted]CH]2·CH(OAc)·[CH2]3·CH![[double bond, length as m-dash]](http://www.rsc.org/images/entities/char_e001.gif)
CH2.
