Polyynes

polymeric allotrope of carbon

thumb|right|Diacetylene, the simplest polyyne

Oenanthotoxin is a toxin extracted from hemlock water-dropwort (Oenanthe crocata) and other plants of the genus Oenanthe. It is a central nervous system poison, and acts as a noncompetitive antagonist of the neurotransmitter gamma-aminobutyric acid. A case has been made for the presence of this toxin in local Oenanthe species playing a causative role in euthanasia in ancient Sardinia. It was crystallized in 1949 by Clarke and co-workers. It is structurally closely related to the toxins cicutoxin and carotatoxin. Oenanthotoxin is a C17 polyacetylene isomer of cicutoxin.

Cyclooctadeca-1,3,5,7,9,11,13,15,17-nonayne or cyclo[18]carbon is an allotrope of carbon with molecular formula . The molecule is a ring of eighteen carbon atoms, connected by alternating triple and single bonds; thus, it is a polyyne and a cyclocarbon.

chemical compound

chemical compound

thumb|right|Chemical structure of cyanoacetylene, the simplest cyanopolyyne

Ichthyothereol is a toxic polyyne compound found in the leaves and flowers of several plants in South and Central America. These plant sources and their extracts are known for their toxic effects on fish, and have long been used by various native tribes in the lower Amazon basin for fishing. The name of the genus Ichthyothere, the members of which contain noticeable amounts of the natural product in their leaves, literally translates as fish poison. It is so toxic, fish will jump out of the water if Ichthyothere terminalis leaves are used as bait. This chemical is also found in the leaves and