1H-arsole

Arsole, also called arsenole or arsacyclopentadiene, is an organoarsenic compound with the formula C4H5As. It is classified as a metallole and is isoelectronic to and related to pyrrole except that an arsenic atom is substituted for the nitrogen atom. Whereas the pyrrole molecule is planar, the arsole molecule is not, and the hydrogen atom bonded to arsenic extends out of the molecular plane. Arsole is only moderately aromatic, with about 40% the aromaticity of pyrrole. Arsole itself has not been reported in pure form, but several substituted analogs called arsoles exist. Arsoles and more complex arsole derivatives have similar structure and chemical properties to those of phosphole derivatives. When arsole is fused to a benzene ring, this molecule is called arsindole, or benzarsole.

==Nomenclature== Arsole belongs to the series of heterocyclic pnictogen compounds. The naming of cyclic organoarsenic compounds such as arsole is based on an extension of the Hantzsch–Widman nomenclature system approved by IUPAC, as summarized below: {| class="wikitable" style="text-align:center" !Ring size!!Unsaturated ring!!Saturated ring |- | 3||Arsirene||Arsirane |- | 4||Arsete||Arsetane |- | 5||Arsole||Arsolane |- | 6||Arsinine||Arsinane |- | 7||Arsepine||Arsepane |- | 8||Arsocine||Arsocane |- | 9||Arsonine||Arsonane |- | 10||Arsecine||Arsecane |}