Five-membered rings

chemical compound

Phosphole is the organic compound with the chemical formula ; it is the phosphorus analog of pyrrole. The term phosphole also refers to substituted derivatives of the parent heterocycle. These compounds are of theoretical interest but also serve as ligands for transition metals and as precursors to more complex organophosphorus compounds.

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 comp

2,3-Dihydrothiophene is a heterocyclic compound and an organosulfur compound with the formula SC4H6. It is isomeric with the more symmetrical 2,5-dihydrothiophene. Both isomers of dihydrothiophene are colorless liquids with a thioether-like odor. In terms of their reactivity, both isomers exhibit characteristics of alkenes and thioethers, undergoing addition reactions at carbon and oxidation at sulfur. In contrast, thiophene engages in neither reaction.

Boroles represent a class of molecules known as metalloles, which are heterocyclic 5-membered rings. As such, they can be viewed as structural analogs of cyclopentadiene, pyrrole or furan, with boron replacing a carbon, nitrogen and oxygen atom respectively. They are isoelectronic with the cyclopentadienyl cation or abbreviated as and comprise four π electrons. Although Hückel's rule cannot be strictly applied to borole, it is considered to be antiaromatic due to having 4 π electrons. As a result, boroles exhibit unique electronic properties not found in other metalloles.

thumb|right|upright|General chemical structure of fulgides in the uncyclized form. In order to cyclize, at least one of the four R groups must be an aryl group. In organic chemistry, a fulgide is any of a class of photochromic compounds consisting of a bismethylene-succinic anhydride core that has an aromatic group as a substituent. The highly conjugated system is a good chromophore. It can undergo reversible photoisomerization induced by ultraviolet light, converting between the E and Z isomers, both of which are typically colorless compounds. Unlike the more-stable Z isomer, the E isomer can

Cyclopentasilane is a cyclic compound of silicon and hydrogen with the chemical formula . Containing five silicon atoms arranged in a pentagonal ring, it is the silicon analog of cyclopentane. Cyclopentasilane is a colorless pyrophoric liquid. It is an oligosilane. It is of research interest because of its potential use as a liquid silicon ink for printing silicon structures on integrated circuits or solar cells.

Cyclopentyne is a cycloalkyne containing five carbon atoms in the ring. Due to the ideal bond angle of 180° at each atom of the alkyne but the structural requirement that the bonds form a ring, this chemical is a highly strained structure, and the triple bond is highly reactive. The triple bond easily undergoes both [2+2] and [4+2] cycloaddition reactions. Unlike benzyne, which undergoes a [2+2] addition with loss of stereochemistry at the alkene partner, cyclopentyne reacts with alkenes with retention of geometry of the partner, an example of the relevance of orbital symmetry even for highly