Six-membered rings

Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar hexagonal ring with one hydrogen atom attached to each. As it contains only carbon and hydrogen atoms, benzene is a hydrocarbon.

Morpholine is an organic chemical compound having the chemical formula O(CH2CH2)2NH. This heterocycle features both amine and ether functional groups. Because of the amine, morpholine is a base; its conjugate acid is called morpholinium. For example, treating morpholine with hydrochloric acid generates the salt morpholinium chloride. It is a colorless liquid with a weak, ammonia- or fish-like odor. The naming of morpholine is attributed to Ludwig Knorr, who incorrectly believed it to be part of the structure of morphine.

Borazine, also known as borazole, inorganic benzene, is an inorganic compound with the chemical formula B3H6N3. In this cyclic compound, the three BH units and three NH units alternate. The compound is isoelectronic and isostructural with benzene. For this reason borazine is sometimes referred to as “inorganic benzene”. Like benzene, borazine is a colourless liquid with an aromatic odor.

Hexazine (also known as hexaazabenzene) is a hypothetical allotrope of nitrogen composed of 6 nitrogen atoms arranged in a ring-like structure analogous to that of benzene. As a neutrally charged species, hexazine would be the final member of the azabenzene (azine) series, in which all of the methine groups of the benzene molecule have been replaced with nitrogen atoms. The two last members of this series, hexazine and pentazine, have not been observed, although all other members of the azine series have (such as pyridine, pyrimidine, pyridazine, pyrazine, triazines, and tetrazines).

Thiane is a heterocyclic compound and an organosulfur compound with the formula (CH2)5S. It is a saturated six-membered ring with five carbon atoms and one sulfur atom. The compound is a colorless liquid. It can be prepared by the reaction of 1,5-dibromopentane with sodium sulfide:

Phosphorine (IUPAC name: phosphinine) is a heavier element analog of pyridine, containing a phosphorus atom instead of an aza- moiety. It is also called phosphabenzene and belongs to the phosphaalkene class. It is a colorless liquid that is mainly of interest in research.

Arsabenzene (IUPAC name: arsinine) is an organoarsenic heterocyclic compound with the chemical formula C5H5As. It belongs to a group of compounds called heteroarenes that have the general formula C5H5E (E= N, P, As, Sb, Bi).

Hexachlorophosphazene is an inorganic compound with the chemical formula . The molecule has a cyclic, unsaturated backbone consisting of alternating phosphorus and nitrogen atoms, and can be viewed as a trimer of the hypothetical compound (phosphazyl dichloride). Its classification as a phosphazene highlights its relationship to benzene. There is large academic interest in the compound relating to the phosphorus-nitrogen bonding and phosphorus reactivity.

1,3,5-Trithiane is the chemical compound with the formula (CHS). This heterocycle is the cyclic trimer of the otherwise unstable species thioformaldehyde. It consists of a six-membered ring with alternating methylene bridges and thioether groups. It is prepared by treatment of formaldehyde with hydrogen sulfide.

Borabenzene is a hypothetical organoboron compound with the formula C5H5B. Unlike the related but highly stable benzene molecule, borabenzene would be electron-deficient. Related derivatives are the boratabenzene anions, including the parent [C5H5BH]−.

Thiopyran is a heterocyclic compound with the chemical formula C5H6S. It has two isomers, 2H-thiopyran and 4H-thiopyran, which differ by the location of double bonds. Thiopyrans are analogous to pyrans in which the oxygen atoms have been replaced by sulfur atoms.

Boroxine () is a 6-membered heterocyclic compound composed of alternating oxygen and singly-hydrogenated boron atoms. Boroxine derivatives (boronic anhydrides) such as trimethylboroxine and triphenylboroxine also make up a broader class of compounds called boroxines. These compounds are solids that are usually in equilibrium with their respective boronic acids at room temperature. Beside being used in theoretical studies, boroxine is primarily used in the production of optics.

Pyrylium is a cation (positive ion) with formula , consisting of a six-membered ring of five carbon atoms, each with one hydrogen atom, and one positively charged oxygen atom. The bonds in the ring are conjugated as in benzene, giving it an aromatic character. In particular, because of the positive charge, the oxygen atom is trivalent. Pyrilium is a mono-cyclic and heterocyclic compound, one of the oxonium ions.

Germabenzene (C5H6Ge) is the parent representative of a group of chemical compounds containing in their molecular structure a benzene ring with a carbon atom replaced by a germanium atom. Germabenzene itself has been studied theoretically, and synthesized with a bulky 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl or Tbt group. Also, stable naphthalene derivatives do exist in the laboratory such as the 2-germanaphthalene-containing substance represented below. The germanium to carbon bond in this compound is shielded from potential reactants by a Tbt group. This compound is aromatic just as the o

Cyclo[6]carbon is an allotrope of carbon with molecular formula . This theoretical molecule is a ring of six carbon atoms, connected by alternating double bonds. It is, therefore, a member of the [[cyclocarbon|cyclo[n]carbon]] family.

Stannabenzene (C5H6Sn) is the parent representative of a group of organotin compounds that are related to benzene with a carbon atom replaced by a tin atom. Stannabenzene itself has been studied by computational chemistry, but has not been isolated.

1,2-Dihydro-1,2-azaborine is an aromatic chemical compound with properties intermediate between benzene and borazine. Its chemical formula is CBNH. It resembles a benzene ring, except that two adjacent carbons are replaced by nitrogen and boron, respectively. Several other 1,2-azaborines have been synthesized.

Hexasulfur is an inorganic chemical with the chemical formula . This allotrope of sulfur was first prepared by M. R. Engel in 1891 by treating thiosulfate with HCl. Hexasulfur is orange-red and forms a rhombohedral crystal. It is also called cyclo-, ρ-sulfur, ε-sulfur, Engel's sulfur, and Aten's sulfur.

Bismabenzene () is the parent representative of a group of organobismuth compounds that are related to benzene with a carbon atom replaced by a bismuth atom. Bismabenzene itself has been synthesised but not isolated because it is too reactive, tending to instead dimerize in a Diels-Alder addition.

chemical compound

Thiopyrylium is a cation with the chemical formula C5H5S+. It is analogous to the pyrylium cation with the oxygen atom replaced by a sulfur atom.

thumb|right|300px|Structures of some unstable silabenzenes

thumb|Structure of Rh(C8H12)(η6-C5H5BH). Boratabenzene, sometimes called borinate, is the heteroaromatic anion with the formula [C5H5BH]−.

Stibabenzene is an organic chemical compound. Stibabenzene has the chemical formula . The molecule is a derivative of benzene, with one of the carbon atoms in the 6-membered ring replaced by an antimony (Sb) atom. Stibabenzene is a molecule that is considered to be an organoantimony compound due to it containing carbon, hydrogen, and antimony atoms.