A cycloalkene or cycloolefin is a type of alkene

Alkene

In organic chemistry, an alkene, olefin, or olefine is an unsaturated chemical compound containing at least one carbon-to-carbon double bond...

 hydrocarbon

Hydrocarbon

In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....

 which contains a closed ring of carbon

Carbon

Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

 atom

Atom

The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...

s, but has no aromatic

Aromaticity

In organic chemistry, Aromaticity is a chemical property in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibit a stabilization stronger than would be expected by the stabilization of conjugation alone. The earliest use of the term was in an article by August...

 character. Some cycloalkenes, such as cyclobutene

Cyclobutene

Cyclobutene is a cycloalkene. It is used in the chemical industry as a monomer for synthesis of some polymers and for a range of chemical syntheses.- External links :*...

 and cyclopentene

Cyclopentene

Cyclopentene is a chemical compound with the formula 58. It is a colorless liquid with a petrol-like odor. It is one of the cycloalkenes.Cyclopentene is produced industrially in large amounts...

, can be used as monomer

Monomer

A monomer is an atom or a small molecule that may bind chemically to other monomers to form a polymer; the term "monomeric protein" may also be used to describe one of the proteins making up a multiprotein complex...

s to produce polymer

Polymer

A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...

 chains. Unless the rings are very large, cycloalkenes are always the cis isomers, and the term cis is omitted from the names. In a large ring, a trans double bond may occur, giving a trans-cycloalkene.