organic chemistry Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clay ...

, an alicyclic compound contains one or more all-carbon rings which may be either saturated or unsaturated, but do not have

aromatic In chemistry, aromaticity is a chemical property of cyclic (ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to sat ...

character. Alicyclic compounds may have one or more

aliphatic In organic chemistry, hydrocarbons ( compounds composed solely of carbon and hydrogen) are divided into two classes: aromatic compounds and aliphatic compounds (; G. ''aleiphar'', fat, oil). Aliphatic compounds can be saturated, like hexane, ...

side chains attached. The simplest alicyclic compounds are the monocyclic

cycloalkane In organic chemistry, the cycloalkanes (also called naphthenes, but distinct from naphthalene) are the monocyclic saturated hydrocarbons. In other words, a cycloalkane consists only of hydrogen and carbon atoms arranged in a structure containin ...

cyclopropane Cyclopropane is the cycloalkane with the molecular formula (CH2)3, consisting of three methylene groups (CH2) linked to each other to form a ring. The small size of the ring creates substantial ring strain in the structure. Cyclopropane itself i ...

cyclobutane Cyclobutane is a cycloalkane and organic compound with the formula (CH2)4. Cyclobutane is a colourless gas and commercially available as a liquefied gas. Derivatives of cyclobutane are called cyclobutanes. Cyclobutane itself is of no commercia ...

cyclopentane Cyclopentane (also called C pentane) is a highly flammable alicyclic hydrocarbon with chemical formula C5H10 and CAS number 287-92-3, consisting of a ring of five carbon atoms each bonded with two hydrogen atoms above and below the plane. It oc ...

cyclohexane Cyclohexane is a cycloalkane with the molecular formula . Cyclohexane is non-polar. Cyclohexane is a colorless, flammable liquid with a distinctive detergent-like odor, reminiscent of cleaning products (in which it is sometimes used). Cyclohex ...

cycloheptane Cycloheptane is a cycloalkane with the molecular formula C7 H14. Cycloheptane is used as a nonpolar solvent for the chemical industry and as an intermediate in the manufacture of chemicals and pharmaceutical drugs. It may be derived by Clemmens ...

, cyclooctane, and so on.

Bicyclic In chemistry, a bicyclic molecule () is a molecule that features two joined rings. Bicyclic structures occur widely, for example in many biologically important molecules like α-thujene and camphor. A bicyclic compound can be carbocyclic (a ...

alkanes include bicycloundecane,

decalin Decalin (decahydronaphthalene, also known as bicyclo .4.0ecane and sometimes decaline), a bicyclic organic compound, is an industrial solvent. A colorless liquid with an aromatic odor, it is used as a solvent for many resins or fuel additives. I ...

, and

housane Housane or bicyclo .1.0entane is a saturated cycloalkane with the formula C5H8. It is a colorless volatile liquid at room temperature. It was named "housane" because of its shape. Structurally, the molecule consists of cyclopropane fused to cyclob ...

. Polycyclic alkanes include cubane, basketane, and

tetrahedrane Tetrahedrane is a hypothetical platonic hydrocarbon with chemical formula and a tetrahedral structure. The molecule would be subject to considerable angle strain and has not been synthesized as of 2021. However, a number of derivatives have be ...

Spiro compound In organic chemistry, spiro compounds are compounds that have at least two molecular rings with only one common atom. The simplest spiro compounds are bicyclic (having just two rings), or have a bicyclic portion as part of the larger ring sy ...

s have two or more rings that are connected through only one carbon atom. The mode of ring-closing in the formation of many alicyclic compounds can be predicted by

Baldwin's rules Baldwin's rules in organic chemistry are a series of guidelines outlining the relative favorabilities of ring closure reactions in alicyclic compounds. They were first proposed by Jack Baldwin in 1976. Baldwin's rules discuss the relative rates ...

Otto Wallach Otto Wallach (; 27 March 1847 – 26 February 1931) was a German chemist and recipient of the 1910 Nobel Prize in Chemistry for his work on alicyclic compounds. Biography Wallach was born in Königsberg, the son of a Prussian civil servant. His ...

, a German chemist, received the 1910

Nobel Prize in Chemistry ) , image = Nobel Prize.png , alt = A golden medallion with an embossed image of a bearded man facing left in profile. To the left of the man is the text "ALFR•" then "NOBEL", and on the right, the text (smaller) "NAT•" then "M ...

for his work on alicyclic compounds.

Cycloalkenes

Monocyclic

cycloalkene A cycloalkene or cycloolefin is a type of alkene hydrocarbon which contains a closed ring of carbon atoms and either one or more double bonds, but has no aromatic character. Some cycloalkenes, such as cyclobutene and cyclopentene, can be used as mo ...

s are

cyclopropene Cyclopropene is an organic compound with the formula . It is the simplest cycloalkene. Because the ring is highly strained, cyclopropene is difficult to prepare and highly reactive. This colorless gas has been the subject for many fundamental s ...

cyclobutene Cyclobutene is a cycloalkene. It is of interest in research but currently has no practical applications. It is a colorless easily condensed gas. A modern synthesis involves the 2-step dehydration of cyclobutanol. The compound was first prepare ...

cyclopentene Cyclopentene is a chemical compound with the formula . It is a colorless liquid with a petrol-like odor. It has few applications, and thus is mainly used as a minor component of gasoline, present in concentrations of less than 1%. It is one of t ...

cyclohexene Cyclohexene is a hydrocarbon with the formula C6H10. This cycloalkene is a colorless liquid with a sharp smell. It is an intermediate in various industrial processes. Cyclohexene is not very stable upon long term storage with exposure to light a ...

, cycloheptene,

cyclooctene Cyclooctene is the cycloalkene with a formula . Its molecule has a ring of 8 carbon atoms, connected by seven single bonds and one double bond. Cyclooctene is notable because it is the smallest cycloalkene that can exist stably as either the ...

, and so on. Bicyclic alkenes include

norbornene Norbornene or norbornylene or norcamphene is a highly strained bridged cyclic hydrocarbon. It is a white solid with a pungent sour odor. The molecule consists of a cyclohexene ring with a methylene bridge between carbons 1 and 4. The molecule ...

and

norbornadiene Norbornadiene is an organic compound and a bicyclic hydrocarbon. Norbornadiene is of interest as a metal-binding ligand, whose complexes are useful for homogeneous catalysis. It has been intensively studied owing to its high reactivity and distin ...

. Two more examples are shown below, on the left methylenecyclohexane and on the right 1-methylcyclohexene: :

An exocyclic group is always shown outside the ring structure, take for instance the exocyclic double bond of the former molecule. Isotoluenes are a prominent class of compounds with exocyclic double bonds. The placement of double bonds in many alicyclic compounds can be predicted with

Bredt's rule Bredt's rule is an empirical observation in organic chemistry that states that a double bond cannot be placed at the bridgehead of a bridged ring system, unless the rings are large enough. The rule is named after Julius Bredt, who first discussed ...

References

{{Organic-chem-stub Organic compounds