Cycloalkane

From Wikipedia, the free encyclopedia

Cycloalkanes (also called naphthenes) are chemical compounds with one or more carbon rings to which hydrogen atoms are attached according to the formula C_nH_2n. Cycloalkanes with a single ring are named analogously to their normal alkane counterpart of the same carbon count: cyclopropane, cyclobutane, cyclopentane, cyclohexane, etc. The larger cycloalkanes, with greater than 20 carbon atoms are typically called cycloparaffins.

Cycloalkanes are classified into small, normal and bigger cycloalkanes, where cyclopropane and cyclobutane are the small ones, cyclopentane, cyclohexane, cycloheptane are the normal ones, and the rest are the bigger ones.

[edit] Nomenclature

See also: IUPAC nomenclature

The naming of polycyclic alkanes such as bicyclic alkanes and spiro alkanes is more complex, with the base name indicating the number of carbons in the ring system, a prefix indicating the number of rings (eg, "bicyclo"), and a numeric prefix before that indicating the number of carbons in each part of each ring, exclusive of vertices. For instance, a bicyclooctane which consists of a six-member ring and a four member ring, which share two adjacent carbon atoms which form a shared edge, is [4.2.0]-bicyclooctane. That part of the six-member ring, exclusive of the shared edge has 4 carbons. That part of the four-member ring, exclusive of the shared edge, has 2 carbons. The edge itself, exclusive of the two vertices that define it, has 0 carbons.

The group of cycloalkanes are also known as naphthenes, as they are compounds of petroleum or naphtha.

[edit] Reactions

The simple and the bigger cycloalkanes are very stable, like alkanes, and their reactions for example radical chain reactions, are like alkanes.

The small cycloalkanes - particularly cyclopropane - have a lower stability due to Baeyer strain and ring strain. They react similarly to alkenes, though they don't react in electrophilic addition but in nucleophilic aliphatic substitution. These reactions are ring opening reactions or ring cleavage reactions of alkyl cycloalkanes. Cycloalkanes can be formed in a Diels-Alder reaction.