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  Cycloalkanes (also called naphthenes) are chemicals with one or more carbon rings to which hydrogen atoms are attached according to the formula CnH2n. 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.

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See also: IUPAC nomenclature


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


Cycloalkanes are similar to alkanes in their general physical properties, but they have higher boiling points, melting points, and densities than alkanes. This is due to stronger London forces because the ring shape allows for a larger area of contact. Cycloalkanes exhibit almost the same degree of unreactivity as alkanes, due to their containing only unreactive C-C and C-H bonds; however, the ring strain (see below) can cause cycloalkanes to be more reactive.

Ring strain

The carbon atoms in cycloalkanes are sp3 hybridized and therefore a deviation from the ideal tetrahedral bond angles of 109.47 degrees causes an increase in potential energy and an overall destabilizing effect. Eclipsing of hydrogen atoms is an important destabilizing effect, as well. The strain energy of a cycloalkane is the theoretical increase in energy caused by the compound's geometry, and is calculated by comparing the experimental standard enthalpy change of combustion of the cycloalkane with the value calculated using average bond energies.

Ring strain is highest for cyclopropane, in which the carbon atoms form a triangle and therefore have 60 degree C-C-C bond angles. There are also three pairs of eclipsed hydrogens. The ring strain is calculated to be around 120 kJ/mol. Cyclobutane has the carbon atoms in a puckered square with approximately 90-degree bond angles; "puckering" reduces the eclipsing interactions between hydrogen atoms. Its ring strain is slightly less, at around 110 kJ/mol. For a theoretical planar cyclopentane the C-C-C bond angles would be 108 degrees, very close to the measure of the tetrahedral angle. Actual cyclopentane molecules are puckered, but this changes only the bond angles slightly so that angle strain is relatively small. The eclipsing interactions are also reduced, leaving a ring strain of about 25 kJ/mol.







International Union of Pure and Applied Chemistry (1995). "Cycloalkanes". Compendium of Chemical Terminology Internet edition.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Cycloalkane". A list of authors is available in Wikipedia.