Cycloalkane
In organic chemistry, the cycloalkanes (also called naphthenes, but distinct from naphthalene) are the monocyclic saturated hydrocarbons.
[2] The cycloalkanes without side chains (also known as monocycloalkanes) are classified as small (cyclopropane and cyclobutane), common (cyclopentane, cyclohexane, and cycloheptane), medium (cyclooctane through cyclotridecane), and large (all the rest).
Besides this standard definition by the International Union of Pure and Applied Chemistry (IUPAC), in some authors' usage the term cycloalkane includes also those saturated hydrocarbons that are polycyclic.
For example, the name of cyclopropane (C3H6) containing a three-membered ring is derived from propane (C3H8) - an alkane having three carbon atoms in the main chain.
There is more than one convention (method or nomenclature) for the naming of compounds, which can be confusing for those who are just learning, and inconvenient for those who are well-rehearsed in the older ways.
It then has room for an additional numerical prefix if there is the need to include details of other attachments to the molecule such as chlorine or a methyl group.
The base name of the compound, indicating the total number of carbons in both rings (including the shared edge), is listed first.
Cycloalkanes with high angle strain, such as cyclopropane, have weaker C–C bonds, promoting ring-opening reactions.
While variations in enthalpy and orientational entropy of the solid-phase crystal structure largely explain the odd-even alternation found in alkane melting points,[5][6] conformational entropy of the solid and liquid phases has a large impact on cycloalkane melting points.
[7]: 98 [8] For example, cycloundecane has a large number of accessible conformers near room temperature, giving it a low melting point,[9]: 22 whereas cyclododecane adopts a single lowest-energy conformation[9]: 25 (up to chirality) in both the liquid phase and solid phase (above 199 K),[8]: 32–34 and has a high melting point.
These trends are broken from cyclopentadecane onwards, due to increasing variation in solid-phase conformational mobility, though higher cycloalkanes continue to display large odd-even fluctuations in their plastic crystal transition temperatures.
In the most stable chair form of cyclohexane, axial hydrogens on adjacent carbon atoms are pointed in opposite directions, virtually eliminating eclipsing strain.
[23] In the presence of a catalyst and at temperatures of about 495 to 525 °C, naphthenes undergo dehydrogenation to give aromatic derivatives: The process provides a way to produce high octane gasoline.
In another major industrial process, cyclohexanol is produced by the oxidation of cyclohexane in air, typically using cobalt catalysts:[24] This process coforms cyclohexanone, and this mixture ("KA oil" for ketone-alcohol oil) is the main feedstock for the production of adipic acid, used to make nylon.
