Cycloalkanes

Cycloalkanes are a class of hydrocarbons that form ring structures and contain only carbon and hydrogen with all carbon atoms sp3-hybridized. Their general formula is CnH2n, reflecting the loss of two hydrogens compared with the corresponding acyclic alkanes. The simplest members are cyclopropane (C3H6), cyclobutane (C4H8), cyclopentane (C5H10), and cyclohexane (C6H12). Like other alkanes, cycloalkanes are nonpolar, relatively nonreactive toward many reagents under mild conditions, and tend to be gases or liquids with low boiling points that increase with molecular size.

Structure and conformations vary with ring size. Small rings exhibit significant angle strain because their bond angles deviate from the ideal tetrahedral angle. Cyclopropane and cyclobutane show noticeable strain and unique reactivity as a result. Cyclohexane is distinguished by its chair conformation, which is comparatively free of angle strain; larger rings can adopt multiple conformations that influence reactivity and physical properties. Substituents on cycloalkanes can display cis/trans (or up/down) relationships when attached to adjacent carbons, contributing to stereoisomerism in less flexible rings.

Reactivity and properties: cycloalkanes are typically liquids or gases at room temperature and are generally insoluble in water but soluble in organic solvents. They undergo typical alkane-type reactions such as free-radical halogenation under UV light and complete combustion to carbon dioxide and water. With strong oxidants, ring systems can be cleaved or oxidized to ketones or carboxylic acids; hydrogenation can convert cycloalkenes or derivatives back to saturated cycloalkanes.

Nomenclature and applications: IUPAC naming uses the cyclo prefix and a number indicating ring size, with substituents given lowest possible locants. Cycloalkanes serve as solvents, intermediates in organic synthesis, and feedstocks for the production of specialty chemicals; cyclohexane, for example, is a common solvent and a precursor in adipic acid synthesis.