Alkanes

Alkanes are compounds that consist entirely of atoms of carbon and hydrogen (a class of substances known as hydrocarbons) joined to one another by single bonds. The shared electron pair in each of these single bonds occupies space directly between the two atoms; the bond generated by this shared pair is known as a sigma (σ) bond. Both carbon-carbon and carbon-hydrogen sigma bonds are single strong, nonpolar covalent bonds that are normally the least reactive bonds in organic molecules. Alkane sequences form the inert framework of most organic compounds. For this reason, alkanes are not formally considered a functional group. When a hydrocarbon chain is connected as a substituent to a more fundamental structural unit, it is termed an alkyl group. The simplest examples of alkanes are methane (CH₄; the principal constituent of natural gas), ethane (C₂H₆), propane (C₃H₈; widely used as a barbecue fuel), and butane (C₄H₁₀; the liquid fuel in pocket lighters). Hydrocarbon chains commonly occur in cyclic forms, or rings; the most common example is cyclohexane (C₆H₁₂).