8.1: Introduction to Hydrocarbons Hydrocarbons are organic compounds that contain only carbon and hydrogen. The four general classes of hydrocarbons are: alkanes, alkenes, alkynes and arenes. Aromatic compounds derive their names from the fact that many of these compounds in the early days of discovery were grouped because they were oils with fragrant odors. 8.2: Linear Alkanes Simple alkanes exist as a homologous series, in which adjacent members differ by a \(CH_2\) unit. 8.3: Isomerism in Alkanes Alkanes with four or more carbon atoms can exist in isomeric forms. 8.4: Condensed Structural and Line-Angle Formulas Condensed chemical formulas show the hydrogen atoms (or other atoms or groups) right next to the carbon atoms to which they are attached. Line-angle formulas imply a carbon atom at the corners and ends of lines. Each carbon atom is understood to be attached to enough hydrogen atoms to give each carbon atom four bonds. 8.5: IUPAC Nomenclature Alkanes have both common names and systematic names, specified by IUPAC. 8.6: Physical Properties of Alkanes Alkanes are nonpolar compounds that are low boiling and insoluble in water. 8.7: Chemical Properties of Alkanes The alkanes and cycloalkanes, with the exception of cyclopropane, are probably the least chemically reactive class of organic compounds. Alkanes contain strong carbon-carbon single bonds and strong carbon-hydrogen bonds. The carbon-hydrogen bonds are only very slightly polar. Alkanes can be burned, alkanes can react with some of the halogens, breaking carbon-hydrogen bonds, and alkanes can crack by breaking the carbon-carbon bonds. 8.8: Halogenated Hydrocarbons The replacement of an hydrogen atom on an alkane by a halogen atom—F, Cl, Br, or I—forms a halogenated compound. 8.9: Cycloalkanes Many organic compounds have cyclic structures.