2-4 Straight-Chain and Branched Alkanes ganes,52ahendgaieanaeeasnen2casss:taigt-dhan CH-CH,-CH-CH CH -CN ight-chain alkanes form a homologous series 8amgh2hkanimconstutionalisomerso cieranaheeietmearomSgouhemeogsofesh There are -Cl-0t-0l 0l-c 2-5 Naming the Alkanes are still used widely usedt certain alkanes. are more precise.The first 20 straigh a为s l Sght-Chais 5 5 2-4 Straight-Chain and Branched Alkanes Alkanes can be classified into three general classes: straight-chain alkanes, branched alkanes, and cycloalkanes: Straight-chain alkanes form a homologous series. The general formula of a straight chain alkane is CnH2n+2. Each member of the series differs from the previous one by the addition of a –CH2-, or methylene, group. Molecules related in this manner are called homologs of each other and the series is called a homologous series. Branched alkanes are constitutional isomers of straight-chain alkanes. Branched chain alkanes have the same molecular formula as straight chain alkanes, CnH2n+2, but differ in connectivity. A branched and straight chain alkane are constitutional isomers of each other. There are three isomeric pentanes: The number of isomeric alkanes increases dramatically with the number of carbon atoms: 2-5 Naming the Alkanes Many common or trivial names are still used widely used to name certain alkanes. Systematic IUPAC names are more precise. The first 20 straight chain alkanes are: