Alkanes containing a methyl group on the second carbon of the main chain are called ?

Alkanes are hydrocarbons containing only single carbon–carbon bonds and are classified based on their structure. When an alkane has a methyl group attached to the second carbon atom of the main chain, it is called an iso-alkane. This classification is part of the branched-chain alkane series, which differs from normal alkanes (n-alkanes) where all carbon atoms are connected in a continuous straight chain.

The “iso” prefix indicates that the alkane has a specific branching pattern, with the methyl group (–CH₃) attached to the second carbon of the main chain. For example, isobutane (C₄H₁₀) is an iso-alkane where three carbon atoms form the main chain and a methyl group branches off the second carbon.

Iso-alkanes are important in organic chemistry because branching affects their physical properties, such as boiling and melting points. Iso-alkanes generally have lower boiling points than their straight-chain counterparts because branching reduces surface area, decreasing van der Waals forces between molecules. Despite the difference in structure, they share the general formula of alkanes, CₙH₂ₙ₊₂.

Other classifications of branched alkanes include neo-alkanes, which have more extensive branching with multiple methyl groups on the end carbon, and branched alkanes, which include any alkane with at least one branch. However, only when a single methyl group is attached to the second carbon does the compound specifically qualify as an iso-alkane.