13.3.1—Organic molecules as either straight-chained,

A carbon skeleton can be straight-chain, branched or cyclic. This describes connectivity; it is separate from whether the molecule is saturated and from the functional group it carries.

Trace the carbon–carbon framework before naming a molecule or counting isomers. A ring closes the chain, while a branch creates a carbon substituent attached to the parent chain.

Butane is straight-chain, 2-methylpropane is branched, and cyclohexane is cyclic. All three are hydrocarbons, but their connectivity and physical properties differ.

A cyclic molecule is not automatically aromatic, and a branched molecule does not have fewer carbon atoms than its unbranched isomer.