Structural isomerism

Structural isomerism is the existence of compounds with the same molecular formula but different atom-to-atom connectivity. These compounds can have different physical and chemical properties.

Molecular formula: A notation that specifies the number of atoms of each element in a molecule. Structural isomers share this count even when their atoms are connected differently.
Chain isomerism: Structural isomerism in which carbon atoms form different skeletal arrangements. Changing the carbon skeleton produces branched and unbranched compounds with the same formula.
Butane: An alkane with molecular formula C₄H₁₀, occurring as straight-chain and branched structural isomers. Its two constitutional isomers show how branching changes structure without changing formula.
Stereoisomerism: Isomerism in which compounds have the same atom-to-atom connectivity but differ in the three-dimensional arrangement of atoms. Unlike structural isomers, stereoisomers preserve the bonding pattern.
Chemical structure: The arrangement of atoms and bonds that defines a chemical species. Connectivity is the structural feature that distinguishes isomers with identical formulas.
Position isomerism: Structural isomerism in which a functional group or multiple bond occupies a different position on the same carbon skeleton. The group remains the same while its attachment point changes.
Ethanol: An alcohol with molecular formula C₂H₆O and a hydroxyl group attached to a carbon atom. Its formula is shared by dimethyl ether, a functional group isomer.
Geometric isomerism: Stereoisomerism caused by restricted rotation, commonly producing cis and trans arrangements. Its compounds differ in spatial arrangement rather than atom-to-atom connectivity.
Chemical bond: An attractive interaction that holds atoms together in molecules or extended substances. Changing which atoms are bonded creates a different structural isomer.
Functional group isomerism: Structural isomerism in which compounds with the same formula contain different functional groups. Different connectivity can place the same atoms into distinct functional groups.

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