Chain isomerism, also known as skeletal isomerism or n-butane isomerism, is a type of structural isomerism in organic chemistry. It occurs when compounds with the same molecular formula have different arrangements of the carbon backbone or chain. In other words, the carbon atoms are connected in a different sequence in each isomer, leading to distinct chemical and physical properties.

Here are a few examples and key points about chain isomerism:

1. Examples: One common example of chain isomerism involves alkanes (saturated hydrocarbons) with the molecular formula C4H10:
   • n-Butane: CH3-CH2-CH2-CH3 (straight chain)
   • Isobutane: CH3-CH(CH3)-CH3 (branched chain)
2. Alkanes: Chain isomerism is often observed in alkanes, where the carbon skeleton can have various arrangements of linear chains and branching.
3. Branching: In isomers with branching, one carbon atom forms more than two single bonds, resulting in a branched structure. This can lead to different physical properties and reactivity compared to linear chain isomers.
4. Straight Chain vs. Branched: Straight chain isomers tend to have higher boiling points compared to branched isomers because of increased surface area for intermolecular interactions (London dispersion forces).
5. Chemical Properties: Chain isomerism can lead to differences in chemical reactivity. For example, branched isomers might react differently in substitution or addition reactions due to the accessibility of different carbon atoms.
6. Nomenclature: When naming chain isomers, the prefix “n-” (for normal) is often used to indicate a straight chain. The prefix “iso-” is used to indicate a branched chain.
7. Effect on Properties: The arrangement of atoms in the carbon chain affects properties such as boiling points, melting points, density, and solubility.
8. Functional Groups: Chain isomerism can also occur in compounds containing functional groups. For example, in alcohols, the position of the hydroxyl group can vary along the carbon chain.

Chain isomerism is an important concept in organic chemistry, as it highlights the significance of molecular structure in determining the properties and behavior of organic compounds. Different arrangements of the carbon skeleton can lead to substantial variations in physical and chemical characteristics.