Types of structure isomerism

Chain or nuclear isomerism

Two organic compounds having same molecular formula differ in the nature of the carbon atom chain. This kind of isomerism is known as chain or nuclear isomerism. For e.g., n-butane and isobutane, have the same molecular formula C₄H₁₀. While n-butane is a straight chain, isobutane has a branched structure.

Position isomerism

When the same substituent occupies different positions in organic compounds having same molecular formula, the compounds exhibit position isomerism. For e.g.,

H₃C-CH₂-CH₂-I is n-propyl iodide or 1-iodopropane and H₃C-CHI-CH₃ is isopropyl iodide or 2-iodopropane.

Note that both the compounds have the same molecular formula C₃H₇I. In n-propyl iodide the substituent is attached to the first carbon atom whereas in isopropyl iodide it is attached to the second carbon atom.

Functional isomerism

Organic compounds having same molecular formula but different functional groups exhibit functional isomerism. For e.g., ethanol (C₂H₅OH) and methoxy methane (H₃C-O-CH₃) have the same molecular formula C₃H₆O. But the functional group in ethanol is the alcohol group whereas in methoxy methane, it is the ether group.

Metamerism

Some members of the same homologous series differ in the nature of the alkyl groups attached to the polyvalent atom of the functional group. Such compounds are said to exhibit metamerism.

For e.g., diethyl ether (H₅C₂OC₂H₅), methyl n-propyl ether (H₃COCH₂CH₂H₃C) and methyl isopropyl ether [H₃COCH(CH₃)₂]are metamers. All of them have the same molecular formula C₄H₁₀O but the alkyl groups are different.

Tautomerism

Tautomerism is a dynamic isomerism where one isomer is constantly changing into the other and vice versa. For e.g., alky cyanides (RCN) and alkyl isocyanides (RNC) are tautomers.