Structural Isomerism

Chain Isomerism: Same molecular formula, different carbon skeleton arrangements.

Position Isomerism: Same carbon skeleton, different position of functional group/substituent/unsaturation.

Functional Group Isomerism: Same molecular formula, different functional groups (e.g., Alcohols vs. Ethers; Aldehydes vs. Ketones).

Metamerism: Same functional group, different alkyl chain distribution on either side of a polyvalent heteroatom ($$\text{--O--}, \text{--S--}, \text{--NH--}$$).

Ring-Chain Isomerism: Compounds having the same molecular formula existing in open-chain and cyclic forms (e.g., Propene and Cyclopropane).