Structural Isomerism — All 5 Types — Notes | NoteTube

Chain isomerism: C4H10 has 2 isomers (n-butane, isobutane). C5H12 has 3. C6H14 has 5. C7H16 has 9.
Position isomerism: Same carbon skeleton, different FG position. 1-butanol vs 2-butanol.
Functional group isomerism: C3H6O can be propanal (aldehyde) or acetone (ketone). C2H6O can be ethanol or dimethyl ether.
Metamerism: Same FG, different alkyl groups around it. Only for ethers, amines, ketones, esters. Example: C4H10O — Et-O-Et vs Me-O-Pr.
Tautomerism: Dynamic equilibrium involving proton shift. Keto-enol (most common), ring-chain, nitroso-oxime. Keto form is usually more stable unless stabilized by conjugation/H-bonding (acetylacetone has ~76% enol in pure liquid).