Structural Isomers in Organic Chemistry

Overview

This lecture explains structural isomers in organic chemistry, focusing on their definitions, types, and examples relevant for exams.

Structural isomers have the same molecular formula but different structural formulas.
Example: Butane (straight-chain alkane) and 2-methylpropane (branched alkane) are structural isomers with the formula C4H10.
Different functional groups can result in different compounds with the same molecular formula, such as an aldehyde and a ketone with C3H6O.

Three main types: positional isomers, chain isomers, and functional group isomers.

Same molecular formula but differ in the position of a side chain or functional group on the parent chain.
Example: Two compounds with C5H11Cl where chlorine is on different carbons (first vs second carbon).

Same molecular formula but different carbon chain arrangements (straight-chain vs branched).
Example: Hexane (C6H14) as a straight chain vs a branched alkane with a methyl group.

Same molecular formula but different functional groups, thus belonging to different homologous series.
Example: An ester (methyl methanoate) and a carboxylic acid (ethanoic acid) both have C2H4O2.
Ketones and aldehydes are functional group isomers with formula CnH2nO.
Esters and carboxylic acids are functional group isomers with formula CnH2nO2.

Structural Isomer — Compounds with the same molecular formula but different structural formulas.
Positional Isomer — Isomers that differ by the position of a functional group or branch.
Chain Isomer — Isomers with different arrangements of the carbon chain.
Functional Group Isomer — Isomers with the same molecular formula but different functional groups.
Homologous Series — A family of organic compounds with the same functional group and general formula.

Review the general formulas for ketones, aldehydes, esters, and carboxylic acids.
Prepare for more detailed examples of structural isomers in the next video.