Intermediate Topic 743 of 1102 Organic Chemistry
Functional Group Isomerism
Isomers with the same formula but different functional groups, such as ethanol and dimethyl ether.
In-depth explanation of Functional Group Isomerism
Functional group isomers share the same molecular formula but contain different functional groups, so they belong to different families of compounds. Because the functional groups differ, the isomers have very different physical properties and chemical behaviour. For example, alcohols form hydrogen bonds with one another and have relatively high boiling points, while ethers cannot hydrogen bond to each other and boil much lower. Recognizing this type of isomerism is important when identifying an unknown compound from its formula and spectroscopic data.
Going deeper: Functional Group Isomerism
Key ideas: Isomers with the same molecular formula but different functional groups, such as ethanol and dimethyl ether (C2H6O), propanal and propanone (C3H6O), and carboxylic acids and esters (CnH2nO2). Their properties differ greatly: ethanol boils at 78 C while dimethyl ether boils at minus 24 C because of hydrogen bonding.
Common mistakes and connections: A frequent mistake is thinking alkenes and alkynes can be functional isomers; they have different formulas, but alkynes and dienes are isomers (CnH2n-2) and alkenes pair with cycloalkanes. Links to qualitative tests, which distinguish these isomers, and to IR spectroscopy.
Visualization of Functional Group Isomerism
Both are C2H6O, but ethanol (an alcohol) hydrogen bonds and boils at 351 K while dimethyl ether boils at 249 K. The interactive lesson shows this as a live animation or chart.
Worked example and use case
The formula C2H6O corresponds to ethanol, an alcohol, and dimethyl ether, an ether, which have very different boiling points.
Frequently asked questions about Functional Group Isomerism
What is Functional Group Isomerism?
Isomers with the same formula but different functional groups, such as ethanol and dimethyl ether.
Is Functional Group Isomerism a beginner, intermediate or advanced topic?
Functional Group Isomerism is a intermediate topic in Organic Chemistry. It builds on the vocabulary of beginner topics in this area.
What should I learn before Functional Group Isomerism?
Study these earlier topics in Organic Chemistry first: Structural Isomerism, Chain Isomerism, Position Isomerism.
What comes after Functional Group Isomerism?
The next topics in Organic Chemistry are Stereoisomerism and Cis-Trans Isomerism.
Can I practise Functional Group Isomerism with quizzes?
Yes. The interactive lesson includes a self-check question on Functional Group Isomerism, and the Organic Chemistry quiz draws on every topic in this area.
Where Functional Group Isomerism fits in Organic Chemistry
Functional Group Isomerism is topic 15 of 148 in Organic Chemistry.