Isomers
Isomers share a formula but have different structures.
About this topic
Isomers are compounds with the same molecular formula but different arrangements of atoms, giving different properties. Structural isomers differ in connectivity: butane and methylbutane (C4H10 versus branched) or ethanol and dimethyl ether (both C2H6O). Stereoisomers have the same connectivity but different spatial arrangements, such as cis and trans alkenes and optical isomers.
The number of possible isomers grows quickly: C4H10 has 2, C5H12 has 3, C6H14 has 5 and C10H22 has 75. Chain isomers differ in branching, position isomers in the location of a group or double bond, and functional group isomers in the type of group. Isomers can behave very differently: ethanol is a liquid that is soluble in water, while dimethyl ether is a gas at room temperature. Optical isomers occur where a carbon has four different groups, forming mirror images (enantiomers) like left and right hands.
Example: one enantiomer of limonene smells of oranges and the other of lemons, and in thalidomide one form relieved morning sickness while the other caused birth defects, which showed why pharmaceuticals must control isomers. Cis-but-2-ene and trans-but-2-ene have different boiling points and shapes.
A misconception is that changing the drawing makes a new isomer; rotating around single bonds yields the same molecule. Check the connectivity carefully when counting isomers.
Key ideas
- Chain and positional isomers
- Different properties
- Butane and isobutane
Quick check
Use cases: where Isomers helps
- Homework: review the key idea behind Isomers before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Isomers without notes.
- Visual learning: play with the interactive lab to see how Isomers changes when you adjust its inputs.
- Teaching a friend: explain Isomers in your own words, then compare your version with the key ideas.
Chemistry explains medicine, food, cleaning products, fuels and building materials.
Frequently asked questions
What is Isomers?
Isomers share a formula but have different structures.
What will I learn in Isomers?
Chain and positional isomers. Different properties. Butane and isobutane.
Is Isomers part of Chemistry?
Yes. It is one of 150 Chemistry topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Isomers lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Isomers?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.