Isomerism

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Definition

The existence of two or more compounds that share the same molecular formula but differ in the arrangement of their atoms. Isomers can have different structures or different spatial orientations, which often gives them different properties.

Worked examples

\(\)C\(_2\)H\(_6\)O\(\): ethanol (drinking alcohol, b.p. 78°C) and dimethyl ether (gas, b.p. -24°C)

Same formula, different structures — ethanol has an –OH group; dimethyl ether has C–O–C — so different properties.

Butane and isobutane both have \(\)C\(_4\)H\(_{10}\) but branch differently

Butane is a straight chain; isobutane branches — structural isomers with different boiling points and densities.

Common mistakes

Isomers have the same formula so they must have identical properties → Isomers have the same formula but different arrangements, giving them different properties The whole point of isomerism is that atom arrangement changes physical and chemical behavior.
Any two molecules with the same number of carbons are isomers → Isomers must have exactly the same molecular formula (same count of every element) Propane and butane both have only C and H, but different totals — not isomers.
Drawing the same molecule rotated or flipped on paper makes it a different isomer → Rotating or flipping the same structure is still the same molecule, not an isomer Isomers differ in connectivity or 3D arrangement, not just orientation on the page.

Where you'll use it next

Isomerism is central to organic chemistry, where you'll classify structural and stereoisomers, predict reactivity, and explain why drugs and biomolecules depend on precise atomic arrangements.

Found in 1 StudyPug lesson

Drawing Enantiomers: Mastering Isomerism and Stereochemistry

Organic Chemistry

Unlock the secrets of molecular structures! Learn how to draw enantiomers and understand isomerism, stereochemistry, and chirality. Boost your organic chemistry skills for better drug design and material creation.

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