ChemOrga / Functional Groups

Organic Functional Groups

Each organic function is defined by a specific functional group — the set of atoms that gives the molecule its characteristic chemical behavior. Pick a function below to see the definition, general formula, naming rule, properties, applications and worked examples.

How to identify one quickly

Look for the repeating structural pattern. C=C indicates an alkene; C≡C, an alkyne; C=O at the end of a chain, an aldehyde; and C=O between carbons, a ketone. Heteroatoms help too: -OH suggests an alcohol, -COOH a carboxylic acid, -COO- an ester, -O- an ether, -NH₂ an amine, and -CONH₂ an amide.

AlkanesHydrocarbons with only single bonds AlkenesHydrocarbons with one or more double bonds AlkynesHydrocarbons with a triple bond AlcoholHydroxyl group (-OH) on a saturated carbon AldehydeCarbonyl at the end of the chain (-CHO) KetoneCarbonyl in the middle of the chain Carboxylic acid-COOH group EsterDerived from acid + alcohol EtherOxygen linking two carbon chains AmineAmmonia derivative with carbon AmideCarbonyl bonded to nitrogen NitrileCyano group –C≡N Acyl halideReactive acid derivative –COX Sulfonic acidSulfonic group –SO₃H Organic halideHalogen (F, Cl, Br, I) bonded to carbon

Comparison map

A molecular formula can be shared by different compounds. What defines the function is connectivity: which atoms are bonded, and what type of bond connects them.

FunctionCharacteristic groupUseful behavior clueKnown example
Alkanesingle C–Cnonpolar and relatively unreactivepropane
AlkeneC=Caddition and polymerizationethene
AlkyneC≡Clinear geometry and additionethyne
AlcoholR–OHhydrogen bondingethanol
AldehydeR–CHOterminal carbonyl and easy oxidationethanal
KetoneR–CO–R'internal carbonyl and solvent behaviorpropanone
Carboxylic acidR–COOHacidity and hydrogen-bonded dimersethanoic acid
EsterR–COO–R'hydrolysis and characteristic aromasethyl ethanoate
EtherR–O–R'accepts, but does not donate, Hethoxyethane
AmineR–NH₂ / R₂NH / R₃Nbasicity and protonationmethanamine
AmideR–CONH₂resonance and peptide bondsethanamide
HalideR–Xsubstitution and eliminationchloromethane

Why the function matters

The functional group changes polarity, boiling point, solubility, acidity, basicity, and reactivity. That is why ethanol and ethyl ethanoate, even though both contain carbon, hydrogen, and oxygen, differ greatly in odor, miscibility, and reactions.

Study route
  1. Identify the functional group in the structure.
  2. Compare its polarity and intermolecular interactions.
  3. Learn the suffix when it is principal and prefixes when it is not.
  4. Test a structure in the simulator and inspect the name breakdown.

Priority order (IUPAC)

When a molecule has more than one functional group, only one becomes the suffix (the "main group") — the others become prefixes. The priority order, from highest to lowest, is:

  1. Carboxylic acids
  2. Esters
  3. Amides
  4. Nitriles
  5. Aldehydes
  6. Ketones
  7. Alcohols / Phenols
  8. Amines
  9. Ethers

Sulfonic acids and acyl halides are also important acid derivatives. Simple halides are always prefixes, never suffixes. See the full detail in IUPAC nomenclature.

Build a molecule in the simulator →