Formula ≠ structure
C₂H₆O is not enough to identify ethanol uniquely.
Dimethyl ether has the same molecular formula but different connectivity. Structural formulas distinguish constitutional isomers that a molecular formula alone cannot.
Molecular compound · alcohol
Ethanol
C₂H₆O
Ethanol is a two-carbon alcohol with the structural formula CH₃CH₂OH. Its hydroxyl group gives the molecule a polar, hydrogen-bonding region while the two-carbon chain contributes a less polar hydrocarbon region.
Mixture distinction: alcoholic beverages, fuels and antiseptic products are mixtures. “Ethanol” names the pure molecular compound C₂H₆O, not every liquid that contains it.
Essentials
The –OH group is the structural feature that makes ethanol an alcohol.
The molecular formula C₂H₆O does not reveal which atoms are connected. Writing CH₃–CH₂–OH immediately exposes the hydroxyl functional group and the two-carbon skeleton.
Detail
A conventional 2D structure shows the exact connectivity.
The carbon atoms are connected to each other, and the oxygen sits at the end of the chain as –OH. The O–H bond can donate hydrogen bonds, while oxygen's lone pairs can accept them.
Polarity is local
The molecule is not uniformly polar.
The hydroxyl end interacts strongly with polar environments, while the ethyl group behaves more like a small hydrocarbon. Ethanol's properties reflect both regions.
Understand
Ethanol and water can hydrogen-bond to each other.
The hydroxyl group can both donate and accept hydrogen bonds. This is a major reason ethanol mixes with water much more readily than hydrocarbons of comparable size.
Do not overgeneralize
Hydrogen bonding does not make every alcohol infinitely water-soluble.
As the hydrocarbon part of an alcohol grows, its nonpolar contribution becomes increasingly important. Ethanol is small enough that the hydroxyl group strongly influences bulk miscibility.
Reference identifiers
Names and identifiers that pin down the chemical identity.
| Formula | C₂H₆O / CH₃CH₂OH |
|---|---|
| CAS Registry Number | 64-17-5 |
| PubChem CID | 702 |
| Standard InChI | InChI=1S/C2H6O/c1-2-3/h3H,2H2,1H3 |
| Canonical SMILES | CCO |
Advanced
Push past the first model without losing the simple picture.
Why is ethanol not the only C₂H₆O compound?
Molecular formulas count atoms but do not encode connectivity. Dimethyl ether, CH₃–O–CH₃, is a distinct constitutional isomer.
Does pure ethanol contain water?
Chemically pure ethanol is the compound itself. Real commercial grades can contain water; ethanol and water also form non-ideal mixtures, so composition must be stated separately from molecular identity.
Which atom makes ethanol an alcohol?
The defining motif is an –OH group bonded to a saturated carbon atom. The oxygen alone is not enough; connectivity determines the functional class.
Constituent elements