Alcohol
An alcohol has a hydroxyl group (-OH) bonded to a saturated (sp³) carbon that isn't part of an aromatic ring (that would be a phenol). Alcohols are classified as primary, secondary, or tertiary depending on whether the carbon carrying the hydroxyl is bonded to 1, 2, or 3 other carbons.
General formula
Naming rule
Name = main chain (which must include the hydroxyl carbon) + suffix -ol, with the position's locant (e.g., propan-2-ol). With 2+ hydroxyls, -diol, -triol etc. are used, without eliding the last letter of the numerical prefix (ethanediol, not ethandiol).
How to name it with IUPAC
Use this sequence to move from the structure to the systematic name:
- Choose the chain containing the carbon bonded to hydroxyl.
- Number to give -OH the lowest locant and use -ol.
- CH₃CH(OH)CH₃ = propan-2-ol: three carbons and hydroxyl at C2.
Examples
| Name | Formula |
|---|---|
| Methanol | CH₃OH |
| Ethanol | C₂H₅OH |
| Propan-2-ol (isopropyl) | (CH₃)₂CHOH |
| Ethane-1,2-diol (ethylene glycol) | C₂H₆O₂ |
Visual examples
See how the functional group appears inside the chain. Compare the drawings with the formulas in the table to practice visual recognition.
Chemical reading
The hydroxyl makes an alcohol polar and able to donate and accept hydrogen bonds, raising boiling point and helping small members dissolve in water.
Properties and applications
Ethanol occurs in beverages and fuels, isopropanol in cleaning, and glycerol in cosmetics. Methanol is toxic.
- Primary alcohols oxidize to aldehydes and then acids; secondary alcohols oxidize to ketones. OH on an aromatic ring is phenol.
- Compare polarity, chain size, and hydrogen bonding before predicting physical properties.