Chapter 18 · Organic Chemistry
18.12Alcohols
9 min · two checks
Predict
Why does ethanol dissolve in water while octane does not?
The idea
- Name simple alcohols.
- Relate the –OH group to hydrogen bonding and oxidation.
Alcohols are named from the parent chain with the ending -ol, and a number if you must say where the OH sits: ethanol, propan-1-ol, propan-2-ol. Methanol is the one-carbon alcohol, toxic because the body oxidizes it to formaldehyde and formic acid. Ethanol is the alcohol of drinks, also toxic at high dose, and a solvent. Propan-2-ol is rubbing alcohol. The –OH makes boiling points high for the molar mass and gives miscibility with water for the small members.
Alcohols can be primary, secondary, or tertiary depending on how many carbons are attached to the carbon that holds the OH. Primary alcohols oxidize to aldehydes and then to carboxylic acids. Secondary alcohols oxidize to ketones. Tertiary alcohols resist ordinary oxidation because there is no hydrogen on that carbon to remove. Dehydration of an alcohol produces an alkene. These are the two reactions worth being able to predict.
Keep these
- Alcohols: R–OH, named with -ol.
- Small alcohols hydrogen-bond and mix with water.
- Primary → aldehyde → acid. Secondary → ketone.