Classify alcohols and select oxidation products from structures.
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Method and worked examples
An alcohol contains a hydroxyl group bonded to a saturated carbon. Classify it by the number of other carbon atoms bonded to that carbon: one for primary, two for secondary and three for tertiary. Methanol is conventionally treated with primary-alcohol oxidation behaviour. Locate each hydroxyl group in the name; multiple groups use endings such as diol or triol.
A primary alcohol can be oxidised to an aldehyde and then a carboxylic acid. Distillation of the aldehyde as it forms limits further oxidation; heating under reflux with excess oxidant favours the acid. Secondary alcohols form ketones. Tertiary alcohols resist normal mild oxidation. Acidified dichromate changes from orange to green when it oxidises a suitable alcohol; its hazardous chemistry is a factual reaction rule here.
Example 1
Classify and oxidise CH3CH(OH)CH2CH3 using acidified dichromate.
The OH-bearing carbon has two carbon neighbours, so butan−2−ol is secondary. It oxidises to CH3COCH2CH3, butan−2−one.
Example 2
Name HOCH2CH2OH and state its hydroxyl count.
The parent has two carbons and OH groups on carbons 1 and 2: ethane−1,2−diol. It has two hydroxyl groups.
Watch out:Tertiary describes three carbon neighbours on the OH-bearing carbon, not the number of OH groups.
Alcohol naming, classification and oxidation practice | Year 12 Chemistry | Ascent Arcade