Organic Chemistry: Oxygen- and Nitrogen-Containing Compounds
Core concepts
Know alcohols, phenols, ethers, aldehydes, ketones, carboxylic acids, esters, and nitrogen compounds such as amines and amides. Focus on functional-group reactions: oxidation of primary alcohols to aldehydes and then acids, secondary alcohols to ketones, esterification, hydrolysis of esters, and the basicity of amines. Understand distinguishing tests: Fehling's or Tollens' for aldehydes, sodium carbonate for carboxylic acids, and the smell of esters.
Traps that appear in questions
- Oxidation products: primary alcohols can go to aldehydes or acids depending on conditions; secondary alcohols give ketones; tertiary alcohols resist oxidation.
- Aldehyde vs ketone: only aldehydes reduce Tollens' and Fehling's reagents.
- Esterification: it is reversible, needs an acid catalyst, and produces water; hydrolysis reverses it.
- Amine basicity: amines are basic because of the lone pair on nitrogen; aromatic amines are weaker bases than aliphatic amines.
- Phenol acidity: phenol is weakly acidic, more so than alcohols, because the phenoxide ion is stabilised by the ring.
Worked example
Which compound gives a silver mirror with Tollens' reagent? An aldehyde such as ethanal is oxidised to the acid while Ag⁺ is reduced to silver metal; a ketone such as propanone does not react.
Rule of thumb
Use the functional group to predict reactions, and use specific tests to confirm the group.