Organic Chemistry: Hydrocarbons and Functional Derivatives
Organic Chemistry: Hydrocarbons and Functional Derivatives tests structure and nomenclature, the characteristic reactions of each homologous series, and the simple tests that distinguish functional groups.
Core reactions
- Alkanes: free-radical substitution with halogens under UV light or heat; cracking.
- Alkenes and alkynes: electrophilic addition. Markovnikov's rule - hydrogen adds to the carbon bearing more hydrogens, via the more stable carbocation. HBr with peroxides gives the anti-Markovnikov product.
- Arenes: electrophilic substitution (nitration with HNO₃/H₂SO₄, halogenation with FeBr₃) rather than addition.
- Alcohols oxidise to aldehydes or ketones and then to acids; tertiary alcohols resist oxidation.
- Aldehydes reduce Tollens' reagent to a silver mirror and Fehling's solution to a red precipitate; ketones do not.
- Carboxylic acids with alcohols give esters (H₂SO₄ catalyst); esters hydrolyse back to acid and alcohol.
Worked example
Propene with HBr gives 2-bromopropane. Protonation at C-1 leaves a secondary carbocation at C-2, more stable than the primary carbocation formed by protonation at C-2, so bromide attacks C-2. With HBr and a peroxide, the bromine radical adds to the terminal carbon to give the more stable secondary radical, and hydrogen abstraction then yields 1-bromopropane.
Traps
- The peroxide effect operates with HBr only, not HCl or HI.
- Drawing benzene with three fixed double bonds and predicting addition products from it.
- Forgetting that bromine water is decolourised by alkenes and phenols but not by benzene.