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UPMSP Intermediate Chemistry study materials
UPMSP Intermediate Chemistry study resources

UPMSP Intermediate Chemistry: Basic Principles of Organic Chemistry and Hydrocarbons

UPMSP Intermediate Chemistry · Work through your exam, one topic at a time.

All guide sections

Basic Principles of Organic Chemistry and Hydrocarbons

This domain tests IUPAC naming and isomerism, electronic effects, carbocation stability and aromaticity, plus the characteristic reactions of alkanes, alkenes, alkynes and benzene.

Electronic effects

  • Inductive effect: σ-bond polarisation, weak and distance-dependent; –NO₂, –CN, –COOH and halogens withdraw, alkyl groups donate.
  • Resonance: π delocalisation; more equivalent structures means greater stability (carboxylate ion, benzene).
  • Hyperconjugation: σ(C–H) donation stabilises carbocations and alkenes.
  • Carbocation stability: 3° > 2° > 1° > CH₃⁺, with benzylic and allylic cations especially stable.
  • Hückel rule: cyclic, planar, fully conjugated, 4n + 2 π electrons - benzene (6), cyclopentadienyl anion (6), tropylium (6); cyclooctatetraene (8) is non-aromatic and tub-shaped.

Hydrocarbons

Alkanes undergo free-radical halogenation; chlorine is more reactive but less selective than bromine. Alkenes undergo electrophilic addition, following Markovnikov's rule because the more stable carbocation forms. The peroxide effect reverses the regiochemistry only with HBr. Ozonolysis cleaves the double bond to carbonyl fragments. Terminal alkynes are acidic (sp carbon) and give acetylides with NaNH₂; hydration gives an enol that tautomerises to a ketone.

Benzene

Electrophilic substitution: nitration, sulphonation, halogenation (FeX₃ or AlCl₃), Friedel–Crafts alkylation and acylation. –NO₂, –CN, –SO₃H deactivate and direct meta; –OH, –NH₂, –OR and alkyl activate and direct ortho/para; halogens deactivate yet direct ortho/para.

Worked example

Propene plus HBr gives 2-bromopropane. With benzoyl peroxide it gives 1-bromopropane. The peroxide generates Br•, which adds to the terminal carbon to produce the more stable secondary radical; hydrogen abstraction then leaves bromine on carbon 1, the anti-Markovnikov product.

Traps that cost marks

  • Extending the peroxide effect to HCl or HI (only HBr works).
  • Calling a non-planar or non-conjugated ring aromatic.
  • Forgetting that halogen substituents are deactivating yet ortho/para directing.
  • Ignoring E/Z and cis/trans descriptors in names.