Chapter 8 — Organic Chemistry – Some Basic Principles and Techniques
Carbon builds more compounds than all the other elements together. This chapter gives you the toolkit for all of them: how carbon bonds and how structures are drawn, how compounds are classified and named, why one formula can mean many isomers, how electrons move when bonds break and form, and how a new compound is purified and analysed.
In the Easter holidays of 1856, eighteen-year-old William Perkin tried to make the antimalarial drug quinine in a makeshift laboratory at his home in London, by oxidising a compound obtained from coal tar. He failed — the flask filled with a black sludge. But when he washed it out with alcohol, it gave a brilliant purple solution. Perkin purified the dye, patented it as "mauve", and within a few years the new colour was worn across Europe and the synthetic chemical industry had begun. Quinine itself was not made in the laboratory for almost another century: nobody yet knew how its atoms were arranged.
That gap is what this chapter closes. To make, name or understand an organic compound you need to know how carbon bonds and how to draw a structure; how to sort compounds into families by skeleton and functional group; how to give a structure a name that anyone in the world can turn back into the same structure; why the same molecular formula can stand for several different compounds; how bonds break and electrons are displaced when organic molecules react; and how a compound is separated, purified and analysed to find which elements it contains, and how much of each. These ideas are the foundation of Chapter 9 (Hydrocarbons) and of all the organic chemistry of Class 12, and they appear in every Board, JEE and NEET paper.
- relate the hybridisation of carbon ($sp^{3}$, $sp^{2}$, $sp$) to the shapes of organic molecules, and count σ and π bonds;
- write complete, condensed, bond-line and wedge–dash formulae and convert between them;
- classify compounds as acyclic, alicyclic, aromatic or heterocyclic, recognise the common functional groups and use homologous series;
- name and draw compounds with the IUPAC rules — parent chain, lowest locants, alphabetical order, functional-group suffixes and priority, substituted benzenes;
- identify chain, position and functional isomers and metamers, count the structural isomers of small formulae, and recognise geometrical isomerism and chiral carbons;
- describe homolytic and heterolytic fission, the structure and stability of carbocations, carbanions and free radicals, and classify reagents as electrophiles or nucleophiles;
- use the inductive, electromeric and resonance effects and hyperconjugation to explain acidity and stability, and classify reactions as substitution, addition, elimination or rearrangement;
- choose a purification method, calculate $R_{f}$ values, describe the tests for C, H, N, S, halogens and P, and calculate percentage composition by the Liebig, Dumas, Kjeldahl and Carius methods.
Sections in this chapter
Carbon's Bonding, Structural Formulae and Classification
Tetravalence and hybridisation of carbon, σ and π bonds; complete, condensed, bond-line and wedge–dash formulae; acyclic, alicyclic, aromatic and heterocyclic compounds; functional groups and homologous series.
IUPAC Nomenclature and Isomerism
Parent chain, lowest locants and alphabetical order; functional-group suffixes, priority order and substituted benzenes; chain, position and functional isomers, metamers; geometrical and optical isomers.
Reaction Mechanism Basics: Electron Displacement and Intermediates
Homolytic and heterolytic fission, curved arrows; carbocations, carbanions and free radicals; electrophiles and nucleophiles; inductive, electromeric and resonance effects, hyperconjugation; types of reactions.
Purification, Qualitative and Quantitative Analysis
Sublimation, crystallisation, distillation (simple, fractional, reduced pressure, steam), extraction, chromatography; Lassaigne's test; estimation of C, H, N, halogens, S, P and O.