Organic Chemistry: Some Basic Principles and TechniquesMind Map

Organic compounds are classified on the basis of carbon skeleton and functional groups. Open-chain compounds may be straight or branched, while closed-chain compounds may be alicyclic, aromatic or heterocyclic. Functional groups such as -OH, -CHO, -COOH, -NH₂ and halogens decide characteristic reactions and naming priority. A homologous series is a family of compounds with the same functional group and general formula, where successive members differ by -CH₂-. IUPAC nomenclature gives a systematic name by selecting the longest parent chain, identifying the principal functional group, numbering correctly, naming substituents and using proper suffixes or prefixes. Common names are also important for simple compounds frequently used in NCERT and NEET.

Organic compounds can be represented in several ways depending on how much structural detail is needed. Lewis structures show all valence electrons and bonds. Condensed structures show atom connectivity compactly, while bond-line structures omit carbon symbols and most hydrogens for fast drawing. Isomerism occurs when compounds have the same molecular formula but differ in structure or spatial arrangement. Structural isomerism includes chain, position, functional, metamerism, ring-chain and tautomerism. Stereoisomerism includes geometrical isomerism due to restricted rotation and optical isomerism due to chirality. NEET questions commonly ask students to count isomers, identify cis-trans forms, recognize chiral carbon and convert between structural representations.

Organic reactions are controlled by movement of electrons. Inductive effect is permanent polarization through sigma bonds due to electronegativity differences. Resonance effect is delocalization of pi electrons or lone pairs through conjugation, producing resonance structures and stabilizing molecules or ions. Hyperconjugation is delocalization of sigma electrons of C-H bonds adjacent to an empty p-orbital or pi system. Electromeric effect is temporary complete transfer of pi electrons during attack by a reagent. Bond cleavage may be homolytic, forming free radicals, or heterolytic, forming ions such as carbocations and carbanions. Reaction mechanisms use curved arrows to show electron movement and include substitution, addition, elimination and rearrangement reactions.

Organic compounds obtained from natural sources or laboratory synthesis often contain impurities, so purification is essential before analysis or use. The purification method depends on differences in physical properties such as solubility, volatility, boiling point, sublimation tendency and adsorption. Filtration separates insoluble solids from liquids. Crystallization purifies solids based on solubility differences in hot and cold solvent. Distillation separates volatile liquids from non-volatile impurities or liquids with different boiling points. Fractional distillation is used when boiling points are close. Steam distillation purifies steam-volatile compounds. Sublimation is used for substances that directly convert from solid to vapour. Chromatography separates components based on differential adsorption or partition.

Qualitative analysis identifies which elements are present in an organic compound, while quantitative analysis estimates how much of each element is present. Carbon and hydrogen are detected by heating the compound with copper oxide, forming CO₂ and H₂O, which are tested using lime water and anhydrous copper sulphate. Nitrogen, sulphur and halogens are detected by Lassaigne's test, where sodium fusion converts covalent organic elements into ionic sodium salts such as NaCN, Na₂S and NaX. These ions are then tested by characteristic reactions and colour observations. Quantitative analysis includes estimation of carbon and hydrogen by combustion, nitrogen by Dumas or Kjeldahl method, halogens by Carius method, and sulphur and phosphorus through precipitated compounds.