Ch 10 introduces organic halogen compounds — classification, IUPAC nomenclature, preparation methods, nucleophilic substitution (SN1/SN2), elimination reactions, and reactions of haloarenes.
SN2 (bimolecular): one-step, backside attack, Walden inversion, favoured by 1° substrates and strong nucleophiles. SN1 (unimolecular): two-step via carbocation, racemisation, favoured by 3° substrates and weak nucleophiles. Elimination: β-elimination (E1 and E2) competes with substitution, favoured by strong bases and high temperatures.
C-X bond in aryl halides is shorter and stronger (partial double bond due to resonance) → less reactive towards nucleophilic substitution. Reactions: Dow process (NaOH, 300°C, 200 atm), Wurtz-Fittig, Ullmann. Electrophilic substitution: halogen is ortho-/para-directing but deactivating.
Download: https://ncert.nic.in/textbook/pdf/lech201.pdf | Part II: https://ncert.nic.in/textbook/pdf/lech2ps.zip
In SN1, the leaving group departs first, forming a planar carbocation intermediate. The nucleophile can attack from either side of this plane with equal probability, giving a 50:50 mixture of R and S products (racemic mixture). In practice, slight excess inversion may occur due to ion-pair shielding.
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