BP301T — Pharmaceutical Organic Chemistry II

✔ Correct — C: Hückel's rule (1931) — aromatic if cyclic, planar, every ring atom is sp² (continuous overlap of p-orbitals), and number of π electrons = 4n+2. Antiaromatic if 4n. Examples: benzene 6 π e⁻ (n=1); naphthalene 10 π e⁻ (n=2); cyclopentadienyl anion 6; tropylium cation 6; pyrrole 6 (N lone pair contributes 2); pyridine 6 (N lone pair NOT in ring).

✔ Correct — B: Benzene's resonance energy ≈ 36 kcal/mol — calculated from heat of hydrogenation difference between benzene and three independent C=C (3 × 28.6 = 85.8 kcal/mol expected, but only 49.8 kcal/mol observed → ~ 36 kcal/mol stabilisation). All C-C bond lengths equal (1.39 Å, between single 1.54 and double 1.34). Naphthalene resonance energy ~ 61 kcal/mol; anthracene ~ 84 kcal/mol.

✔ Correct — A: RCOCl + AlCl₃ → RC≡O⁺ AlCl₄⁻ (resonance-stabilised acylium ion). Attacks ring → aryl ketone + HCl. Advantages over F-C alkylation: no rearrangement (acylium is resonance-stabilised); mono-acylation only (ketone product is deactivated → no polyacylation). Limitation: doesn't work on rings deactivated by strong EWGs (-NO₂, -CN, -SO₃H) or with -NH₂/-NHR/-NR₂ (which complex with AlCl₃).

✔ Correct — D: Activating o,p-directors: -NH₂ (strongest), -OH, -OR, -NHR, -NR₂, -NHCOR (mild), -alkyl/-aryl (weak), -F/-Cl/-Br/-I (weak deactivators but o,p-directors due to resonance). Strong deactivating m-directors (-I and -M): -NO₂, -CN, -CHO, -COR, -COOH, -COOR, -CONH₂, -SO₃H, -CF₃, -NR₃⁺. Order of activation/deactivation correlates with σ-Hammett values.

✔ Correct — A: ArH + H₂SO₄/SO₃ ⇌ ArSO₃H + H₂O. Reverse is achieved by heating with dilute H₂SO₄/steam → ArH + SO₃. Used as blocking group: introduce -SO₃H to block para, do EAS at ortho, then remove -SO₃H. Other EAS reactions (halogenation, nitration, F-C) are essentially irreversible because their σ-complex collapse is thermodynamically downhill.

✔ Correct — C: Naphthalene has α (1-, 4-, 5-, 8-) and β (2-, 3-, 6-, 7-) positions. Substitution at α gives Wheland intermediate with more low-energy resonance structures (where one ring stays aromatic) → kinetically preferred. β is thermodynamic (avoids steric peri-interaction). Sulfonation: 80 °C → α; 160 °C → β. Nitration always α. Friedel-Crafts: α.

✔ Correct — B: Anthracene 9,10-positions (centre ring) are most reactive — addition (e.g., Br₂, maleic anhydride in Diels-Alder) at 9,10 gives a product retaining two intact aromatic rings, losing only ~ 36 kcal/mol of resonance energy (vs ~ 84 kcal/mol if all three rings disturbed). This makes anthracene more reactive than benzene/naphthalene as a diene.

✔ Correct — A: Phenanthrene has K-region (9,10-bond, most alkene-like, undergoes addition with Br₂, OsO₄, hydrogenation) and bay region (4,5 — important for carcinogen activation in PAH metabolism: bay-region diol epoxides bind DNA). Phenanthrene resonance energy ~ 92 kcal/mol (slightly more stable than anthracene 84 kcal/mol).

✔ Correct — C: HNO₃ + H₂SO₄ → NO₂⁺ + HSO₄⁻ + H₂O. NO₂⁺ is the nitronium electrophile. Industrial nitration of benzene (50-55 °C) → nitrobenzene. NaNO₂/HCl generates HNO₂ (used for diazotisation of primary aromatic amines, NOT for ring nitration).

✔ Correct — D: Benzene + Cl₂ + FeCl₃ → C₆H₅Cl + HCl. FeCl₃ polarises Cl-Cl: FeCl₃ + Cl₂ → FeCl₄⁻ + Cl⁺. Cl⁺ is the electrophile. Without Lewis acid, Cl₂ alone won't substitute on benzene (C-X bond strength + aromaticity barrier). Fluorination too violent (use Cl₂/Cu-Co); iodination needs an oxidant (HNO₃, H₂O₂) to remove HI.

✔ Correct — A: Wheland (σ) intermediate = arenium ion: electrophile bonded to one ring carbon (now sp³), positive charge delocalised over remaining 5 carbons (ortho + para resonance forms). Loss of H⁺ restores aromaticity → product. Activators stabilise arenium → faster EAS; deactivators destabilise → slower.

✔ Correct — B: F-C alkylation issues: (1) carbocation rearrangement (e.g., 1-chloropropane + benzene + AlCl₃ → mainly cumene, NOT propylbenzene); (2) polyalkylation (alkyl product is more activated than benzene); (3) fails with deactivated rings (-NO₂, -CN, -CHO, -SO₃H); (4) -NH₂ complexes with AlCl₃ — protect as amide first; (5) vinyl/aryl halides don't form stable cations. Acylation avoids these issues.

✔ Correct — C: Birch reduction (SET mechanism): benzene → 1,4-cyclohexadiene; with EDG (e.g., -OMe, -NR₂, -alkyl), reduction occurs at meta/para positions to keep EDG on sp²-C → 2,5-dihydroanisole. With EWG (-COOH, -CONH₂), reduction at the substituted/para positions (sp³ carbons bear EWG). Useful in synthesis to break aromaticity selectively.

✔ Correct — D: Halogens are unique: -I (inductive electron withdrawal — destabilises arenium → slower EAS rate, deactivators) but their lone pairs donate by resonance to ortho/para positions → these positions are slightly more electron-rich than meta → o,p-directing despite deactivation. F best at lone pair donation; F > Cl > Br > I in resonance, but the inductive effect is also strongest with F.

✔ Correct — A: Reimer-Tiemann: phenol + CHCl₃ + NaOH (60 °C) → salicylaldehyde (mainly o-, minor p-). Mechanism: NaOH deprotonates CHCl₃ → CCl₃⁻ → CCl₂ (dichlorocarbene); dichlorocarbene attacks ortho carbon of phenoxide; hydrolysis → -CHO. Yield ~ 30 %. Compare with: Kolbe-Schmitt (phenol + CO₂/NaOH → salicylic acid).

✔ Correct — B: Kolbe-Schmitt: PhO⁻Na⁺ + CO₂ (4 atm, 125 °C) → sodium salicylate; H⁺ → salicylic acid. Mechanism: phenoxide attacks CO₂ at ortho. Used to make aspirin (acetylsalicylic acid by acetylation of -OH with acetic anhydride). With KOH (instead of NaOH), the para isomer is favoured at higher T.

✔ Correct — C: Gattermann-Koch (1897): ArH + CO + HCl + AlCl₃/CuCl → ArCHO. Equivalent of formylation; mechanism involves formyl chloride (HCOCl) generated in situ as electrophile. Useful for direct introduction of -CHO. Variants: Gattermann (HCN/HCl/ZnCl₂); Vilsmeier-Haack (DMF/POCl₃); Duff (hexamine + acid). Étard (CrO₂Cl₂) oxidises -CH₃ → -CHO on aromatic side chain.

✔ Correct — A: Aspirin = acetylsalicylic acid. Synthesis: salicylic acid + (CH₃CO)₂O → C₆H₄(OCOCH₃)(COOH) + CH₃COOH (acid catalysed, e.g., conc H₃PO₄/H₂SO₄). Acetylates the phenolic -OH. Mechanism (NSAID): irreversible acetylation of Ser-530 in COX-1 (Ser-516 in COX-2) → ↓ prostaglandin synthesis. Methyl ester (methyl salicylate, oil of wintergreen) — topical analgesic.

✔ Correct — B: NBS / hν (or peroxide) provides low Br• concentration → preferential abstraction of benzylic H (resonance-stabilised radical) → benzyl bromide. Mnemonic: hν / NBS / peroxide → SIDE CHAIN; Lewis acid (FeBr₃, AlBr₃) → RING. Br₂ alone with no catalyst on toluene doesn't react well; with FeBr₃ → o/p-bromotoluene.

✔ Correct — C: Strong activators (-NH₂, -OH, -OR, -NHR) >> weak (alkyl) > benzene > halogens (weak deactivators) > strong deactivators (-NO₂, -CN, -CHO, -COR, -COOH, -SO₃H, -CF₃, -NR₃⁺). Hammett σ values quantify. Aniline is too reactive to control with HNO₃/H₂SO₄ (oxidised) — protect as acetanilide first.

✔ Correct — A: Phenol pKa ≈ 10 (vs ethanol ~ 16). The phenoxide ion (PhO⁻) is stabilised by resonance — negative charge delocalised onto ring (ortho, para). EWGs further enhance acidity (p-nitrophenol pKa ~ 7.2; picric acid 2,4,6-trinitrophenol pKa ~ 0.4 — strongest organic acid by pKa).

✔ Correct — C: pKa: picric acid 0.4 ≪ p-nitrophenol 7.2 ≪ phenol 10 ≪ p-cresol 10.3 ≪ ethanol 16. Three -NO₂ at o,p positions stabilise phenoxide enormously by resonance + induction → very strong acid (acid strength comparable to carboxylic acids). Picric acid is also explosive, used in dyes/medicine.

✔ Correct — B: Williamson: R-X + R'-O⁻ → R-O-R' + X⁻ (SN2). Primary alkyl halides best (3° → elimination). For unsymmetrical ethers, choose primary R-X. To make t-butyl methyl ether (MTBE): use t-BuO⁻Na⁺ + CH₃Br (NOT MeO⁻ + t-BuBr → elimination). Acid-catalysed dehydration of two alcohols (ROH + ROH → R-O-R + H₂O at 140 °C) gives only symmetrical ethers and only with 1° alcohols.

✔ Correct — D: Ether cleavage: R-O-R' + HI (or HBr, conc) → R-I + R'-OH (initially); then with excess HI → 2 R-X. Mechanism: protonation of O → SN2 by I⁻ (typically attacks less hindered C). Aryl alkyl ether (e.g., anisole): Ar-O-R + HI → ArOH + R-I (NOT Ar-I, because Ar-O bond is hard to cleave; aryl carbocation unstable). Used in Zeisel's method for OMe determination.

✔ Correct — A: Epoxide opening: Acidic — protonated epoxide; nucleophile attacks more substituted C (more stable partial carbocation; Markovnikov). Basic/neutral — Nu⁻ attacks less hindered (less substituted) C (SN2-like). Stereochemistry: anti (backside attack). Examples: arene oxides → trans-diols; epoxide hydrolase in biology. mCPBA epoxidises alkenes.

✔ Correct — C: Phenol is so activated by -OH (+M, strong) that with Br₂/H₂O, it reacts at all three available o,p positions → 2,4,6-tribromophenol (white precipitate; rapid, no Lewis acid catalyst needed). Mono-bromination requires non-aqueous solvent (CCl₄, CS₂) at low T. Aniline behaves similarly with Br₂ → 2,4,6-tribromoaniline.

✔ Correct — A: Industrial: CH₂=CH₂ + ½ O₂ →(Ag, 250 °C) CH₂—CH₂—O (oxirane/ethylene oxide). Lab: 2-chloroethanol + KOH (β-elimination of HCl forms ring). General epoxidation: alkene + mCPBA → epoxide. Ethylene oxide is used as fumigant, sterilant (cold sterilisation of medical devices), in glycol manufacture (→ ethylene glycol), and ethoxylation reactions.

✔ Correct — B: Liebermann's test: phenol + NaNO₂ + conc H₂SO₄ → red colour; on dilution + alkali → blue. Mechanism: phenol nitrosation → 4-nitrosophenol → reacts with another phenol → indophenol dye. FeCl₃ test (option D) is also a phenol test — gives blue/violet/green colour with phenols (forms Fe-phenoxide complex).

✔ Correct — D: Ph-O-Ph = phenoxybenzene (or diphenyl ether — common name). IUPAC: take longer chain as parent; smaller alkoxy as substituent. Common ether names: anisole = methoxybenzene (PhOMe); phenetole = ethoxybenzene; THF = oxolane; dioxane = 1,4-dioxane; THP = oxane. Diphenyl ether is also a heat-transfer fluid (e.g., Dowtherm A).

✔ Correct — A: Claisen rearrangement (1912) — [3,3]-sigmatropic rearrangement of allyl vinyl ether (or allyl aryl ether) to γ,δ-unsaturated carbonyl. Concerted, suprafacial-suprafacial, six-membered chair-like transition state. Aromatic Claisen: allyl phenyl ether (Δ ~ 200 °C) → o-allylphenol. Cope rearrangement is the all-carbon analogue (1,5-hexadiene → another). Both are pericyclic, thermally allowed.

✔ Correct — B: Solubility test for organic acids: NaOH dissolves both phenols and carboxylic acids; NaHCO₃ dissolves only carboxylic acids (effervescence with CO₂). Hence, dissolves in NaOH + NOT in NaHCO₃ = phenol. Used for separating mixtures: extract first with NaHCO₃ (RCOOH out), then NaOH (phenol out). Picric acid and other strong nitro-phenols dissolve in NaHCO₃ (strong acidity).

✔ Correct — A: Diphenols nomenclature: 1,2 = catechol; 1,3 = resorcinol; 1,4 = hydroquinone (quinol); 1,3,5 = phloroglucinol. Catechol oxidises to o-benzoquinone; hydroquinone to p-benzoquinone (used in photography). Resorcinol used in dermatology (acne, dandruff treatment), Seliwanoff's test. Phloroglucinol is antispasmodic (acts on smooth muscle).

✔ Correct — C: Quinones = oxidation products of phenols. p-Benzoquinone (yellow solid) from hydroquinone (oxidation by Na₂Cr₂O₇/H₂SO₄ or autoxidation); o-quinone from catechol. Quinone-hydroquinone redox couple (E° = 0.7 V) — coenzyme Q10 (ubiquinone in ETC), vitamin K (menaquinone), vitamin E (tocopherol involves chromanol). Anthraquinone — vat dyes, anthracycline anticancer drugs (doxorubicin).

✔ Correct — D: Crown ethers (Pedersen, 1967, Nobel 1987) — cyclic polyethers. Naming: x-crown-y where x = total ring atoms, y = oxygen atoms. 18-crown-6 (K⁺ selective; ionic radius match); 15-crown-5 (Na⁺); 12-crown-4 (Li⁺). Encapsulate cation in inner cavity → naked anion in apolar solvent → enhanced reactivity. Used as phase-transfer catalysts (PTC). Cryptands (Lehn) and spherands (Cram) extend this concept to 3D recognition.

✔ Correct — A: Ethers are unreactive at neutral pH (good solvents for many reactions). Cleaved only by strong acids (HI, HBr, conc HCl with ZnCl₂, BBr₃). Mechanism: protonation of O → -OR is now leaving group; primary R undergoes SN2 (I⁻ attacks); tertiary R undergoes SN1 (forms 3° cation). Aryl alkyl ether (anisole + HI): aryl C-O bond unbreakable → ArOH + R-I.

✔ Correct — B: THF (oxolane) — 5-membered saturated cyclic ether. Bp 66 °C. Coordinates lithium and magnesium → solvent for organometallic reactions. Forms peroxides on standing (test before distillation; use BHT inhibitor). Furan is its aromatic counterpart (5-membered, 6 π e⁻). Pyran is the 6-membered O analog; tetrahydropyran = oxane. 1,4-Dioxane is a 6-membered di-oxa ring (used as solvent, suspect carcinogen).

✔ Correct — C: Acid-catalysed dehydration of alcohols: at lower T (~140 °C) → ether (intermolecular); at higher T (~170 °C) → alkene (intramolecular elimination). C₂H₅OH + C₂H₅OH (cat. H₂SO₄, 140 °C) → C₂H₅OC₂H₅ + H₂O. Mechanism: protonation of one alcohol → SN2 attack by second alcohol → ether. Only works for symmetrical ethers from primary alcohols. For unsymmetrical, use Williamson.

✔ Correct — A: Anti-aromatic: cyclic, planar, fully conjugated, 4n π electrons. Cyclobutadiene has 4 π e⁻ — antiaromatic; in practice distorts to rectangular shape (alternating single/double bonds) to relieve antiaromatic destabilisation. Cyclooctatetraene (COT) has 8 π e⁻ but adopts non-planar tub conformation → non-aromatic. COT dianion (10 π e⁻) is planar aromatic.

✔ Correct — B: Lucas reagent = anhydrous ZnCl₂ + conc HCl. Reacts with alcohols → R-Cl (cloudiness). Rate: 3° (immediate, SN1 — stable cation) > 2° (5-10 min) > 1° (no reaction at RT, requires heating). Iodoform test (I₂/NaOH) distinguishes methyl ketones / CH₃CH(OH)R alcohols. Bordwell-Wellman test: chromic acid (CrO₃/H₂SO₄) distinguishes 1°/2° (oxidised) from 3° (no rxn).

✔ Correct — C: Bakelite (Baekeland, 1907) — first fully synthetic plastic. Phenol + HCHO (acid or base catalysed) → highly cross-linked thermoset. Used in electrical insulators, knobs, telephones (historical). Other phenol uses: antiseptic (phenol coefficient reference), salicylic acid → aspirin, picric acid → explosives. Cresol (methyl phenols) is used in disinfectants (Lysol).

✔ Correct — A: C=O is polarised: O δ⁻, C δ⁺. Nucleophiles attack the carbonyl carbon → tetrahedral intermediate (alkoxide) → workup. Aldehydes more reactive than ketones (less steric hindrance + less electron donation by alkyl groups stabilising C=O). Substitutent effects: EWG → ↑ reactivity (e.g., CHO > methyl ketone > ester > amide).

✔ Correct — B: Aldol: 2 CH₃CHO → CH₃CH(OH)CH₂CHO (β-hydroxybutanal); on heating loses H₂O → CH₃CH=CHCHO (crotonaldehyde, α,β-unsaturated). Base (NaOH/EtO⁻) deprotonates α-C → enolate → attacks 2nd carbonyl → addition product (aldol). Acid catalysis goes via enol. Mixed (crossed) aldol useful when one carbonyl has no α-H (PhCHO + acetone → benzalacetone).

✔ Correct — C: Cannizzaro: 2 ArCHO + NaOH → ArCH₂OH + ArCOO⁻Na⁺. One molecule reduced (alcohol), one oxidised (carboxylate). Hydride transfer mechanism. Only with aldehydes lacking α-H (formaldehyde, benzaldehyde, 2,2-dimethylpropanal/pivaldehyde, furfural). Crossed Cannizzaro: HCHO + ArCHO + NaOH → ArCH₂OH + HCOO⁻ (HCHO is preferentially oxidised — better hydride donor).

✔ Correct — D: Tollens' = silver mirror test. Aldehydes (R-CHO) reduce Ag⁺ → Ag⁰ (mirror); RCHO → RCOOH. Doesn't react with ketones (or rarely α-hydroxyketones). Other tests: Fehling's (Cu²⁺ tartrate complex; alkaline) → red Cu₂O ppt; Benedict's (Cu²⁺ citrate); 2,4-DNP (Brady's reagent — yellow/orange precipitate with all aldehydes & ketones); Schiff's reagent (decolourised by aldehydes).

✔ Correct — A: I₂/NaOH (or NaOI) reagent. Iodoform test (+) for: methyl ketones (CH₃CO-R), acetaldehyde (only aldehyde — CH₃CHO), ethanol and CH₃CH(OH)-R alcohols (oxidised first to methyl ketone). Mechanism: α-iodination × 3 → trisubstituted CI₃ → cleavage by OH⁻ → CHI₃ (yellow) + carboxylate. Used to distinguish acetaldehyde from other aldehydes; ethanol from methanol.

✔ Correct — B: NaBH₄ is mild — reduces aldehydes (→ 1° alcohol) and ketones (→ 2° alcohol) only. Compatible with most other functional groups (alkenes, esters, amides, nitriles, NO₂, ArX). LiAlH₄ — much stronger; reduces -COOR, -CONR₂, -COOH, -CN, -NO₂, epoxides. DIBAL-H — partial reduction (ester → aldehyde at low T). Catalytic H₂/Pt or Pd — reduces alkenes, alkynes, nitro, but typically not C=O (slow).

✔ Correct — C: Clemmensen reduction (Zn/Hg + conc HCl, Δ): R₂C=O → R₂CH₂. Used in F-C acylation followed by Clemmensen to introduce straight-chain alkyl groups (avoids rearrangement of F-C alkylation). Wolff-Kishner reduction (NH₂NH₂ + KOH/Δ): same C=O → CH₂ but base conditions, for acid-sensitive substrates. Mozingo reduction (thioacetal + Raney Ni). All three avoid F-C alkylation issues.

✔ Correct — D: Wolff-Kishner: R₂C=O + NH₂NH₂ → R₂C=N-NH₂ (hydrazone); + KOH/heat → R₂CH₂ + N₂ + H₂O. For substrates that are base-stable but acid-sensitive (e.g., have acid-labile groups). Alternative is Clemmensen (Zn/Hg + HCl) for acid-stable substrates. Modified Huang-Minlon procedure (high-bp solvent like ethylene glycol/triethylene glycol) is more practical.

✔ Correct — A: Brady's reagent: 2,4-(NO₂)₂C₆H₃-NH-NH₂ + R₂C=O → R₂C=N-NH-Ar(NO₂)₂ + H₂O. Yellow → orange → red precipitate, sharp m.p. = "fingerprint" for identification. Other carbonyl derivatives: hydroxylamine + R₂C=O → oxime (R₂C=NOH); semicarbazide + R₂C=O → semicarbazone; primary amine + R₂C=O → imine (Schiff base); secondary amine + R₂C=O → enamine.

✔ Correct — B: Acetal = R-CH(OR')₂ (from aldehyde) or ketal R₂C(OR')₂ (from ketone). Mechanism: H⁺ protonates O → -OH leaves → oxocarbenium → R'OH attacks → hemiacetal → repeat → acetal. Acetals are STABLE to base, nucleophiles, reducing agents; hydrolysed by aq acid. Used as PROTECTING GROUPS for carbonyls (cyclic acetal with ethylene glycol, 1,3-dioxolane, easily removed by H₃O⁺). In carbohydrate chemistry, glycosidic bonds are intramolecular acetals.

✔ Correct — C: Grignard summary: HCHO + RMgX → 1° alcohol; RCHO + R'MgX → 2° alcohol; R₂C=O + R'MgX → 3° alcohol; CO₂ + RMgX → carboxylic acid; ester (RCOOR') + 2 R''MgX → 3° alcohol; nitrile (RCN) + R'MgX → ketone (after H₃O⁺); epoxide → β-substituted alcohol. Grignards must be anhydrous (R-H from H₂O/ROH); incompatible with active H or carbonyls present elsewhere.

✔ Correct — A: Perkin synthesis of cinnamic acid (Perkin, 1868): PhCHO + (CH₃CO)₂O + CH₃COO⁻Na⁺ → PhCH=CH-COOH. Mechanism: acetate base deprotonates α to anhydride → enolate attacks PhCHO → β-elimination. Used historically to make perfume cinnamic acid. Knoevenagel reaction is similar — RCHO + active methylene (CH₂(COOR)₂, malonate) + base → α,β-unsaturated.

✔ Correct — D: Benzoin condensation: 2 PhCHO + KCN → PhCH(OH)-CO-Ph (benzoin). Mechanism: CN⁻ adds to one PhCHO → cyanohydrin → α-C is now acidic (CN stabilises carbanion) → carbanion attacks 2nd PhCHO → benzoin after proton transfer + CN⁻ leaving. Same chemistry done biologically by thiamine pyrophosphate (TPP) — C2-position carbanion as umpolung catalyst (e.g., transketolase, PDH). N-Heterocyclic carbenes (NHCs) — modern organocatalysts.

✔ Correct — C: α-Carbanion is enolate — negative charge delocalised onto carbonyl O. pKa values: aldehyde ~ 17, ketone ~ 20, ester ~ 25, amide ~ 30. 1,3-Dicarbonyls (acetylacetone, malonate, ethyl acetoacetate) have pKa 5 – 13 (two C=O stabilise via resonance) — easily deprotonated, used for many carbon-carbon bond-forming reactions (Michael, Stork enamine, malonic ester synthesis). Enolates: kinetic (LDA, low T) vs thermodynamic (NaOEt, equilibrium).

✔ Correct — B: Mannich: ketone (with α-H) + HCHO + R₂NH → R₂N-CH₂-CH₂-CO-R (Mannich base). Mechanism: amine + HCHO → iminium ion; α-C of ketone (enol) attacks iminium. Produces β-aminoketone. Mannich bases are used in synthesis of pharmaceuticals (e.g., tropicamide, tetracaine). On heating, Mannich base eliminates amine → α,β-unsaturated ketone (used to install Michael acceptor).

✔ Correct — A: Wittig (Wittig, 1954, Nobel 1979): R₃P=CR'₂ (phosphorus ylide) + R₂C=O → R₂C=CR'₂ + R₃P=O. Stabilised ylide (with EWG) → E-alkene; non-stabilised → Z-alkene; Schlosser modification → E-selectivity. Ylide preparation: R₃P + R'-X → R₃P⁺-CHR' X⁻ → BuLi/NaH → R₃P=CR'. Used in synthesis of vitamin A, carotenoids, prostaglandins. Variants: Horner-Wadsworth-Emmons (phosphonate, E-selective), Julia, Peterson olefination.

✔ Correct — C: Imine = Schiff base. Aldehyde/ketone + primary amine → carbinolamine (hemiaminal) → loses water → imine (R₂C=N-R'). Acid catalysed (mild — strong acid prevents amine from attacking; pH ~ 4 – 5 optimum). Reversible. With secondary amine (no N-H to lose), gives enamine (R₂C=CR'-NR''₂). Schiff bases are important in biochemistry (PLP-AA aldimines in transamination; rhodopsin retinal imine).

✔ Correct — A: Reformatsky reaction: BrCH₂COOR + Zn → BrZnCH₂COOR (organozinc, similar to Grignard but milder). Adds to aldehyde/ketone → β-hydroxyester. Useful when standard Grignard would react with the ester carbonyl. Modern variant: Negishi coupling uses organozinc compounds for cross-coupling. Other organometallics: organocuprates (R₂CuLi) — Gilman reagents — for 1,4-addition to enones.

✔ Correct — B: Beckmann: ketone + NH₂OH → oxime; H₂SO₄ (or PCl₅) → migration of group anti to OH → amide (1,2-shift; group migrates from C to N). Cyclohexanone oxime → caprolactam (industrial precursor of Nylon-6). Mechanism: protonation of OH → migration of anti-group → nitrilium → +H₂O → amide. Stereospecific. Other 1,2-rearrangements: Hofmann (RCONH₂ → RNH₂); Curtius (RCON₃ → RNCO); Schmidt (RCOOH + HN₃ → RNH₂ + CO₂).

✔ Correct — D: Baeyer-Villiger oxidation: R-CO-R' + R''CO₃H (peroxyacid) → R-CO-O-R' (ester). O inserts between C=O and migrating group; more substituted group migrates preferentially (migratory aptitude: H ≥ t-alkyl > cyclohexyl ≥ s-alkyl > benzyl ~ phenyl > primary alkyl > methyl). Cyclic ketones → lactones. Aldehydes → carboxylic acids (H migrates). Common reagent: mCPBA (m-chloroperbenzoic acid).

✔ Correct — A: Aliphatic acid pKa: HCOOH 3.75 (formic, strongest); CH₃COOH 4.76 (acetic); propionic 4.87; pivalic 5.0. EWG α-substituents → ↑ acidity (CCl₃COOH 0.7 ≪ CHCl₂COOH 1.3 < CH₂ClCOOH 2.86 < CH₃COOH 4.76). Aromatic acids: benzoic 4.2; o,p-NO₂-benzoic ~ 2 – 3. Aliphatic RCOOH (~ 5) is much more acidic than alcohols (~ 16) and phenols (~ 10) due to resonance stabilisation of carboxylate (two equivalent C-O bonds).

✔ Correct — C: Fischer esterification: RCOOH + R'OH ⇌ RCOOR' + H₂O (cat. H₂SO₄ or HCl; reversible). Mechanism: protonation of C=O → R'OH attacks → tetrahedral intermediate → -OH leaves as H₂O → ester. Reversibility means use excess alcohol or remove water (Dean-Stark) to drive forward. Acid chloride or anhydride is faster, irreversible alternative. Steglich esterification uses DCC + DMAP for hindered acids.

✔ Correct — B: HVZ: RCH₂COOH + Br₂ + cat. PBr₃ (or red P) → R-CHBr-COOH. Mechanism: PBr₃ converts RCOOH to RCOBr (acid bromide); RCOBr enolises easily; Br₂ brominates α-C; α-Br-RCOBr exchanges with another RCOOH → α-Br-RCOOH. α-Bromo acid is platform for α-amino acids (NH₃ → α-amino acid; Strecker synthesis is alternative) and α-OH acids.

✔ Correct — D: β-Keto acids and β-dicarboxylic acids easily decarboxylate via cyclic 6-membered TS. CH₂(COOH)₂ → CH₃COOH + CO₂ (≈ 150 °C). Acetoacetic acid (CH₃COCH₂COOH) → acetone + CO₂. This is the basis of malonic ester synthesis and acetoacetic ester synthesis (after C-alkylation, hydrolysis, decarboxylation gives substituted acetic acid or ketone respectively). Plain RCOOH doesn't decarboxylate easily (unless soda lime/NaOH/Δ).

✔ Correct — A: RCOOH + SOCl₂ → RCOCl + SO₂ + HCl. SOCl₂ is preferred — gaseous byproducts. PCl₅ → RCOCl + POCl₃ + HCl. Oxalyl chloride (COCl)₂ + DMF cat. is mild. Acid chlorides are most reactive carboxylic acid derivatives — react with: H₂O → RCOOH; ROH → ester; RNH₂ → amide; LiAlH(OtBu)₃ → aldehyde (Rosenmund: H₂/Pd-BaSO₄/quinoline); R₂CuLi → ketone.

✔ Correct — B: Acyl substitution rate determined by leaving-group stability (after tetrahedral intermediate). Reactivity: RCOCl > (RCO)₂O > RCOOR' > RCONR'₂ ≈ RCOO⁻. Conversion goes from more reactive to less (downhill in stability). Amide → acid requires harsh conditions (acid/base hydrolysis with extended heating). This order is fundamental for synthesis planning: e.g., make amide from acid chloride/anhydride/ester, but NOT from acid + amine directly (gives salt).

✔ Correct — C: Saponification: RCOOR' + NaOH → RCOO⁻Na⁺ + R'OH. Mechanism: OH⁻ attacks C=O → tetrahedral intermediate → R'O⁻ leaves → carboxylate. Irreversible (carboxylate is poor electrophile). Triglyceride + NaOH → glycerol + 3 RCOO⁻Na⁺ (soap). Saponification value (mg KOH per g of fat) inversely proportional to FA chain length. Iodine value indicates unsaturation.

✔ Correct — D: Claisen condensation: 2 RCH₂COOR' + base (NaOR') → R'CH₂CO-CR'-COOR' (β-ketoester). Mechanism: enolate of one ester attacks 2nd ester carbonyl → tetrahedral intermediate → -OR' leaves. Standard example: 2 EtOAc + NaOEt → ethyl acetoacetate (acetoacetic ester). Cross Claisen useful when one ester has no α-H (HCO₂Et + RCH₂COOR' → α-formyl ester). Dieckmann condensation = intramolecular Claisen → cyclic β-ketoester.

✔ Correct — A: Hofmann rearrangement: RCONH₂ + Br₂ + 4 NaOH → RNH₂ + Na₂CO₃ + 2 NaBr + 2 H₂O. Mechanism: N-bromination → N-bromoamide → α-deprotonation → migration of R from C to N (concerted with Br⁻ loss; RETENTION of configuration if R is chiral) → isocyanate (R-N=C=O) → hydrolysis → RNH₂ + CO₂. R loses 1 C compared to starting amide. Curtius (acyl azide → isocyanate); Schmidt (acid + HN₃) — analogous chain shortenings.

✔ Correct — C: Industrial: ketene (CH₂=C=O, from acetic acid pyrolysis at 700 °C) + AcOH → (CH₃CO)₂O. Lab: dehydrate 2 RCOOH with P₂O₅, K₂CO₃, or DCC. Acetic anhydride is a milder acetylating agent than acetyl chloride — used in aspirin synthesis (acetylation of salicylic acid -OH), heroin (diacetylation of morphine), paracetamol (N-acetylation of p-aminophenol). Acetylation of -NH₂, -OH, sugars common.

✔ Correct — A: LAH reduces -COOH → -CH₂OH (1° alcohol) via aldehyde intermediate. Strong reducing agent. NaBH₄ does NOT reduce -COOH. To stop at aldehyde, use DIBAL-H (1 equiv, -78 °C) on ester or nitrile. Other reductions: -COOR → -CH₂OH (LAH); -CONR₂ → -CH₂NR₂ (LAH); -CN → -CH₂NH₂ (LAH); RCOCl → RCHO via Rosenmund (H₂/Pd-BaSO₄/quinoline poison) or LiAlH(OtBu)₃.

✔ Correct — B: F-C acylation typically with RCOCl/AlCl₃ or (RCO)₂O/AlCl₃. Variants use carboxylic acid + Lewis acid (P₂O₅, ZnCl₂, polyphosphoric acid, or trifluoromethanesulfonic acid) — milder. ArH + AcOH/ZnCl₂ → Ar-CO-CH₃ + H₂O. Acetophenone (PhCOCH₃) is a common precursor to many pharmaceuticals (e.g., chlorothiazide, propranolol).

✔ Correct — D: See Q69. Steps: (1) Br₂ + RCONH₂ → RCONHBr; (2) Base abstracts NH-H → RCONBr⁻; (3) α-elimination → R-N=C=O (isocyanate, with R migrating, retention); (4) Hydrolysis → R-NH₂ + CO₂. Bonus rearrangements: Curtius (RCON₃ → R-NCO); Schmidt (RCOOH + HN₃ + H₂SO₄ → RNH₂); Lossen (R-CO-NH-OH ester → R-NCO). All are 1-carbon shorter primary amines.

✔ Correct — A: Curtius: acyl azide RCON₃ heated → loses N₂ + R migrates from C to N → isocyanate RNCO → +H₂O → carbamic acid → RNH₂ + CO₂. Acyl azide prepared from RCOCl + NaN₃, or RCOOH + DPPA (diphenylphosphoryl azide) + Et₃N. Total transformation: RCOOH → RNH₂ (one C lost). Compatible with mild conditions; useful in peptide synthesis. Same product as Hofmann but different intermediates.

✔ Correct — C: Fischer esterification is equilibrium; K ~ 4. To push forward: (1) excess of alcohol or RCOOH; (2) remove water (Dean-Stark with toluene azeotrope, mol sieves); (3) use anhydrous reagents. Alternative — use acid chloride or anhydride (irreversible). For ester hydrolysis, base (saponification) goes to completion (carboxylate doesn't re-react).

✔ Correct — B: Lactone = cyclic ester. β-, γ-, δ-, ε-lactones depending on ring size (4, 5, 6, 7 membered). γ- and δ- favoured. β-Lactones (4-membered) strained. Macrolide antibiotics (erythromycin, azithromycin) have large lactone rings. Penicillins/cephalosporins have β-lactam (cyclic amide). Lactam = cyclic amide; Lactim = enol form of lactam.

✔ Correct — A: Acid pKa: TFA 0.23; HCl 0.7 (in water, scaled); CCl₃COOH 0.66; oxalic 1.27, 4.27; formic 3.75; acetic 4.76; pivalic 5.0. Alkylsulfonic acids (RSO₃H) very strong (pKa ~ -3). TFA is widely used in peptide chemistry to remove Boc protecting group; in HPLC mobile phase as ion-pair reagent. Triflic acid (CF₃SO₃H, pKa -14) is among the strongest known.

✔ Correct — C: Salicylic acid (2-hydroxybenzoic acid) + acetic anhydride (acid catalysed) → aspirin (acetylsalicylic acid) + acetic acid. The phenolic -OH is acetylated. Aspirin (Bayer, 1899) is COX-1/COX-2 inhibitor (irreversible — acetylates serine residue at active site). Methyl salicylate (oil of wintergreen) — synthesised by Fischer esterification of salicylic acid with methanol.

✔ Correct — A: Soap = Na/K salt of long-chain FA (C12-C18). Hard soap (Na, solid) vs soft soap (K, liquid/paste). Made by saponification of triglyceride with NaOH/KOH. Soap forms micelles in water (hydrophilic head outside, hydrophobic tail inside) — encapsulates dirt/oil → washed away. Limitation: forms scum with hard water (Ca/Mg salts insoluble). Synthetic detergents (sodium lauryl sulfate, SDS) work in hard water (Ca/Mg salts soluble).

✔ Correct — D: Lipases hydrolyse ester bonds of triglycerides → FA + glycerol. Pancreatic lipase (with colipase + bile salts) major digestive lipase. Lipoprotein lipase (LPL) on capillary endothelium hydrolyses TG in chylomicrons/VLDL → FFA into tissue. Hormone-sensitive lipase (HSL) hormonally regulated — adipose lipolysis. Drugs targeting lipases: orlistat (pancreatic lipase inhibitor for obesity); statins indirectly affect cholesterol via HMG-CoA reductase, NOT lipase.

✔ Correct — C: In aqueous solution, basicity order is 2° > 1° > 3° > NH₃ for methylamines. Three factors interplay: +I effect of methyls (stabilises conjugate acid → favours basicity, gas-phase order is 3° > 2° > 1°), solvation of conjugate acid by H-bonding (more N-H means more H-bonds, more solvation, more basicity), and steric hindrance (3° amines: lower solvation). In water, balance favours 2°.

✔ Correct — A: Aniline pKb ~ 9.4 (much weaker base than ethylamine pKb ~ 3.4). The N lone pair is delocalised into the aromatic ring (resonance) — less available for protonation. EWG (-NO₂) makes aniline even weaker (p-nitroaniline pKb ~ 13). EDG (-OMe) increases basicity slightly. Aliphatic amine N has sp³, lone pair fully on N → more basic.

✔ Correct — B: Hofmann degradation: RCONH₂ + Br₂ + 4 NaOH → RNH₂ + Na₂CO₃ + 2 NaBr + 2 H₂O. The product amine has one fewer carbon than the starting amide. Mechanism: N-bromination → N-bromoamide → α-deprotonation → R migration from C to N → isocyanate (RNCO) → hydrolysis to amine + CO₂. R group migrates with retention of configuration (concerted).

✔ Correct — D: Gabriel synthesis: Phthalimide + KOH → potassium phthalimide; + R-X (SN2, primary halide best) → N-alkylphthalimide; + hydrolysis (or hydrazinolysis with NH₂NH₂, Ing-Manske procedure) → R-NH₂ (primary amine) + phthalhydrazide. Advantage over direct alkylation of NH₃ (which gives mixture of 1°/2°/3°/4° amines): phthalimide N has only ONE H — single alkylation possible. Doesn't work for aryl halides (no SN2).

✔ Correct — A: Acidic reduction of -NO₂ in PhNO₂ gives PhNH₂ (aniline) directly. Reagents: Sn/HCl, Fe/HCl (industrial), H₂/Pd or Pt, SnCl₂. Selective reduction conditions (intermediate isolation): Zn + NH₄Cl → phenylhydroxylamine; mild conditions → nitrosobenzene. Alkaline reduction (Zn/NaOH) gives azoxy → azo → hydrazo → amine progression.

✔ Correct — C: ArNH₂ + NaNO₂ + 2 HCl (cold, 0 – 5 °C) → ArN₂⁺Cl⁻ + NaCl + 2 H₂O. Active species: HNO₂ → NO⁺ (or H₂NO₂⁺) electrophile; attacks N → N-nitrosoamine → tautomerises → diazonium. Aromatic diazonium salts stable at low T; aliphatic diazonium → unstable, evolves N₂ instantly. Side reactions if T > 10 °C: formation of phenol from aryldiazonium + H₂O.

✔ Correct — B: Sandmeyer reaction (1884): ArN₂⁺X⁻ + CuX → Ar-X + N₂ + Cu (radical mechanism, Cu(I)/Cu(II) cycle). Variants: Gattermann (Cu/HX powder, simpler but less efficient); for ArI no Cu needed (just KI); for ArF the Schiemann reaction is used (HBF₄ → ArN₂BF₄ → Δ → ArF + N₂ + BF₃). Used as the workhorse method to make aryl halides/cyanides from amines.

✔ Correct — D: Schiemann (Balz-Schiemann) reaction: ArN₂⁺ + HBF₄ → ArN₂⁺BF₄⁻ (insoluble salt, isolable); on heating dry → ArF + N₂↑ + BF₃↑. Useful method to introduce F into aromatic ring (direct fluorination too violent). Modern alternatives: aryl boronic acid + Selectfluor; deoxofluorinations.

✔ Correct — A: ArN₂⁺ + ArOH (or ArNR₂) at slightly alkaline pH → Ar-N=N-Ar' (azo compound). Coupling occurs predominantly at para position (or ortho if para blocked). Used industrially for dyes (methyl orange — diazonium of sulfanilic acid + N,N-dimethylaniline; para red — diazonium of p-nitroaniline + 2-naphthol). Coupling is electrophilic substitution on activated aromatic ring; ArN₂⁺ is the electrophile.

✔ Correct — B: Hinsberg's test: amine + PhSO₂Cl + KOH. 1° amine: PhSO₂NHR — acidic NH (sulfonamide N-H is acidic, pKa ~ 10) → soluble in alkali → on acidification, precipitates. 2° amine: PhSO₂NR₂ — no NH → insoluble in alkali. 3° amine: doesn't react (no N-H to displace) → unreacted oily layer. Modern alternatives: NMR, IR (1°: 2 NH bands; 2°: 1 NH band; 3°: none).

✔ Correct — C: Carbylamine (Hofmann isocyanide) test: 1° amine + CHCl₃ + alcoholic KOH (heat) → R-NC (isocyanide; offensive smell — diagnostic). Mechanism: KOH + CHCl₃ → CCl₃⁻ → α-elimination → :CCl₂ (dichlorocarbene); attacks N of amine → R-NHCCl₂ → loses 2 HCl → R-N=C: (isocyanide). Specific for 1° amines only; 2° and 3° don't react.

✔ Correct — A: Aniline + HNO₂ (NaNO₂/HCl) at 0 – 5 °C → benzenediazonium chloride (C₆H₅N₂⁺Cl⁻). At higher T (> 10 °C), diazonium decomposes to phenol + N₂. Distinguishing reactions of amines with HNO₂: 1° aliphatic → unstable diazonium → rapidly decomposes to alcohol + N₂; 2° → N-nitrosoamine (yellow, oily); 3° aliphatic → no reaction (or salt); aromatic 3° (e.g., N,N-dimethylaniline) → ring p-nitrosation.

✔ Correct — D: PhNH₂ + (CH₃CO)₂O → PhNHCOCH₃ + CH₃COOH. Acetanilide is used as a protective group for aniline (deactivates amino group enough to prevent oxidation/over-reaction during EAS, while keeping it as o,p-director). After EAS (e.g., bromination), hydrolyse acetyl off to regain free amine. Acetanilide itself was an early antipyretic/analgesic (Antifebrin, 1886) — replaced by paracetamol (4-hydroxyacetanilide) due to lower toxicity.

✔ Correct — B: Aniline pKb 9.4; cyclohexylamine pKb 3.4 (~ 1 million-fold more basic). In aniline, lone pair partially delocalised into π system of ring → less available; sp² hybridisation of N (more s-character) → tighter to nucleus, less Lewis basicity; protonated anilinium loses resonance stabilisation. Cyclohexylamine has fully sp³ N with a free lone pair → much more basic.

✔ Correct — C: Diazotisation requires a primary aromatic amine (Ar-NH₂). N,N-dimethylaniline is a tertiary amine (PhNMe₂); it lacks free N-H to form diazonium. Instead, it undergoes nitrosation at the para position of the ring (electrophilic substitution by NO⁺) to give p-nitroso-N,N-dimethylaniline. Aniline, p-toluidine, sulfanilic acid all have -NH₂ → undergo standard diazotisation.

✔ Correct — A: -NH₂ is the strongest common activator, donating its lone pair into the ring by resonance (+M effect). Hence it is o,p-directing. Aniline is so reactive that bromination (Br₂ in water, no catalyst) gives 2,4,6-tribromoaniline as a white precipitate. To control to mono-bromination, protect amine as acetanilide first (acetylation reduces -NH₂ activation to moderate +M).

✔ Correct — C: Sulfanilamide (4-aminobenzenesulfonamide) — first systemic antibacterial (Domagk, 1932; Nobel 1939, prontosil). Acts as competitive inhibitor of dihydropteroate synthase (mimics PABA). Selectively kills bacteria (humans use dietary folate). Sulfonamides include sulfadiazine, sulfasalazine, sulfamethoxazole (with TMP — Bactrim/Septrin). Mechanism is exploited in folate-dependent metabolism antagonism.

✔ Correct — D: Methyl orange synthesis: sulfanilic acid (4-aminobenzenesulfonic acid) is diazotised with NaNO₂/HCl → diazonium salt; coupled with N,N-dimethylaniline (in slightly acidic to neutral medium) → orange-yellow azo compound. Acid-base indicator: red below pH 3.1 (protonated, quinoid); orange-yellow above pH 4.4 (anionic, benzenoid). Other azo dyes: para red (p-nitroaniline + 2-naphthol); congo red.

✔ Correct — A: RCN + LiAlH₄ → RCH₂NH₂ (primary amine, 4 e⁻ reduction). Useful method to make amines: alkyl halide + KCN → RCN; then LiAlH₄ → RCH₂NH₂ (chain extended by 1 C). Catalytic H₂/Raney Ni gives same product. DIBAL-H (1 equiv at low T) stops reduction at imine → on hydrolysis → aldehyde (Stephen reduction is similar — SnCl₂/HCl). H₂/Pd-C with controlled conditions: also possible.

✔ Correct — B: Sulfanilic acid (4-aminobenzenesulfonic acid) exists almost entirely as a zwitterion: amine -NH₂ deprotonates to -NH₃⁺ (basic) and sulfonic -SO₃H ionises to -SO₃⁻ (very strongly acidic, pKa ~ -3) → internal acid-base reaction. High m.p. (~ 280 °C decomp), insoluble in organic solvents, soluble in dilute alkali, sparingly in cold water. Same zwitterion concept applies to amino acids (e.g., glycine) at isoelectric pH.