COMEDK UGET Chemistry - Organic Chemistry Syllabus

What is the product of catalytic hydrogenation of alkenes and alkynes (Sabatier-Senderens)?

Alkenes add H2 (Ni/Pt/Pd catalyst) to give alkanes; alkynes add H2 to give first alkenes then alkanes. Lindlar's catalyst stops alkyne at the cis-alkene; Na/liquid NH3 gives the trans-alkene.

What is the acidic nature of terminal alkynes evidence of?

Terminal alkynes (≡C-H) have an acidic hydrogen because of the sp-hybridized carbon (50% s-character). They react with Na, ammoniacal AgNO3 (white ppt) and ammoniacal Cu2Cl2 (red ppt) - a test for terminal alkynes.

State Huckel's rule for aromaticity.

A planar, cyclic, fully conjugated ring is aromatic if it contains (4n + 2) delocalized pi electrons, where n = 0, 1, 2... (e.g. benzene has 6 pi electrons, n=1).

Name the four major electrophilic aromatic substitution reactions of benzene with their electrophiles.

Nitration (NO2+), halogenation (X+ via X2/FeX3), sulphonation (SO3/H2SO4), and Friedel-Crafts alkylation/acylation (R+/RCO+ via AlCl3).

Classify benzene substituents as ortho/para vs meta directors.

o/p-directing (mostly activating): -OH, -NH2, -OR, -R, halogens (deactivating but o/p). m-directing (deactivating): -NO2, -COOH, -CHO, -SO3H, -CN, -CONH2 (electron-withdrawing groups).

Why are halogens o/p-directing yet deactivating?

Halogens deactivate the ring by their strong -I (electron-withdrawing) effect, slowing substitution, but their lone pairs allow +R (resonance) donation that stabilizes the o/p intermediate, so they direct o/p.

State the order of reactivity of haloalkanes in SN reactions and the order of C-X bond strength.

Reactivity toward nucleophilic substitution: R-I > R-Br > R-Cl > R-F. C-X bond strength order (and bond dissociation): C-F > C-Cl > C-Br > C-I.

Compare SN1 and SN2 mechanisms.

SN1: two steps, carbocation intermediate, first-order kinetics, favoured by 3° halides and polar protic solvents, gives racemization. SN2: one step, backside attack, second-order kinetics, favoured by 1° halides and polar aprotic solvents, gives inversion (Walden).

Why are haloarenes less reactive than haloalkanes toward nucleophilic substitution?

In haloarenes the C-X bond has partial double-bond character (resonance), the carbon is sp2 (more electronegative, holds the bond tightly), and there is electronic repulsion from the ring - all making C-X stronger and substitution difficult.

What is the Wurtz-Fittig and Fittig reaction?

Wurtz-Fittig: aryl halide + alkyl halide + Na/ether → alkylbenzene. Fittig: two aryl halides + Na/ether → biaryl (e.g. biphenyl).

How does the classification of alcohols (1°, 2°, 3°) relate to the Lucas test?

Lucas reagent (conc. HCl + anhyd. ZnCl2): 3° alcohols give turbidity immediately, 2° in about 5 min, 1° show no turbidity at room temperature - distinguishing 1°, 2°, and 3° alcohols.

What are the products of oxidation of 1°, 2°, and 3° alcohols?

1° alcohol → aldehyde → carboxylic acid; 2° alcohol → ketone; 3° alcohol resists oxidation (under drastic conditions gives cleavage to smaller acids/ketones).

Why are phenols more acidic than alcohols?

The phenoxide ion formed on losing H+ is resonance-stabilized (negative charge delocalized into the ring), whereas the alkoxide ion is not. Hence phenol (pKa about 10) is far more acidic than alcohols (pKa about 16-18).

What is Williamson's ether synthesis?

Preparation of ethers (symmetrical or mixed) by reacting an alkyl halide with sodium alkoxide/phenoxide (SN2): R-O-Na + R'-X → R-O-R' + NaX. Best with primary alkyl halides.

Name the reaction: phenol + CHCl3 + NaOH → salicylaldehyde.

Reimer-Tiemann reaction - introduces a -CHO group ortho to the -OH on phenol via a dichlorocarbene intermediate.

What is Kolbe's reaction (carboxylation of phenol)?

Sodium phenoxide + CO2 under pressure, then acidification, gives salicylic acid (2-hydroxybenzoic acid). The -OH directs the -COOH to the ortho position.

Why is the carbonyl carbon of aldehydes/ketones electrophilic and which is more reactive?

The C=O is polar (O is electronegative), making carbon electron-deficient (electrophilic) toward nucleophilic addition. Aldehydes are more reactive than ketones due to less steric hindrance and less +I electron donation by alkyl groups.

Distinguish the products of aldol vs Cannizzaro reaction.

Aldol: aldehydes/ketones WITH alpha-H, in dilute base, give beta-hydroxy carbonyl (aldol). Cannizzaro: aldehydes WITHOUT alpha-H (e.g. HCHO, benzaldehyde) undergo base-induced disproportionation to an alcohol + carboxylate salt.

Which test distinguishes aldehydes from ketones?

Tollens' test (ammoniacal AgNO3 → silver mirror) and Fehling's test (red-brown Cu2O ppt) are given by aldehydes but not by ketones (aromatic aldehydes don't reduce Fehling's). Both detect the reducing -CHO group.

What is the iodoform test positive for?

Yellow ppt of iodoform (CHI3) with I2/NaOH is given by compounds containing the CH3-CO- group (methyl ketones), CH3-CH(OH)- group, acetaldehyde, and ethanol.

What is the general order of acidity of carboxylic acids vs alcohols, phenols, and water?

Carboxylic acid > phenol > water > alcohol. Carboxylic acids are strong because the carboxylate anion is resonance-stabilized over two equivalent oxygens.

How does an electron-withdrawing group affect the acid strength of a substituted acetic acid?

Electron-withdrawing groups (e.g. -Cl, -NO2) increase acidity by stabilizing the carboxylate anion via -I effect. Thus order of acidity: Cl3C-COOH > Cl2CH-COOH > ClCH2-COOH > CH3COOH.

What is the Hell-Volhard-Zelinsky (HVZ) reaction?

Carboxylic acids with an alpha-H react with Cl2/Br2 in the presence of red phosphorus to give alpha-halo carboxylic acids (alpha-chloro/bromo acids).

Classify amines and state how they are distinguished by the Hinsberg test.

Amines are 1°, 2°, or 3° (R-NH2, R2NH, R3N). Hinsberg test (benzenesulphonyl chloride): 1° amine gives a base-soluble sulphonamide, 2° gives an insoluble sulphonamide, 3° amine does not react.

Why are aliphatic amines more basic than ammonia but aromatic amines (aniline) less basic?

Alkyl groups (+I) increase electron density on N, raising basicity above ammonia. In aniline the lone pair on N is delocalized into the ring (resonance), reducing its availability, so aniline is less basic than ammonia.

What is the diazotization reaction and the diazonium salt formed?

Primary aromatic amine + NaNO2 + HCl at 0-5°C gives a benzenediazonium chloride (C6H5N2+Cl-). The low temperature is needed because diazonium salts are unstable at higher temperatures.

What is the Sandmeyer reaction?

Replacement of the diazonium group by Cl, Br, or CN using cuprous halides/cyanide: ArN2+X- + CuCl/CuBr/CuCN → ArCl/ArBr/ArCN + N2. Used to introduce halogens/CN onto an aromatic ring.

Classify carbohydrates and give an example of each.

Monosaccharides (cannot be hydrolysed, e.g. glucose, fructose), oligosaccharides (e.g. disaccharides sucrose, maltose, lactose), and polysaccharides (e.g. starch, cellulose, glycogen).

What is the difference between a peptide bond and the primary structure of a protein?

A peptide bond is the -CO-NH- amide linkage joining the -COOH of one amino acid to the -NH2 of the next. The primary structure is the specific sequence/order of amino acids joined by these peptide bonds.

Classify polymers as addition vs condensation with one example each.

Addition (chain-growth) polymers form by addition of unsaturated monomers with no loss of molecules, e.g. polythene, PVC, Teflon. Condensation (step-growth) polymers form with elimination of small molecules like water, e.g. nylon-6,6, terylene (dacron).

Classify drugs/medicines: antacids, antihistamines, antibiotics, and antiseptics with one example each.

Antacids neutralize stomach acid (e.g. ranitidine/Mg(OH)2); antihistamines (e.g. cetirizine) treat allergy; antibiotics (e.g. penicillin) kill/inhibit microbes; antiseptics (e.g. Dettol, tincture of iodine) are applied to living tissue to prevent infection.