JEE Advanced Organic Chemistry Flashcards

24 sample cards from the Organic Chemistry deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. How are alcohols classified and how does Lucas reagent distinguish them?

   Alcohols are 1°, 2°, or 3° by the carbon bearing -OH. Lucas reagent (conc. HCl + anhydrous ZnCl2): 3° reacts immediately (turbidity at once), 2° in about 5 min, 1° no reaction at room temperature.

2. What is the Williamson ether synthesis and why does it favor 1° halides?

   Sodium alkoxide + alkyl halide -> ether (SN2). It works best with 1° (or methyl) halides; 2°/3° halides undergo elimination to alkenes instead because alkoxides are strong bases.

3. How does the acidity of phenol compare to alcohols and carboxylic acids, and why?

   Acidity: carboxylic acid > phenol > water > alcohol. Phenol is more acidic than alcohols because the phenoxide ion is resonance-stabilized; it is less acidic than carboxylic acids because the carboxylate has more effective (equivalent) resonance.

4. Name the reactions: Reimer-Tiemann, Kolbe, and Williamson as applied to phenol.

   Reimer-Tiemann: phenol + CHCl3 + NaOH -> salicylaldehyde (ortho -CHO). Kolbe (Kolbe-Schmitt): sodium phenoxide + CO2 (under pressure) then H+ -> salicylic acid. Williamson: sodium phenoxide + RX -> aryl alkyl ether.

5. What products result from dehydration of alcohols and what is the order of ease?

   Dehydration with conc. H2SO4 (or Al2O3 heat) gives alkenes (Saytzeff product) via E1. Ease of dehydration: 3° > 2° > 1° (more stable carbocation forms more readily).

6. Compare reactivity of aldehydes vs ketones toward nucleophilic addition and explain.

   Aldehydes are more reactive than ketones because they have less steric hindrance and less electron-donating (+I/hyperconjugation) alkyl groups, so the carbonyl carbon is more electrophilic.

7. What is the aldol condensation and which carbonyl compounds undergo it?

   Aldol condensation: two carbonyl molecules with at least one alpha-hydrogen react under dilute base/acid; one acts as a nucleophilic enolate adding to the other's carbonyl to give a beta-hydroxy carbonyl (aldol), which can dehydrate to an alpha,beta-unsaturated carbonyl.

8. What is the Cannizzaro reaction and which aldehydes undergo it?

   Cannizzaro: aldehydes with NO alpha-hydrogen (e.g., HCHO, benzaldehyde) undergo base-induced disproportionation, giving an alcohol and a carboxylate salt (one molecule oxidized, one reduced).

9. Name two tests that distinguish aldehydes from ketones.

   Tollens' test (ammoniacal AgNO3): aldehydes give a silver mirror, ketones do not. Fehling's/Benedict's test: aliphatic aldehydes give a red Cu2O precipitate; ketones (and aromatic aldehydes) do not.

10. What is the iodoform reaction and which compounds give a positive test?

    Treatment with I2/NaOH (or NaOI) gives yellow CHI3 (iodoform). Positive for methyl ketones (CH3CO-), acetaldehyde, and alcohols oxidizable to them (CH3CH(OH)- groups), e.g., ethanol, isopropanol.

11. State the order of acidic strength among substituted acetic acids: ClCH2COOH, CH3COOH, Cl3CCOOH, Cl2CHCOOH.

    Cl3C-COOH > Cl2CH-COOH > ClCH2-COOH > CH3-COOH. More electron-withdrawing -Cl atoms (-I effect) stabilize the carboxylate and increase acidity.

12. List the carboxylic acid derivatives in order of decreasing reactivity toward nucleophilic acyl substitution.

    Acid chloride > acid anhydride > ester > amide. Reactivity decreases as the leaving group becomes worse and as electron donation into the carbonyl increases.

13. What is the Hofmann bromamide degradation and its synthetic use?

    A primary amide reacts with Br2 and aqueous NaOH/KOH to give a primary amine with ONE fewer carbon (RCONH2 -> RNH2). It is used to step down a carbon chain and prepare 1° amines.

14. How do you distinguish 1°, 2°, and 3° amines using the Hinsberg test?

    With benzenesulfonyl chloride (Hinsberg reagent): 1° amines give a sulfonamide soluble in alkali (N-H still acidic); 2° amines give a sulfonamide insoluble in alkali; 3° amines do not react (no N-H).

15. What is the carbylamine (isocyanide) test and what does it identify?

    Primary amines (and only 1° amines) heated with chloroform and alcoholic KOH give foul-smelling isocyanides (carbylamines): RNH2 + CHCl3 + 3KOH -> RNC + 3KCl + 3H2O. It is a test for primary amines.

16. Why is aniline a weaker base than aliphatic amines, and how does it react with nitrous acid?

    In aniline the lone pair on N is delocalized into the benzene ring (resonance), reducing availability for protonation, so it is a weaker base. With HNO2 (NaNO2 + HCl) at 0-5°C, aniline forms a stable benzenediazonium salt used in coupling and substitution reactions.

17. Classify carbohydrates and give the glycosidic linkage in maltose, sucrose, and lactose.

    Carbohydrates: monosaccharides (glucose, fructose), oligosaccharides (disaccharides), polysaccharides (starch, cellulose). Maltose = glucose + glucose (alpha-1,4); Sucrose = glucose + fructose (alpha-1,2, non-reducing); Lactose = galactose + glucose (beta-1,4).

18. What is the difference between a reducing and non-reducing sugar, and is sucrose reducing?

    A reducing sugar has a free aldehyde/ketone (or free anomeric -OH) and reduces Tollens'/Fehling's. Sucrose is non-reducing because both anomeric carbons are involved in the glycosidic bond. Glucose, fructose, maltose, and lactose are reducing.

19. Define the peptide bond and the zwitterion form of an amino acid.

    A peptide bond is an amide (-CO-NH-) linkage formed between the -COOH of one amino acid and the -NH2 of another with loss of water. In solution amino acids exist as zwitterions (+H3N-CHR-COO-), dipolar ions, neutral overall at the isoelectric point.

20. Differentiate addition (chain-growth) and condensation (step-growth) polymers with one example each.

    Addition polymers form by repeated addition of monomers (usually with C=C) without loss of any molecule, e.g., polythene from ethene. Condensation polymers form by repeated condensation between bifunctional monomers with loss of small molecules (H2O, etc.), e.g., nylon-6,6, terylene.

21. Give the monomers of nylon-6,6, terylene (Dacron), and bakelite.

    Nylon-6,6: hexamethylenediamine + adipic acid. Terylene/Dacron (PET): ethylene glycol + terephthalic acid. Bakelite: phenol + formaldehyde.

22. In qualitative organic analysis, what does Lassaigne's test detect and how is nitrogen detected?

    Lassaigne's (sodium fusion) test detects N, S, and halogens by fusing the compound with Na to form ionic NaCN, Na2S, NaX. Nitrogen is confirmed by forming Prussian blue (ferric ferrocyanide) when the extract is treated with FeSO4 and then acid.

23. How are sulphur and halogens detected in Lassaigne's extract?

    Sulphur: sodium nitroprusside gives a violet/purple color (Na2S), or lead acetate gives a black PbS precipitate. Halogens: acidify the extract with dilute HNO3 (boil to remove CN-/S2-), add AgNO3 — white ppt (Cl, soluble in NH3), pale yellow (Br), yellow (I).

24. How is the percentage of nitrogen estimated by the Kjeldahl method, and what is its limitation?

    Kjeldahl: the compound is digested with conc. H2SO4 (N -> (NH4)2SO4), liberated NH3 by NaOH is distilled into a known excess of standard acid, and back-titrated; %N = (1.4 x N(acid) x V)/mass. It fails for N in rings (pyridine), azo, nitro, and -N=N- groups.

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