KEAM 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. Classify alcohols as primary, secondary, and tertiary.

   Based on the carbon bearing -OH: primary (1°) -OH on a carbon attached to one other C, secondary (2°) to two, tertiary (3°) to three carbons. They differ in oxidation behaviour and Lucas test response.

2. What is the Lucas test and how does it distinguish 1°, 2°, 3° alcohols?

   Lucas reagent (conc. HCl + anhydrous ZnCl2) gives turbidity. 3° alcohol: immediate turbidity; 2°: turbidity in about 5 min; 1°: no turbidity at room temperature (only on heating).

3. How are phenols more acidic than alcohols?

   Phenoxide ion is stabilised by resonance (negative charge delocalised over the ring), so phenols (pKa about 10) are far more acidic than alcohols (pKa about 16). Electron-withdrawing groups increase phenol acidity.

4. What is Williamson's ether synthesis?

   An alkyl halide reacts with sodium alkoxide/phenoxide to form an ether (SN2): R-ONa + R'-X → R-O-R' + NaX. Best with primary alkyl halides to avoid elimination.

5. What is Kolbe's reaction (Kolbe-Schmitt)?

   Sodium phenoxide is treated with CO2 under pressure followed by acidification to give salicylic acid (ortho-hydroxybenzoic acid). It is an electrophilic substitution by carbon dioxide.

6. What is Reimer-Tiemann reaction?

   Phenol treated with CHCl3 and aqueous NaOH, then hydrolysed, introduces a -CHO group at the ortho position giving salicylaldehyde. The electrophile is dichlorocarbene (:CCl2).

7. Give the general formulas/structures of aldehydes, ketones, and carboxylic acids.

   Aldehyde: R-CHO (carbonyl at chain end). Ketone: R-CO-R' (carbonyl between two carbons). Carboxylic acid: R-COOH (carboxyl group).

8. Why are aldehydes more reactive than ketones toward nucleophilic addition?

   Aldehydes have less steric hindrance and only one electron-donating (+I) alkyl group, leaving the carbonyl carbon more electrophilic. Ketones have two +I alkyl groups that reduce electrophilicity and add steric bulk.

9. How do Tollens' and Fehling's tests distinguish aldehydes from ketones?

   Aldehydes reduce Tollens' reagent (ammoniacal AgNO3) to a silver mirror and reduce Fehling's solution to a red Cu2O precipitate. Ketones give negative results (aromatic aldehydes don't respond to Fehling's).

10. What is the Cannizzaro reaction?

    Aldehydes lacking an alpha-hydrogen (e.g., HCHO, benzaldehyde) undergo disproportionation with concentrated NaOH: one molecule is oxidised to a carboxylate and another reduced to an alcohol.

11. What is the aldol condensation?

    Aldehydes/ketones with alpha-hydrogens react in dilute base to give a beta-hydroxy aldehyde/ketone (aldol), which on heating loses water to form an alpha,beta-unsaturated carbonyl compound.

12. What is the Clemmensen and Wolff-Kishner reduction?

    Both reduce C=O to CH2. Clemmensen uses Zn-Hg/conc. HCl (acidic). Wolff-Kishner uses NH2-NH2 then KOH/ethylene glycol heat (basic). Used to convert aldehydes/ketones to hydrocarbons.

13. Why are carboxylic acids more acidic than phenols and alcohols?

    The carboxylate ion is resonance-stabilised by two equivalent oxygen atoms sharing the negative charge equally, making carboxylic acids (pKa about 4-5) stronger acids than phenols and alcohols.

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

    Carboxylic acids with an alpha-hydrogen react with Cl2/Br2 in the presence of red phosphorus to give alpha-halo carboxylic acids.

15. Classify amines as primary, secondary, and tertiary and give the test to distinguish them.

    1°: R-NH2, 2°: R2NH, 3°: R3N (based on H atoms replaced on N). Hinsberg's test (benzenesulphonyl chloride) distinguishes them; also carbylamine test is positive only for 1° amines.

16. What is the carbylamine (isocyanide) test?

    Primary amines (aliphatic or aromatic) heated with chloroform and alcoholic KOH give foul-smelling isocyanides (carbylamines). Secondary and tertiary amines give no reaction. It is a test for 1° amines.

17. How is a diazonium salt prepared and why is it important?

    Aromatic primary amine + HNO2 (NaNO2 + HCl) at 0-5°C gives aryl diazonium salt (ArN2+Cl-). It is a versatile intermediate for replacing -N2+ with -Cl, -Br, -I, -CN, -OH, -H, or coupling to make azo dyes.

18. What is the basicity order of amines in the gas phase vs aqueous medium?

    Gas phase: 3° > 2° > 1° > NH3 (inductive only). In water, aliphatic 2° amines are often most basic due to a balance of inductive, steric, and solvation effects. Aromatic amines are weaker bases than ammonia.

19. Classify carbohydrates into monosaccharides, oligosaccharides, and polysaccharides.

    Monosaccharides cannot be hydrolysed (e.g., glucose, fructose). Oligosaccharides give 2-10 monosaccharides on hydrolysis (e.g., sucrose, maltose). Polysaccharides give many (e.g., starch, cellulose, glycogen).

20. Differentiate reducing and non-reducing sugars with examples.

    Reducing sugars have a free aldehyde/ketone group and reduce Tollens'/Fehling's (e.g., glucose, fructose, maltose, lactose). Non-reducing sugars lack a free group (e.g., sucrose, which is glucose+fructose linked through both anomeric carbons).

21. What is the difference between alpha-helix and beta-pleated sheet in proteins?

    Both are secondary structures stabilised by hydrogen bonds. In the alpha-helix the polypeptide coils into a right-handed spiral; in the beta-pleated sheet chains lie side by side in zig-zag sheets.

22. Name the building blocks of nucleic acids and the bases in DNA vs RNA.

    A nucleotide = base + pentose sugar + phosphate. DNA: deoxyribose; bases A, G, C, T. RNA: ribose; bases A, G, C, U (uracil replaces thymine).

23. Differentiate addition and condensation polymers with examples.

    Addition polymers form by repeated addition of unsaturated monomers with no by-product (e.g., polythene, PVC, Teflon). Condensation polymers form by repeated condensation of bifunctional monomers losing small molecules like water (e.g., nylon-6,6, terylene, bakelite).

24. Classify drugs (chemicals in medicine) by their action: antacids, antihistamines, and antibiotics with one example each.

    Antacids neutralise stomach acid (e.g., ranitidine, omeprazole). Antihistamines block histamine for allergies (e.g., cetirizine). Antibiotics kill/inhibit microbes (e.g., penicillin, chloramphenicol).

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