Basic Organic Chemistry

Section 1: Introduction, Tetravalency, Hybridization & Shapes (Questions 1-10)

1. Explain the tetravalency of carbon and why carbon forms a large number of compounds. How does catenation contribute to this?
2. Describe the hybridization and shape of carbon in methane (CH₄), ethene (C₂H₄), and ethyne (C₂H₂). Draw the orbital overlap diagrams.
3. What is the hybridization of the carbon atom in (a) CO₂, (b) HCN, (c) CH₃⁺, and (d) CH₃⁻? Mention the bond angles.
4. Compare the bond lengths and bond strengths of C–C, C=C, and C≡C bonds. Why is the C≡C bond shorter than C=C?
5. Write the complete, condensed, and bond-line structural formulas for 2-methylbutane and 2,2-dimethylpropane.
6. Classify the following as primary, secondary, or tertiary carbon atoms: (a) CH₃-CH₂-CH₃, (b) (CH₃)₃C-CH₃, (c) CH₃-CH(CH₃)-CH₂-CH₃.
7. Explain why organic compounds have low melting/boiling points and are generally insoluble in water compared to inorganic compounds.
8. Draw the zigzag (sawhorse) and Newman projections for ethane. What is the most stable conformation?
9. What is a homologous series? Give the general formula for alkanes, alkenes, and alkynes. Write the first four members of the alkane series.
10. Classify the following organic compounds based on functional groups: ethanol, ethanal, ethanoic acid, chloroethane, and ethylamine.

Section 2: IUPAC Nomenclature (Questions 11-20)

11. Give the IUPAC name for: (a) CH₃-CH₂-CH(CH₃)-CH₂-CH₃, (b) (CH₃)₂C=CH₂, (c) CH₃-CH(OH)-CH₂-CH₃.
12. Write the structural formula for: (a) 3-ethyl-2-methylpentane, (b) 2,2,4-trimethylpentane, (c) pent-2-yne.
13. Name the following according to IUPAC rules: (a) CH₃-CH=CH-CH₂-CH₃ with a methyl group at position 2, (b) a compound with a longest chain of 6 carbons having a double bond and a –CHO group.
14. Identify the principal functional group and give the IUPAC name for HO-CH₂-CH₂-COOH and CH₃-CH(Cl)-CH₂-NH₂.
15. Correct the following names if wrong and give reasons: (a) 2-ethylbutane, (b) 3-methyl-2-butene, (c) 1,1-dimethylpropane.
16. Write IUPAC names for the branched chain isomers of C₅H₁₂ and C₆H₁₄.
17. Give the IUPAC name for the compound: CH₃-CH(CH₃)-CH₂-CH=CH₂.
18. Name the compound where a benzene ring is attached to –CH₂CH₂OH and explain the numbering priority.
19. What is the difference between trivial (common) and IUPAC names? Give examples for acetic acid and acetone.
20. For the compound CH₃-CH₂-CH=CH-CH₃, give both cis-trans and E/Z designations where applicable.

Section 3: Isomerism (Questions 21-30)

21. Define isomerism. Distinguish between structural isomerism and stereoisomerism with examples.
22. Give examples of chain isomerism, position isomerism, and functional group isomerism for C₄H₁₀O.
23. What is metamerism? Give an example involving ethers or ketones.
24. Explain geometrical (cis-trans) isomerism in alkenes. Why do alkenes show it but alkanes do not? Give conditions for it.
25. For but-2-ene, draw cis and trans isomers and explain which is more stable.
26. Define optical isomerism. What is a chiral carbon? Give an example of a compound showing optical activity.
27. How many structural isomers are possible for C₅H₁₂? Draw them and name them.
28. Explain tautomerism with the example of keto-enol tautomerism in acetone.
29. Identify the type of isomerism in: (a) ethanol and dimethyl ether, (b) 1-chloropropane and 2-chloropropane.
30. A compound has molecular formula C₄H₈. List all possible isomers (structural and geometrical).

Section 4: Electronic Effects, Intermediates & Reaction Mechanisms (Questions 31-45)

31. What is the inductive effect (+I and –I)? Arrange the following in decreasing order of +I effect: –CH₃, –C₂H₅, –H, –(CH₃)₂CH.
32. Explain the resonance effect with examples of +R and –R groups. Draw resonance structures for benzene and phenol.
33. What is hyperconjugation? Explain its role in the stability of alkenes and carbocations. Why is (CH₃)₃C⁺ more stable than CH₃CH₂⁺?
34. Define electromeric effect (+E and –E). How does it differ from the inductive effect?
35. Classify the following as electrophiles or nucleophiles: H⁺, Cl⁻, CH₃⁺, CN⁻, NH₃, BF₃.
36. Explain homolytic and heterolytic fission of a covalent bond. Which type produces free radicals?
37. Draw the structures and compare the stability of: (a) primary, secondary, tertiary carbocations, (b) methyl, primary, allyl, benzyl free radicals.
38. What are carbocations, carbanions, and free radicals? Arrange carbocations in order of decreasing stability: CH₃⁺, (CH₃)₂CH⁺, (CH₃)₃C⁺, CH₂=CH-CH₂⁺.
39. Identify the reaction intermediates in: (a) chlorination of methane, (b) addition of HBr to propene (Markovnikov’s rule).
40. Classify the following organic reactions: (a) CH₄ + Cl₂ → CH₃Cl + HCl, (b) CH₂=CH₂ + H₂ → CH₃CH₃, (c) dehydration of alcohol to alkene.
41. Explain substitution, addition, elimination, and rearrangement reactions with one example each.
42. In the reaction CH₃CH=CH₂ + HBr → ?, predict the major product and explain using electronic effects.
43. What is the order of stability of carbanions: CH₃⁻, CH₂=CH-CH₂⁻, C₆H₅CH₂⁻? Why?
44. Explain why phenol is more acidic than ethanol using resonance.
45. Give examples of nucleophilic substitution (SN1 and SN2) and electrophilic addition reactions.

Section 5: Purification, Qualitative & Quantitative Analysis (Questions 46-50)

46. Describe the methods for purification of organic compounds: crystallization, sublimation, distillation, and chromatography.
47. What is Lassaigne’s test? How is it used to detect nitrogen, sulfur, and halogens in organic compounds?
48. In elemental analysis, 0.5 g of an organic compound gave 0.9 g CO₂ and 0.18 g H₂O. Calculate the percentage of C and H.
49. An organic compound contains C=40%, H=6.67%, O=53.33%. Find its empirical formula. If the molecular mass is 180, find the molecular formula.
50. Explain the principles of steam distillation and fractional distillation for purification. When is each used?