Organic Сhemistry Exam Answers

1. Which Lewis dot structure correctly represents methane (CH₄)? Methane (CH₄) has one carbon atom and four hydrogen atoms. 7. In the Lewis structure of NO₂⁻, the formal charge on nitrogen is: Carbon has 4 valence electrons. Total electrons = 5 (N) + 12 (O₂) + 1 (extra) = 18 electrons. Structure has one N–O single bond and one N=O double bond, with resonance. Formal charge on N = –1. Each hydrogen has 1 valence electron. In the Lewis structure, carbon is in the center, forming four single bonds with four hydrogens. Structure: H–C–H (with four single C–H bonds, no lone pairs). Explanation: Carbon completes its octet (8 electrons) and each H gets 2 electrons (a duet). ✅ ✅ 8. The Lewis structure of O₃ shows: Ozone (O₃) has 18 valence electrons. Structure has one single and one double bond between oxygens, with resonance. Explanation: Two equivalent resonance forms exist, each with one O–O single and one O=O double bond. Nitrogen has 5 valence electrons. ✅ It forms 3 single bonds with hydrogen (using 3 of its electrons). 9. Which molecule’s Lewis structure violates the octet rule? ✅ Examples: BF₃, PCl₅, SF₆. Answer: BF₃ violates the octet rule — boron has only 6 electrons around it. Explanation: Boron is stable with fewer than 8 electrons. 2. In the Lewis structure of NH₃, how many lone pairs are present on nitrogen? The remaining 2 electrons form 1 lone pair. Answer: 1 lone pair on nitrogen. ✅ 3. For the molecule CO₂, which electron arrangement satisfies the octet rule? 10. In the Lewis structure of CO₃²⁻, the number of resonance structures possible is: Carbon has 4 valence electrons, and each oxygen has 6. To satisfy the octet rule, carbon must share two pairs of electrons with each oxygen. Structure: O=C=O (two double bonds). Each atom has 8 electrons in its valence shell. ✅ Carbonate ion (CO₃²⁻) = 24 electrons. It has three equivalent resonance structures with one double bond rotating among the three oxygens. Answer: 3 resonance structures. 4. In H₂O, what is the total number of valence electrons? 11. Which Lewis structure best represents the most stable form of SO₂? Hydrogen = 1 × 2 = 2 electrons Oxygen = 6 electrons Total = 8 valence electrons. Explanation: These 8 electrons are used to make two O–H bonds and two lone pairs on oxygen. ✅ SO₂ has 18 valence electrons. It has two resonance forms, each with one S=O double bond and one S–O single bond (with formal charge adjustment). Answer: Resonance hybrid of two equivalent structures with delocalized π bonds. 5. The Lewis structure of HCN shows: 12. The Lewis structure of PCl₅ demonstrates: Hydrogen (1), Carbon (4), Nitrogen (5) → total 10 electrons. Carbon forms a single bond with hydrogen and a triple bond with nitrogen. Structure: H–C≡N Explanation: Each atom gets a full octet. Phosphorus has 5 valence electrons and forms five single bonds with chlorine. Explanation: P has 10 electrons around it — expanded octet (allowed because P is in period 3). 6. Which statement about the Lewis structure of CH₃OH is correct? Usually, molecules with hydrogen bonding have the strongest forces. Answer: Molecules like H₂O, NH₃, or HF show hydrogen bonding → strongest IMF. Explanation: Due to H attached to a highly electronegative atom (O, N, or F). ✅ CH₃OH (methanol) = one C, one O, four H. Structure: C–O–H with three H bonded to C. Explanation: ✅ Carbon forms 4 bonds (3 to H, 1 to O). Oxygen forms 2 bonds (1 to C, 1 to H) and has 2 lone pairs. ✅ ✅ ✅ 13. Which molecule’s Lewis structure shows the strongest intermolecular forces? ✅ 14. In terms of Lewis structures, BF₃ is best described as: ✅ Boron forms three bonds with fluorine but has only 6 electrons. Answer: An electron-deficient molecule that violates the octet rule. Explanation: Boron is stable with 6 electrons. 23. For CH₃–C≡C–CH₂–CH₃, the correct IUPAC name is: 15. The Lewis structure of CF₄ indicates: Carbon is the center, bonded to four fluorine atoms. Each F has three lone pairs. Explanation: Carbon forms 4 single bonds, satisfying the octet for all atoms. 16. If a molecule has 24 valence electrons and 3 atoms, which could it be? ✅ Answer: pent-2-yne (often written 2-pentyne). Why: Longest chain = 5 C’s, triple bond is between C-2 and C-3 → locate as “2-yne.” 24. The general formula for alkenes is: CO₂ → 16e⁻ O₃ → 18e⁻ SO₂ → 18e⁻ Possibility: CO₃²⁻ → 24e⁻ Answer: CO₃²⁻ (carbonate ion). Answer: C H₂ . Why: One degree of unsaturation (one double bond or one ring) removes 2 H compared with the alkane formula C H₂ ₊₂. 17. Based on Lewis structures, predict which has the highest bond order: Answer: 4 carbon atoms. Why: Propene = 3 C’s, plus one methyl substituent = +1 C → total 4 C’s (also called isobutene). ✅ ✅ Compare molecules like O₂, O₂⁺, O₂⁻. Answer: O₂⁺ has the highest bond order (2.5). Explanation: Fewer electrons in antibonding orbitals → stronger bonds. 18. Which species would have the most stable Lewis structure? ✅ Species that obey the octet rule and have minimal formal charges. Example: CO₂ (all atoms have full octets and zero formal charge). 19. For a molecule with formula XH₃, if X has 5 valence electrons, the Lewis structure will show: ✅ 25. In the compound 2-methylpropene, the number of carbon atoms is: 26. Which compound would be formed by adding one carbon atom to propyne? Answer: A butyne (C₄H₆) — either 1-butyne (CH≡C–CH₂–CH₃) or 2-butyne (CH₃–C≡C–CH₃). Why: Propyne (C₃H₄) + 1 C → C₄H₆; that formula corresponds to the butyne isomers. 27. The alkane with molecular formula C₇H₁₆ is: Answer: Heptane (n-heptane is the straight-chain name). Why: Alkanes follow C H₂ ₊₂ → C₇H₁₆ is the 7-carbon alkane (many isomers possible). Like NH₃, X will form 3 single bonds with H and have 1 lone pair. Answer: XH₃ with one lone pair on X. 20. When drawing the Lewis structure for SCl₂, the most stable arrangement would show: 28. When naming CH₃–CH=CH–CH₃, the correct IUPAC name is: Sulfur = 6 valence electrons; each chlorine = 7. Answer: but-2-ene (also called 2-butene). You can specify stereochemistry as cis-2-butene / trans-2-butene or (Z)/(E). Why: 4-carbon chain, double bond between C-2 and C-3 → “2-ene.” Two Cl atoms bond with S → 2 single bonds. ✅ S has 2 lone pairs left. Answer: S in center, two single bonds to Cl, and two lone pairs on sulfur. 21. Which compound has the IUPAC name 2-methylbutane? Answer: CH₃–CH(CH₃)–CH₂–CH₃ (also called isopentane). Why: The parent chain is butane (4 C’s) and there’s a methyl group on carbon-2. 29. The compound CH₃–CH₂–C≡CH is named: Answer: but-1-yne (common name 1-butyne). Why: Number from the end nearest the triple bond so the triple is at carbon-1. 30. What is the IUPAC name for CH₃–CH₂–CH₂–CH₂–CH₃? Answer: Pentane. Why: Five carbons in a straight chain, all single bonds → pentane. 31. Which compound has the highest molecular mass? 22. The molecular formula C₄H₈ represents: Answer: An alkene or a cycloalkane (general formula C H₂ ). Why: C₄H₈ fits C H₂ , so it could be butene (e.g., CH₃–CH=CH–CH₃) or cyclobutane (a 4-membered ring). Answer (general): The one containing the heaviest atoms — e.g., a molecule with halogen(s) or oxygen(s) will weigh more than a hydrocarbon of the same C count. Example: C₄H₈Cl₂ (contains chlorine) has a higher molar mass than C₄H₁₀ (butane). Why: Atomic mass (Cl ≈ 35.5) >> H (1), so substituting H’s with heavy atoms raises molecular mass. Why: That follows IUPAC ordering and punctuation rules. 32. The correct order of increasing number of hydrogen atoms (for compounds with the same number of C) is: 39. A compound with molecular formula C₄H₆ could be: Answer: alkyne < alkene < alkane. Why: For same carbon count n: alkynes C H₂ ₋₂ (fewest H), alkenes C H₂ (middle), alkanes C H₂ ₊₂ (most H). 33. What type of compound would have the formula C₅H₈? Answer: Any structure with two degrees of unsaturation. Possibilities: a monosubstituted alkyne (one triple bond), a diene (two double bonds), or a ring + double bond (e.g., cyclobutene). Why: Degree of unsaturation = (2n+2 − H)/2 = (12 − 8)/2 = 2 → two rings/double/triple equivalents. 34. Which naming convention is correct? Answer: Several possibilities (two degrees of unsaturation): 1-butyne (one triple bond), 1,3-butadiene (two double bonds), cyclobutene (one ring + one double), etc. Why: DU = 2, so triple bond or two double bonds or ring + double are options. 40. Which represents the most complex possible structure? Answer (practical rule): The molecule that has the most branching, the most different substituents (heteroatoms), rings, and stereocenters is the most complex. For example, a highly substituted cyclic molecule with multiple functional groups and stereocenters is more complex than a straight-chain hydrocarbon of the same formula. Why: Complexity grows with structural variety (branches, rings), types of atoms, and chiral centers. Answer (key rules): 41. Which IUPAC nomenclature rule is correctly applied to name 1-methyl-2-ethylbenzene? 1. Choose the longest continuous carbon chain as the parent. Answer: The ring (benzene) is the parent structure, and substituents (methyl, ethyl) are numbered to give the lowest possible set of locants. 2. Number the chain to give the lowest set of locants for substituents and multiple bonds. Number the ring so the substituents get the smallest numbers. ✅ 3. Name substituents and list them alphabetically (ignore prefixes di-/tri- for alphabetizing). The name becomes 1-ethyl-2-methylbenzene (ethyl is named first alphabetically). Rule: Always list substituents in alphabetical order and assign the lowest numbers possible. 4. Include locants for multiple bonds (lowest possible numbers). Why: That’s IUPAC’s systematic approach for unambiguous names. 42. What determines the position numbers in naming a di-substituted benzene? Answer: The relative positions of substituents on the benzene ring. There are three basic positions: 35. For alkenes, the double bond position must be: 1,2- (ortho-) Answer: Specified with the lowest possible locant and included in the parent chain name (e.g., but-1-ene, but-2-ene). Why: The carbon numbering is chosen so the double bond gets the lowest possible number. 36. If a compound has formula C₆H₁₂, it could be: Answer: An alkene (one double bond) or a cycloalkane (one ring) — both fit C H₂ Why: One degree of unsaturation (2n vs alkane). . 1,3- (meta-) ✅ 1,4- (para-) Rule: Number the ring so substituents get the lowest possible numbers, and use o-, m-, or p- only when there are exactly two substituents. 43. In the structure C₆H₅CH₂CH₃, why is it named ethylbenzene and not phenylethane? 37. Which statement about alkynes is FALSE? Answer (example false statement): “Alkynes are saturated hydrocarbons.” — that is false. Correct fact: Alkynes are unsaturated hydrocarbons containing a carbon–carbon triple bond (each triple bond counts as two degrees of unsaturation). Answer: Benzene is treated as the main (parent) ring because it’s the dominant structure. If an alkyl chain attached to benzene has two or fewer carbons, the compound is named as an alkylbenzene (not phenylalkane). Therefore: C₆H₅CH₂CH₃ = ethylbenzene (ethyl group on benzene). ✅ 38. When naming an alkane with both methyl and ethyl substituents: 44. How would you determine the correct name for C₆H₄Br₂? Answer: Choose the longest chain as parent, number to give the lowest set of locants, and list substituents alphabetically (so ethyl comes before methyl in the name). Use commas for numbers and hyphens between numbers and words (e.g., 4-ethyl-2-methylhexane). Answer: There are three possible isomers: 1. 1,2-dibromobenzene (ortho-dibromobenzene) ✅ Explanation: The amino group is the main functional group, so “aniline” (common name) is also accepted as the IUPAC name. 2. 1,3-dibromobenzene (meta-dibromobenzene) --- ✅ 3. 1,4-dibromobenzene (para-dibromobenzene) Method: Number the ring so the bromine atoms get the lowest combination of locants. 45. What principle determines the parent chain in compounds with both aliphatic and aromatic rings? Answer: The benzene ring is usually the parent if it’s directly attached or dominates the structure. If the aliphatic chain is longer or includes a functional group (like –COOH), then the chain becomes the parent and benzene acts as a substituent (phenyl group). Rule: Choose the structure that gives the highest priority functional group as part of the parent chain. 49. How would you name a benzene ring with –Cl and –CH₂CH₃ in a 1,4-arrangement? ✅ Answer: 1-chloro-4-ethylbenzene or p-chloroethylbenzene. Explanation: Numbering gives lowest locants (1,4) and substituents are named alphabetically (chloro before ethyl). ✅ --- --- Answer: 3-methylphenol or m-cresol. Explanation: OH defines phenol as the parent, CH₃ is at the 3-position (meta to OH). 46. A compound has the structure of benzene with –CH₃ and –NO₂ groups. Which name is correct? 50. What is the correct name for C₆H₄(OH)(CH₃) with substituents in positions 1 and 3? ✅ Answer: The compound is nitrotoluene. Since –CH₃ defines toluene as the parent, and –NO₂ is the substituent, we number to give NO₂ the lowest number possible: --- Ortho-nitrotoluene (1,2-) Answer: Friedel–Crafts alkylation of benzene using ethyl chloride (C₂H₅Cl) and AlCl₃ catalyst. Reaction: C₆H₆ + C₂H₅Cl → C₆H₅C₂H₅ + HCl Explanation: Electrophilic substitution adds an ethyl group to benzene. Meta-nitrotoluene (1,3-) ✅ 51. Which reaction would produce ethylbenzene? ✅ Para-nitrotoluene (1,4-) Example: 4-nitrotoluene = p-nitrotoluene. --52. What determines the reactivity of benzene in electrophilic substitution? --47. For the compound C₆H₅COOH, which name applies? Answer: Benzoic acid. The –COOH (carboxylic acid) group has the highest priority and becomes part of the parent name, not a substituent. Explanation: “Benzene carboxylic acid” is the systematic description, but the accepted IUPAC name is benzoic acid. ✅ Answer: The electron density of the aromatic ring. Benzene’s π-electrons make it attractive to electrophiles. Substituents can activate or deactivate the ring: Electron-donating groups (–CH₃, –OH) increase reactivity. ✅ Electron-withdrawing groups (–NO₂, –COOH) decrease it. Key factor: Electron availability in the ring. --53. How does a methyl substituent affect further substitution on benzene? 48. When naming C₆H₅NH₂, which is correct? Answer: Aniline. It’s a benzene ring with an –NH₂ (amino) group directly attached. Answer: The methyl group is activating — it increases electron density by donating electrons through hyperconjugation. It also directs new substituents to the ortho and para positions. ✅ Effect: Faster reactions; favors o- and p- substitution. Nitration of benzene → nitrobenzene --Chlorination → m-chloronitrobenzene 54. Which factor most influences the orientation of incoming substituents? Then reduction → m-chlorotoluene (if CH₃ added later). Answer: The nature of existing substituents (electron-donating or withdrawing). Activating groups (e.g., –CH₃, –OH, –NH₂) → ortho/para-directing. ✅ Deactivating groups (e.g., –NO₂, –COOH, –CN) → meta-directing. Reason: Substituents alter electron density at specific positions on the ring. 55. What best explains benzene’s stability? Answer: Aromatic resonance stabilization. All six π-electrons are delocalized over six carbons in a continuous ring, forming a stable resonance hybrid. Explanation: This delocalization lowers potential energy and gives benzene extra stability (called “aromaticity”). ✅ --58. For synthesizing o-xylene, which method is most efficient? ✅ Answer: Friedel–Crafts alkylation of toluene (methylbenzene) with CH₃Cl and AlCl₃. Explanation: The existing –CH₃ group directs new substitution ortho and para → gives o-xylene and p-xylene mixture. 59. To prepare phenol from benzene, which sequence works? Answer: 56. To synthesize p-bromonitrobenzene, which sequence is most effective? 1. Nitration of benzene → nitrobenzene. Answer: 1. Nitration of benzene → nitrobenzene. 2. Reduction → aniline (C₆H₅NH₂). ✅ ✅ 3. Diazotization → benzene diazonium salt. 2. Bromination → p-bromonitrobenzene. Explanation: –NO₂ is a meta-director, but since you want the para-isomer, you start with bromobenzene first (see below). Best sequence: Brominate first (Br is ortho/para-director), then nitrate → p-bromonitrobenzene. ✅ 4. Hydrolysis → phenol (C₆H₅OH). This is the “diazonium route.” 60. Which pathway produces benzoic acid? --- ✅ Answer: Answer: Oxidation of an alkylbenzene, such as toluene. Reaction: C₆H₅CH₃ + [O] → C₆H₅COOH Explanation: Any side chain on benzene with at least one benzylic hydrogen oxidizes to benzoic acid (using KMnO₄ or K₂Cr₂O₇). 1. Nitration of toluene → mainly o- and p-nitrotoluene (since CH₃ is o,p-director). 61. In the structure of ethanol (CH₃CH₂OH), what determines its classification as a primary alcohol? ✅ In a primary alcohol, the –OH-bearing carbon is bonded to one alkyl group (or none). 57. Which reaction sequence would produce m-chlorotoluene? 2. Convert NO₂ to Cl? Not straightforward — so reverse the order: Better route: Chlorination of nitrobenzene (NO₂ is meta-director). Steps: ✅ Answer: The carbon atom bonded to the –OH group is attached to only one other carbon. Explanation: In ethanol (CH₃–CH₂–OH), the –OH is on the second carbon, which is attached to one CH₃ group → primary alcohol. ✅ Answer: Ethylene glycol (HO–CH₂–CH₂–OH). Explanation: It reacts with terephthalic acid to form polyethylene terephthalate (PET), a common polyester. ----62. What structural feature distinguishes phenol from cyclohexanol? ✅ Answer: The –OH group in phenol is attached to an aromatic (benzene) ring, while in cyclohexanol it’s attached to a saturated (non-aromatic) ring. 68. Which phenolic compound is commonly used as an antioxidant in food preservation? Explanation: Aromatic π-electrons in phenol allow resonance with –OH, making its chemistry different. ✅ Answer: Butylated hydroxyanisole (BHA) or Butylated hydroxytoluene (BHT). Explanation: These phenols prevent oxidation of fats and oils in foods. --- --- 63. When naming alcohols using IUPAC nomenclature, why is the suffix “-ol” used? 69. For disinfecting electronic equipment, which alcohol is preferred? --- --- 64. Which structural characteristic of phenol contributes to its higher acidity compared to aliphatic alcohols? 70. Which alcohol is most suitable for use in automotive antifreeze? ✅ Answer: The suffix “-ol” identifies the compound as containing a hydroxyl (–OH) functional group. Explanation: It’s added to the parent alkane name (e.g., ethane → ethanol). ✅ Answer: Resonance stabilization of the phenoxide ion. Explanation: When phenol loses a proton (H⁺), the negative charge on oxygen delocalizes into the aromatic ring, ✅ Answer: Isopropyl alcohol (2-propanol). Explanation: It cleans without leaving water residue and evaporates quickly, minimizing damage to circuits. ✅ Answer: Ethylene glycol. Explanation: It lowers the freezing point and raises the boiling point of engine coolant. making it more stable → stronger acid. 71. How would you synthesize phenol from benzene through a multi-step process? --65. Compare the hydrogen bonding ability of 1-propanol and 2-propanol. Why might their boiling points differ? ✅ Steps: ✅ Answer: Both form hydrogen bonds, but 1-propanol has a more linear structure → stronger intermolecular hydrogen bonding → higher boiling point. 1. Nitration: Benzene → nitrobenzene (HNO₃/H₂SO₄) Explanation: Branching (in 2-propanol) reduces surface contact and hydrogen bonding interactions. 2. Reduction: Nitrobenzene → aniline (C₆H₅NH₂) --- 3. Diazotization: Aniline → benzene diazonium salt (NaNO₂ + HCl, 0°C) 66. Which alcohol would be most suitable for use as a surgical antiseptic? ✅ Answer: Isopropyl alcohol (2-propanol). Explanation: It kills microorganisms effectively and evaporates quickly, leaving no residue. 4. Hydrolysis: Diazonium salt → phenol (heat with water). Explanation: This is the Hinsberg diazotization route. ----67. In the production of polyester fibers, which alcohol is commonly used? 72. Design a synthetic route to convert propene to 1-propanol: 75. Design a synthesis of ethylene glycol from ethylene: 1. Hydroboration-oxidation: 1. Epoxidation: Ethylene + O₂ → ethylene oxide. ✅ Steps: ✅ Steps: Propene + BH₃ → organoborane intermediate Oxidation with H₂O₂/NaOH → 1-propanol. Explanation: Adds –OH to the less substituted carbon (anti-Markovnikov). 2. Hydration: Ethylene oxide + H₂O → ethylene glycol. Explanation: This is the commercial process for antifreeze production. ----73. Propose a method to convert ethanol to phenol: ✅ Steps: 1. Ethanol → Ethyl chloride (CH₃CH₂Cl) by reaction with HCl. 76. Evaluate the effectiveness of different alcohols as fuel additives: ✅ Answer: Methanol & Ethanol: Most effective → increase octane, reduce CO emissions. Isopropanol & Butanol: Higher energy content but less miscible with gasoline. Conclusion: Ethanol is most commonly used for its balance of energy, safety, and availability. 2. Ethyl chloride → Benzene (C₆H₆) by catalytic reforming or dehydrogenation. --3. Benzene → Phenol by the diazonium route (as in Q71). Explanation: Multi-step industrial synthesis via benzene intermediate. 77. Assess the environmental impact of phenol production methods: ✅ Answer: Traditional routes (cumene process) produce waste (acetone, acids). --74. How would you synthesize 2-methyl-2-propanol from propene? Modern green methods use biocatalysts or direct oxidation of benzene → less pollution. Conclusion: Environmental impact depends on waste management and energy use in production. 1. Addition of H₂O (hydration) using H₂SO₄ catalyst → 2-propanol intermediate. --- ✅ Steps: 78. Which factor most significantly influences the industrial choice of alcohol production method? 2. Isomerization and alkylation with methyl groups → tert-butanol (2-methyl-2-propanol). Simpler lab route: Propene + H₂O (acid-catalyzed) in the presence of tertiary carbocation rearrangement. ✅ Answer: Cost and availability of raw materials. Explanation: Industries prefer routes using cheap, abundant feedstocks (e.g., fermentation for ethanol, hydration of ethene for industrial ethanol). --- --- 79. Evaluate the most critical factor in choosing an alcohol-based solvent for pharmaceutical production: ✅ Answer: Purity and toxicity. Explanation: Solvents must dissolve active ingredients efficiently but also be non-toxic, stable, and easy to remove 88. Which solvent would be most appropriate for Williamson ether synthesis? from the final product. ✅ Answer: Polar aprotic solvents like DMSO, acetone, or DMF. Explanation: They enhance nucleophilicity of the alkoxide and suppress elimination. 80. Assess the most important consideration when selecting a phenolic preservative for food products: 89. To prepare an epoxide from an alkene, which reagent should be used? ✅ Answer: Safety and stability. Explanation: It must inhibit oxidation and microbial growth without harming human health or altering food flavor. ✅ Answer: Peroxy acids such as mCPBA (meta-chloroperoxybenzoic acid) or H₂O₂. Reaction: Alkene + peracid → epoxide + acid. 81. Which statement correctly explains the Williamson ether synthesis? ✅ Answer: It is the reaction of an alkoxide ion (RO⁻) with a primary alkyl halide (R’–X) to form an ether (R–O–R’). Example: CH₃ONa + CH₃CH₂Br → CH₃OCH₂CH₃ (ethyl methyl ether). Mechanism: SN2 nucleophilic substitution. 90. In the industrial production of MTBE (methyl tert-butyl ether), what temperature range is typically used? ✅ Answer: 30–90°C. Explanation: Reaction between isobutene and methanol is exothermic and favored at moderate temperatures. 82. What is the primary factor affecting the rate of nucleophilic substitution in ether synthesis? ✅ Answer: The structure of the alkyl halide — primary halides react fastest. Explanation: Secondary and tertiary halides undergo elimination instead of substitution due to steric hindrance. 91. Which method would be most efficient for preparing a large-scale batch of diethyl ether? ✅ Answer: Acid-catalyzed dehydration of ethanol at ~140°C using H₂SO₄. Explanation: Simple, inexpensive, and suitable for bulk production. 83. Why are ethers less reactive than alcohols? ✅ Answer: Ethers lack the –OH hydrogen, so they cannot form hydrogen bonds or undergo oxidation easily. Explanation: Their oxygen is already bonded to two carbons → less reactive toward acids and bases. 84. What determines the regioselectivity in epoxide ring opening? ✅ Answer: The reaction conditions: Under acidic conditions, attack occurs at the more substituted carbon. Under basic conditions, attack occurs at the less substituted carbon. Explanation: Depends on charge distribution and steric effects. 92. What is the best way to prevent side reactions in Williamson ether synthesis? ✅ Answer: Use a primary alkyl halide and maintain mild conditions to avoid elimination (E2) side reactions. Explanation: Avoid secondary/tertiary halides which form alkenes instead of ethers. 93. Which statement best explains why ethers are used as solvents in organic reactions? ✅ Answer: Ethers are chemically inert, polar enough to dissolve organic molecules, and have low boiling points, making them easy to remove. Example: Diethyl ether, THF. 94. What is the primary advantage of using epoxides in polymer synthesis? 85. How does the presence of an acid catalyst affect ether formation? ✅ Answer: Epoxides are highly reactive and can open their ring to form long polymer chains (polyethers). Explanation: Strain in the three-membered ring drives polymerization. Example: 2CH₃CH₂OH + H₂SO₄ → CH₃CH₂–O–CH₂CH₃ + H₂O. 95. Why are cyclic ethers more reactive than acyclic ethers? ✅ Answer: The acid protonates the alcohol, forming a better leaving group, which speeds up condensation (dehydration) to form ethers. 86. A chemist wants to synthesize methyl ethyl ether. Which reagents should they use? ✅ Answer: Sodium methoxide (CH₃ONa) + ethyl bromide (C₂H₅Br). Reaction: CH₃ONa + C₂H₅Br → CH₃–O–C₂H₅ + NaBr. Explanation: Williamson ether synthesis using a primary halide. 87. In the production of diethyl ether, what temperature condition is most appropriate? ✅ Answer: Around 140°C (using concentrated H₂SO₄). Explanation: Below 140°C → ether formation; above 170°C → dehydration to ethene. ✅ Answer: Ring strain. Explanation: Small rings like epoxides have angle strain (~60°), making them much more reactive to nucleophilic attack. 96. A researcher needs to design a new method for ether synthesis. Which approach would be most innovative? ✅ Answer: A green catalytic method using enzymes or heterogeneous catalysts under mild conditions with no halogen waste. Example: Direct coupling of alcohols using metal catalysts (e.g., Cu, Pd). 97. In developing a new pharmaceutical containing an ether linkage, which synthetic route would be most suitable? ✅ Answer: Williamson ether synthesis using mild, selective conditions to avoid affecting sensitive functional groups. Explanation: Allows control over substitution and functional group tolerance. 98. For a large-scale industrial process, which factor would be most critical in choosing an ether synthesis method? ✅ Answer: Safety, cost, and scalability. Explanation: The process must minimize hazards (explosion risk), handle large volumes, and use inexpensive reagents. 99. In designing a biodegradable polymer, which type of ether linkage would be most appropriate? ✅ Answer: Poly(ether-ester) or polyethylene glycol (PEG)-type linkages. Explanation: These bonds are stable in use but hydrolyze under environmental conditions, aiding biodegradability. 100. For a green chemistry approach to ether synthesis, which modification would be most effective? ✅ Answer: Use of renewable alcohol feedstocks and solid acid catalysts instead of strong liquid acids or halides. Explanation: Reduces toxic waste, improves energy efficiency, and promotes sustainability.