以下 Diels-Alder 反應供第 40-41 題使用： (I) diene + dienophile (II) diene + dienophile (III) diene(MeO/MeO) + dienophile (IV) diene(MeO/OMe) + dienophile 40. Which of the Diels-Alder reactions above can not proceed?
(A) I, III
(B) I, II
(C) III, IV
(D) II, IV
(E) II, III, IV

46. What is the major product from the following reaction? (Methylcyclopentanone + H₃¹⁸O⁺ → ?, choices A-E show ¹⁸O-labeled products) (A) A (B) B (C) C (D) D (E) E

47. When an ¹⁸O-labelled ester is treated with NaOH in H₂O, carboxylic acid and alcohol are isolated. Which of the following statements is true? (¹⁸O-ester + OH⁻/H₂O → R-COOH + R’-OH) (A) ¹⁸O remains in both oxygen atoms of the carboxylic acid. (B) The solvent water should contain ¹⁸O. (C) ¹⁸O remains in the carbonyl oxygen only. (D) ¹⁸O remains in alcohol only. (E) ¹⁸O is found in both the carboxylic acid and the alcohol.

48. Which of the following is a suitable synthesis of o-methylphenol? (A) 2-chlorotoluene + KOH, 25 °C → 2-methylphenol (B) 2-aminotoluene + 1) NaNO₂, H₂SO₄, H₂O / 2) H₂O, heat → 2-methylphenol (C) toluene + heat, H₂O, H₂SO₄ → 2-methylphenol (D) 2-bromotoluene + 1) NaOAc, 25 °C / 2) NaOH, H₂O, heat → 2-methylphenol (E) toluene + 1) BH₃ / 2) NaOH, H₂O₂ → 2-methylphenol

49. What is the correct product in the following reaction? (Aniline + acid chloride/pyridine → then AlCl₃ → then H₃O⁺ → product, choices A-E are structures) (A) A (B) B (C) C (D) D (E) E

50. Which of the following reactions gives the correct product? (A) A (B) B (C) C (D) D (E) E

1. Which of the following pairs of bases lists the stronger base first? (A) F⁻ ＞ Cl⁻ (B) H₂O ＞ HO⁻ (C) HO⁻ ＞ H₂N⁻ (D) CH₃COO⁻ ＞ HO⁻ (E) H₂N⁻ ＞ CH₃COO⁻

2. Triethylamine [(CH₃CH₂)₃N] is a molecule in which the nitrogen atom is ___ hybridized and the CNC bond angle is ___ (A) sp³, 109.5° (B) sp², 109.5° (C) sp², ＜ 109.5° (D) sp³, ＜ 109.5° (E) sp, 109.5°

3. Which H atom in the molecule shown will be most readily abstracted by a bromine radical? (A) Ha (B) Hb (C) Hc (D) Hd (E) He

4. Which of the following reactive intermediates can best be described as both a nucleophile and an electrophile? (A) Carbocations (B) Carbanions (C) Carbenes (D) Free radicals (E) Alkanes

5. Are the compounds shown below best described as? (A) Cis-trans isomers (B) Constitutional isomers (C) Not isomers (D) Geometrical isomers (E) None of the above

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