21. Which of the following methods can prepare aldehyde in high yield from primary alcohol?
(A) Br₂, H₂O.
(B) DMSO, (COCl)₂, NEt₃/CH₂Cl₂.
(C) DIBAH.
(D) KMnO₄, HO⁻.
(E) LiAlH₄.

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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