28. Which of the following carbohydrate structure is the cyclized form of the hexose in Fischer projection?

(A)
(B)
(C)
(D) 
(E)

1. Which of these dienes is the most reactive in the Diels-Alder reaction? (A) 1,3-Butadiene (B) 1,4-Pentadiene (C) 2,3-Dimethyl-1,3-butadiene (D) 1,2-Butadiene (E) 1,4-Cyclohexadiene

2. Which of the following is      not      true concerning the strength of a nucleophile? (A) Nucleophilicity may not parallel basicity. (B) Negatively charged nucleophiles are always more reactive than their conjugate acids. (C) The greater the strength of a nucleophile, the faster an Sₙ2 reaction will occur. (D) Strong bases are always good nucleophiles (E) None of these answer choices are correct.

3. Why is sodium methoxide      not      used in the Claisen condensation of ethyl acetate? (A) The methoxide is a weaker base than the ethoxide which is used. (B) sodium methoxide is more difficult to prepare than sodium ethoxide. (C) The methoxide would abstract a proton from the ethyl group of the ester. (D) Use of sodium methoxide would result in transesterification. (E) sodium methoxide can be used as well as sodium ethoxide.

4. Which of these is      not      a reversible process? (A) Base-promoted ester hydrolysis (B) Acid-catalyzed ester hydrolysis (C) Aldol addition (D) Claisen condensation (E) Acetal formation

5. A compound has the molecular formula, C₆H₁₂O₂. Its IR spectrum shows a strong absorption band near 1740 cm⁻¹; its ¹H NMR spectrum consists of two singlets, at δ 1.2 and 3.6 ppm. The most likely structure for this compound is: (A) Isopropyl propionate (B) Propyl propionate (C) Ethyl isobutyrate (D) tert-Butyl acetate (E) Methyl pivalate

6. Which of the following terms correctly describes these compounds listed below? (A) conformational isomers (B) not isomers (C) stereoisomers (D) constitutional isomers (E) enantiomers

7. Which of the following predictions of δ value and splitting pattern of the labeled protons in ¹H NMR (CDCl₃) is true? (A) Hₐ (2.5 ppm, triplet) (B) Hb (3.1 ppm, triplet of triplet) (C) Hc (3.1 ppm, triplet of triplet) (D) Hd (2.2 ppm, triplet of doublet) (E) He (2.0 ppm, singlet)

8. List of the following compounds in order of increasing reactivity in a Sₙ1 reaction. (i) MeI (ii) nBuBr (iii) tBuI (iv) iBuBr (v) iBuI (A) i ＜ ii ＜ v ＜ iv ＜ iii (B) i ＜ ii ＜ iv ＜ v ＜ iii (C) iii ＜ v ＜ iv ＜ ii ＜ i (D) iii ＜ iv ＜ v ＜ ii ＜ i (E) iii ＜ i ＜ iv ＜ ii ＜ v

9. Which of the following compound is aromatic? (A) (B) (C) (D) (E)

10. Which of the following amine can be resolved into enantiomers? (A)(B) (C) (D) (E)

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