Organic Chemistry Ⅰ 2nd Examination

Dec. 13, 2003 9:00 a.m.-11:00 a.m.

Ⅰ. Each of the following problems has five statements. Each problem is worth four points. Any wrong guess will cost you one extra point. (60 points)

1. How many stereoisomers (enantiomers and diastereomers, if any) of the following are possible?

OOOH HO

HHO OH

H

(A) 2 (B) 3 (C) 4 (D) 5 (E) 6

2. The molecular formulas and 13C NMR chemical shifts (in ppm) of a hydrocarbon are given below. The splitting pattern of each signal, taken from the non-decoupled spectrum is given in parentheses. What is the structure?

(Hint: “t” means the 13C signal splits into a triplet due to coupling with the two H nuclei. “d” means doublet.)

C7H10: 25.2 (t), 41.9 (d), 48.5 (t), 135.2 (d)

(A) (B) (C)

(D) (E)

3. Indicate the reagents required to achieve the following transformation:

HCH3

Br

CH3

CH3O HH

CH3CN

CH3

CH3O H?

(A) NaCN

(B)

1) NaF2) KCN (C)

(D)

1) NaI

2) NaCN (E)

1) NaOMe

2) HCN / light

4. An unknown compound has been isolated in pure form and found to exhibit []D = + 15∘ (c = 4 g/ml, CH2Cl2). Which of the following might be the structure of the compound?

(A) (B)

(C) (D)

(E)

5. Which of the haloalkanes below would you expect to exhibit the fastest rate of the

following solvolysis reaction?

RX ROH + HX H2O acetone

(A) CH3CH2Br (B) CH3Br (C) (CH3)3CBr

(D) CH3CHBrCH3 (E)

Br

6. Name the following compound:

Cl

Br

(A) (1S, 2S, 5R)-1-bromo-2-isopropyl-5-chlorocyclohexane(B) (1R, 2R, 5R)-1-bromo-2-isopropyl-5-chlorocyclohexane(C) (1S, 3S, 4R)-1-chloro-3-bromo-4-isopropylcyclohexane(D) (1R, 2S, 4R)-2-bromo-4-chloro-1-isopropylcyclohexane(E) (1S, 2S, 4R)-2-bromo-4-chloro-1-isopropylcyclohexane

7. The molecular formulas and 13C NMR chemical shifts (in ppm) are given below. The splitting pattern of each signal, taken from the non-decoupled spectrum is given in parentheses. What is the structure?

C4H6O: 18.2 (q), 134.9 (d), 153.7 (d), 193.4 (d)

(A)

O

(B)

O

(C)

O

(D) H

O

(E) H

O

8. A bottle was labeled simply "dibromodichlorobenzene" without specifying which

isomer was present. Capillary GC showed that it was a single pure compound, and the proton decoupled carbon NMR spectrum showed FOUR peaks (not including solvent). You can conclude that the bottle contained

(A) (B) (C)

(D) (E)

9. Indicate the expected MAJOR product of the following reaction:

CH3

CH3

Cl NaOEt?

(A) (B) (C)

(D) (E)

10. Which of the following molecules have the S configuration?

H

BrH3C

F

(CH3)3CH

H

iso-propylH3C

EtD

BrH

I II III IV

(A) I, II(B) I, III(C) III, IV(D) I, II, IV(E) all of them

11. Which of the bases below would be best to accomplish the following reaction?

CH2 CH2 CH2Br CH2 CH CH2

?

(A) CH3O- Na+ (B) CH3CH2O- Na+

(C) (CH3)2CHO- Na+

(D) (CH3)3CO- Na+ (E) Na+ -OH

12. Which compound C9H11Br would give the proton NMR spectrum shown below?

(A)

CH2 CH CH3

Br

(B) Br

CH2CH2CH3

(C)

CH CH2CH3

Br

(D) Br

CH2CH2CH3

(E)

CH CH2BrCH3

13. Which of the following compounds is consistent with the proton NMR spectrum

shown below?

(A) (B) (C)

(D) (E)

Use the following box to answer questions 14-15

14. How many pair(s) of enantiomer(s) is (are) there in above five compounds?(A) 0(B) 1(C) 2 (D) 3(E) 4

15. How many pair(s) is (are) the diastereomer(s)?(A) 0(B) 1(C) 2(D) 3(E) 4

Ⅱ. Answer the following team problems: (50pts)

1. Find all chiral molecules of the molecular formula C4H7Cl. (6 pts)

2. (a). Menthyl chloride reacts with sodium ethoxide in ethyl alcohol to give a single product as shown. Analyze this reaction mechanistically to explain why this is the only alkene produced. (4 pts)

By contrast, neomenthyl chloride is treated in the same fashion give to a mixture of products shown below. Moreover, menthyl chloride reacts much more slowlythan neomenthyl chloride. Explain these observations mechanistically. (5 pts)

(b). When menthyl chloride is treated under solvolytic conditions with 80%aqueous ethyl alcohol, once again, two products are formed in the ratioshown below. Explain mechanistically. (5 pts)

3. Chlorocyclohexane reacts with sodium cyanide (NaCN) in ethanol to givecyanocyclohexane. The rate of formation of cyanocyclohexane increases when a

small amount of sodium iodide is added to the solution. Explain this acceleration in the rate. (6 pts)

4. 2-Bromo, 2-chloro, and 2-iodo-2-methylbutanes react at different rates with puremethanol but all produce 2-methoxy-2-methylbutane, 2-methyl-1-butene and 2-methyl-2-butene of same ratio. Explain these results in terms of reaction mechanism. (6 pts)

5. Consider the following reaction and propose a reasonable mechanism. (6 pts)

6. (a) Please propose a reasonable structure for the following spectra. You have to describle how you obtain your answer. (5 pts)

(b). The molecular structure and 1H-NMR spectrum (in ppm) is shown below. This

spectrum is measured by Brucker-300MHz machine. The expanded region fromδ 5.0-6.5 in shown at the end of page. Try to analysis it by giving the

chemicalshifts for protons, Ha, Hb, and Hc, and calculate the coupling constants. Pleaseround off figures after decimal point. (7 pts)