FINAL EXAMINATION ANSWER KEY
Organic Chemistry 130AL
Instructor: Mouser
August 3, 1999

1. (15 points) Caryophyllene is a common contaminant present in Eugenol (when isolate from cloves using steam distillation). Outline a separation scheme for the isolation of pure dry Eugenol (use any needed solvent and reagents). Note: GC is not a practical means to purify a bulk sample.

1) Dissolve in solvent (diethyl ether or methylene chloride) +2
2) Extract organic layer with 5% NaOH +5 (+2 if NaHCO₃)
3) Isolate aqueous layer and neutralize with acid +2
4) Extract aqueous layer with diethyl ether +2
5) Dry organic layer over anhydrous Na₂SO₄ +2
6) Evaporate off diethyl ether +2

if suction filtration is mentioned, -5 points

2. (10 points) If Eugenol and water codistill at 91.6 °C at atmospheric pressure (760 mm Hg). Given that the vapor pressure of water at 91.6 °C is 560 mm Hg, calculate how many moles of Eugenol codistills with every mole of water. Show all calculations.

(760-560)/560 = 200/560 = 20/56 = 5/14; thus 5 moles Eugenol/14 mole water; or 0.357 mole of Eugenol/mole of water

3. (15 points) In the esterification reaction, an aqueous sodium bicarbonate extraction was carried out. What role(s) did the aqueous sodium bicarbonate extraction serve in the isolation of isopentyl acetate (show any appropriate reaction equations or diagrams)?

a) neutralize reaction mixture (kill the catalysis)

b) remove excess acetic acid CH₃CO₂H + NaHCO₃ --> CH₃CO₂— + CO2 (g) + H₂O

c) remove isopentyl alcohol -3 point is they show ROH going to RO^-

4. a. (6 points) If a 1.0 mL aqueous solution contained 100 mg of Compound X and was extracted with 4.0 mL of CH2Cl2, how much X would be in the organic layer?

Given: Solubility of X in water at room temperature = 100 mg/mL

Solubility of X in CH2Cl2 at room temperature = 100 mg/mL

?b.?(9 points) Would if instead, the solution was extracted with four 1.00 mL portions of CH2Cl2, how much of X would be in the combined organic layers organic layers?

5. (10 points) The melting point of an unknown compound was determined to be between 163-165 °C. The unknown was thought to be one of three known compounds which have very similar melting points. Without the aid of spectroscopic techniques (gc and TLC are also not allowed), explain how the correct compound could be simply identified. Assume all of the compounds are available).

MIXED melting Point; thus mix the unknown with a known; if the mp does not change then they are the same compounds.

6. (16 points) How many 13C{1H} NMR signals would you expect to see for the following compounds (circle your answers)?

7. (8 points) How does ¹³C and ¹³C{¹H} NMR spectroscopy differ? Explain/Demonstrate (be concise).

In ¹³C the carbon-13 coupling is observed in the form of splitting.

In ¹³C{¹H} the carbon-13 proton coupling is not observed. Thus all the signals are singlets if only protons and carbons are present.

 

8. (8 points) In ¹³C{¹H} NMR spectroscopy, what would be the multiplicity of perdeuteromethylene chloride (CD₂Cl₂) signal? Show your work for credit

I_Deuterium = 1

Thus there a 2I +1 spin states; thus three spin states which are: 1, 0, -1

1,1

1,0 and 0,1 (degenerate)

0,0 and -1,1 and 1,-1 (degenerate)

0,-1 and -1,0 (degenerate)

-1,-1

thus the carbon is split into a pentet

9. (10 points) Propose structures only for the major products A and B.

10. (8 points) Morpholine has a refractive index of 1.4534 at 20°C. What is the refractive index of morpholine at 23°C?

11. (15 points) In the esterfication experiment, after refluxing, the reaction mixture was washed with 5% sodium bicarbonate several times. This wash had a 3-fold purpose. Clearly explain why these washes were necessary.

See as answer to question #3.

12. (4 points) Which of the below statements best explains why carbon signals are singlets in 13C{1H} NMR spectroscopy (Circle).

the probability of a 13C nuclei coupling with another 13C nuclei is very unlikely

(6 points) Explain your above selection

Carbon 13 has a low natural abundance (1%), Thus the probability of finding two carbon-13s next to each other = (0.01)x(0.01)= 0.001 or 0.01% probability

13. (10 points) Below, supply a sketch of a Hirsch funnel.

See lab text

14. (18 points) Give the detailed mechanism (show all arrow pushing)for the formation of tetraphenylcyclopentadienone (aldol experiment).

15. (20 Points) Match the below IR spectra with the appropriate following compounds.

B,E,D,G

16. (15 points) Compound W has a molecular formula C₉H₈O₃. Compound W gives a positive Br₂/CCl₄ and KMnO₄ test. Compound W reacts with water yielding Compound Z. Compound Z is soluble in 5% NaOH and 5% NaHCO_3. Given the IR, ¹³C{¹H} and DEPT NMR spectrum for compound W, propose a structure for compound Z in the below provided box. [No credit will be given for structures placed outside the box.]

exo product was also given full credit