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13 Dec 2019

1. When monitoring the reaction by TLC you see that the most benzaldehyde starting material has an Rf of 0.25. What should you do?

a. Use a greater amount of Ethyl Acetate in relation to the amount of Hexane until the Rf is 0.5

b. Use a greater amount of Hexane in relation to the amount of Ethyl Acetate until the Rf is 0.5

c. Rf value of 0.25 is fine as the product of this reactions the product will be more non-polar than the starting material and will travel further up the TLC plate

d. Let the TLC run longer

The NMR data giving for the product is as follows:

d 7.05 (s, 5 H), 5.95â5.30 (m, 1 H), 5.19â4.80 (m, 2 H), 4.60 (t, J = 6 Hz, 1 H), 2.44 (t, J = 6 Hz, 2 H), 2.06 (br s, 1 H).

What proton is represented at "2.06 (br s, 1 H)"?

a. Proton connected to oxygen

b. Internal proton of the alkene

c. The proton that is on the carbon alpha to the alcohol

d. This is the impurity of water in DMSO

What solvent do the authors run their NMR in?

a. CDCl3

b. d-DMSO

c. d-Acetone

d. -Benzene

The NMR data giving for the product is as follows:

d 7.05 (s, 5 H), 5.95â5.30 (m, 1 H), 5.19â4.80 (m, 2 H), 4.60 (t, J = 6 Hz, 1 H), 2.44 (t, J = 6 Hz, 2 H), 2.06 (br s, 1 H).

If you ran the NMR in d-DMSO and see an additional peak at 1.76ppm and 3.60ppm, what do these peaks represent.

a. Residue THF impurity, as THF was used as a solvent in the reaction

b. Allyl Bromide Statring Material

c. Benzaldehyde Statring Material

d. water impurity as water was used as a solvent in the reaction

e. These resonances representatives the protons of ammonium chloride which was used in the reaction

This paper states this addition of an allyl halide to a aldehyde is a "Grignard-Like" reaction. Although, traditionally reactions using allyl halides and zinc to perform carbon-carbon bond formation are known as the Barbier Reaction

a. True

b. False

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Question: For the following two experiments I have been asked to find at least 1 procedural change for each that could be made to improve the yield of my product. Please review the experiments and aid me in determining what this change might be. Thanks in advance!

Reduction of Benzophenone

1. In a 50 mL Erlenmeyer flask, dissolve 2.0 g benzophenone in 10 mL of methanol. Also add a stirbar to magnetically stir the solution.

2. Place your solution in an ice bath until the temperature has dropped to 10 C.

3. While your flask is in the ice bath, add 0.42 g of sodium borohydride, in small portions, over a 5 min period. The addition of sodium borohydride is exothermic, so you must take care to add it slowly to keep the temperature under control. This means adding the hydride in 5-6 portions, with about 1 min in between additions.

4. Once the addition of NaBH4 is complete and the vigorous bubbling has ceased, allow the solution to stir at room temperature for 10 minutes.

5. Carefully clamp the Erlenmeyer flask into a 80Â°C water bath and allow it to sit in the hot water bath for 2 minutes.

6. Remove the solution from the hot water bath and allow it to cool to room temperature and then cool it in an ice bath.

7. SLOWLY add 30 mL of cold water and then SLOWLY(dropwise) add 1.4 mL of 6M HCl. Use litmus paper to confirm that your solution is acidic. If your solution is not acidic, add more HCl until it is acidic. You should see the formation of a white precipitate at this point.

8. After adding the HCl, remove your solution from the ice bath and let it stir at room temperature for 20 minutes.

9. Collect the product by suction filtration, washing with 10-25 mL of cold water.

10. Allow the product to completely dry under suction and then record the crude weight.

11. Analyze the purity of your crude product by running a TLC. Dissolve a very small sample of your crude product and the benzophenone starting material in diethyl ether. Spot these samples on two separate lanes of your TLC place and develop the TLC pate with 9:1 petroleum ether: ethyl acetate.

12. If you are convinced that your crude sample is pure diphenylmethanol, record the final mass and run a melting point.

13. If you think some impurities are still present in your crude mixture, recrystallize your product with a minimal amount of hot hexanes. Review your notes from earlier in the semester if you donât remember the steps to run a recrystallization.

14. Record the mass and melting point of your purified diphenylmethanol and place it in a labeled vial to turn in to your instructor.

Oxidation of Diphenylmethanol

1. Place approximately 300-mL of hot (from the tap) water in a 400-mL beaker, add a boiling stone, and place it on a hot plate. Heat the water until it is 90-95 oC. It is important to keep the temperature just below 100 oC; thermal decomposition of the permanganate may occur at higher temperatures resulting in the release of toxic fumes.

2. While your water bath is heating, place 4.82 mmol of diphenylmethanol in a 10- or 25- mL round-bottomed flask.

3. Weigh out approximately 4 grams of the oxidant mixture of KMnO4/CuSO4â¢5H2O.

4. If the temperature of your water bath has reached 90-95 oC, combine the oxidant with the diphenylmethanol in your round-bottomed flask.

5. Vigorously stir the mixture with a microspatula for 5-10 min until the flask is warm to the touch. A color change from purple-blue to brown/black should be observed as you are stirring the solids. This is an indication that a reaction is occurring.

6. When the flask is warm, equip the reaction vessel with an air condenser and clamp it in the hot water bath. Be sure that the solid reaction mixture is below the surface of the water.

7. Heat the reaction for 1 h. Continue to monitor the temperature of the water; if the temperature increases close to 100 deg C, add a bit of cold water to keep the temperature 90-95 deg C and lower the heat setting on your hot plate.

8. After 1 h of heating, remove the flask from the hot water and allow it to cool to room temperature. Remove the reflux condenser.

9. Add 10 mL of hexanes to the solid and stir to mix. Remove the hexanes with a pipette and place it into a 25-mL Erlenmeyer flask. Repeat and combine the extracts.

10. Dry the combined hexane extracts with Na2SO4; decant/filter the hexanes into a preweighed 25-mL Erlenmeyer flask; and evaporate the hexanes using a gentle stream of air.

11. Analyze the purity of your crude product by running a TLC. Make samples of the following for TLC: stock benzophenone, crude benzophenone, and benzhydrol. Spot these samples on three separate lanes of your TLC place and develop the TLC pate with 5:1 hexane/ethyl acetate.

12. If you are convinced that your crude sample is pure benzophenone, record the final mass and run a melting point.

13. If you think some impurities are still present in your crude mixture OR if your product is not a solid, recrystallize your product with a minimal amount of hot methanol or methanol/water. Review your notes from earlier in the semester if you donât remember the steps to run a recrystallization.

14. Record the mass and melting point of your purified benzophenone and place it in a labeled vial to turn in to your instructor.

2.) Bart was a truly superb organic laboratory student. Unfortunately, his partner Homer was a bit careless. Bart was carefully saving solid samples of benzoic acid and ethyl-4-aminobenzoate in his lab locker; he needed to run melting point determinations on these samples after they had dried for a week. Before he got a chance, Homer picked up both samples, dumped them together in a beaker, and was about to carry them to a waste jar. Bart recovered the beaker, and decided he could easily separate the two components. How would Bart best recover the ethyl-4-aminobenzoate from the solid mixture ?

a. Dissolve the solid mixture in ether, extract the ether solution with 10% aqueous sodium hydroxide, collect the aqueous layer and add an acid.

b. Dissolve the solid mixture in ether, extract the ether solution with 10% aqueous hydrochloric acid, collect the aqueous layer and add a base.

c. Dissolve the solid mixture in ether, extract the ether solution with 10% aqueous sodium hydroxide, collect the ether layer and let the ether evaporate.

d. Dissolve the solid mixture in ether, add about the same volume of water, shake, separate and discard the aqueous layer, let the ether layer evaporate and collect the product.

3.) After Bart separated the benzoic acid + ethyl-4-aminobenzoate mixture, he recorded nujol mull IR spectra for the separated materials, as well as for some naphthalene he had in his locker. The resulting spectra are in Figure 1. Which spectrum is most likely the spectrum of benzoic acid ?

A) Fig 1-A B) Fig 1-B C) Fig 1-C D) Fig 1-D

E) None of the spectra are a good match

4. ) Bart also had vials of acetone, chloroform, and toluene which Homer dumped into another waste beaker. Bart sees no problem, he thinks he can separate this mixture also. What technique would be his best choice ?

A.) recrystallization

B.) simple distillation C

.) fractional distillation

D.) column chromatography with an alumina stationary phase

5.) If the 3-component mixture of problem 4 were injected into a gas chromatograph, which component would have the shortest retention time ? ( assume a helium carrier gas, a non-polar stationary phase, injector and t.c. detector at 150 C, column at 75 C )

A) Acetone

B) Chloroform

C) Toluene

D) There is not enough information provided.

E) The components are not likely to separate under the conditions described.

6.) Which of the following statements about the Diels-Alder reaction is FALSE ?

A) It is a [2+4] cycloaddition.

B) It is a reaction involving pi-electrons.

C) It is a concerted reaction.

D) It is a reaction favored by entropy considerations.

E) It is a thermal reaction.

7.) When the following two molecules combine by a Diels-Alder reaction, the product will contain two new sigma bonds between atoms which were not previously bonded. Between which pairs of atoms will these bond be formed ?

A) b-d and f-g

B) j-k and o-m

C) b-k and g-m

D) d-k and f-m

E) b-j and g-o

8.) Bart and Homer have returned to the lab. They are trying to run a Diels-Alder reaction, starting with 4.80 grams of cyclohexadiene (MW 80.13) and 5.88 (MW 98.06) grams of maleic anhydride. At the end of the reaction, Homer recovered 7.38 grams of the adduct, but has no idea what to report as a percent yield. Bart pulls out a calculator and quickly comes up with a number. What was the percent yield he calculated ? (Choose the closest answer, within 1 % )

A) 79.7 % B) 69.2 % C) 65.0 % D) 45.5 %

E) None of the above choices are close ( i.e. within 1% )

9.)Which of the following statements is FALSE about the experimental process used in the Diels-Alder reaction?

A) Glassware should be washed and rinsed with hot tap water immediately before adding reagents.

B) Maleic Anhydride is toxic.

C) The product may be recrystallized from the methanol solvent.

D) The I.R.'s of the product is different from maleic anhydride

E) No flames are used during this reaction.

10.) Suppose you have determined a GC spectrum for a sample oil containing an unknown diene. You are preparing to run a Diels-Alder reaction using this oil. You find 3 peaks. From determination of peak area, you find that the percent compositions represented by the peaks are: peak A is 55 percent , peak B is 30 percent, and peak C is 15 percent. The M.W. of your diene is 136 g/m. How many grams of Maleic Anhydride (M.W. 98 g/m) will you use to react with your 2.5g sample of crude diene? (The largest GC peak is the diene)

A) 0.99 B) 1.25 C)1.375 D)1.91 E)2.5

11.) In the proton NMR of ethyl acetate, which group of hydrogens would appear the most upfield ?

A. A

B. B

C. C

12.) In the proton NMR of ethyl acetate, which group of hydrogens is the most magnetically shielded?

A.) A

B.) B

C.) C

13.) Rank the proton groups of the ethyl acetate molecule in order of increasing chemical shift.

A.) BAC B.) CAB C.) ACB D.) BCA

14.) Which of the following could happen when infrared radiation is absorbed by a molecule ?

Electrons are promoted from filled to empty molecular orbitals

The orientation of a nuclear spin state changes.

Intra-molecular bond angles change

molecule begins to rotate more rapidly

molecule may glow in the dark

15.) Infrared absorption spectra of organic molecules are often presented as a plot of transmittance versus wavenumber. What is the definition of a wavenumber ?

one wavenumber = one micron

one wavenumber = one centimeter

one wavenumber = one reciprocal micron

one wavenumber = one reciprocal centimeter

wavenumber is the same as wavelength, and can be expressed in any unit of length

16.) Which bond would you expect to have the highest vibrational frequency (stretching) ?

A) Urea

B) Sodium Carbonate

C) Potassium Iodide

D) Sulfuric Acid

E) Sodium Nitrite

Questions 17 through 20 are spectra identification problems. You must identify two unknowns, referred to as compound A and compound B. Table I, attached at the end of the exam, has a list of possible compounds. Each compound listed in table I has a two digit identification code. After you have identified compound A, you will enter the first digit of its identification code as the answer for question 18, and then enter the second digit of the code as the answer for question 19. You then repeat this process for compound B in questions 20 and 21.

17.) Compound A gives a positive acetyl chloride test, and the infrared and NMR spectra are given in figures 2A thru 2C. Consult table I and the spectra, identify compound A. The first digit of the code corresponding for compound A is

A) 1 B) 2 C) 3 D) 4 E) 5

18.) The second digit of the code for compound A is

A) 1 B) 2 C) 3 D) 4 E) 5

19.) You have run a series of qualitative chemical tests on compound B, all of which came out negative. The negative chemical tests included acetyl chloride, chromic acid, potassium permanganate, silver nitrate, and 2,4-dinitrophenylhydrazine. The infrared and NMR spectra of compound B are given in the attached figures 3A thru 3C. Identify compound B. The first digit of the code in table I corresponding to compound B is

A) 1 B) 2 C) 3 D) 4 E) 5

20.) The second digit of the code for compound B is

A) 1 B) 2 C) 3 D) 4 E) 5

21.) Which of the following statements regarding Grignard reagents is FALSE ?

A. The Grignard reagent is an example of an organometallic compound.

B. Grignard reagents are stable in anhydrous ether solutions.

C. A Grignard reagent contains electrophilic carbon.

D. Once prepared , a Grignard reagent should be used quickly.

E. Grignard reagents tend to act as Bronsted bases.

22.) Suppose that in the synthesis of benzoic acid , a student uses 1.215 grams of magnesium , 7.575 grams of bromobenzene , and 22.641 grams of dry ice. If the mass of benzoic acid obtained were 4.530, what was the percent yield?

A. 32.1

B. 66.5

C. 77.0

D. 88.6

E. None of the above are correct (within 1%)

1)for this experiment, if applicable, what is the theoretical yield, balanced chemical equation, and mechanism? Please also provide a flowchart of the procedure

of the trans, trans product? Report the resuits that you obtain, including R values and the appearance ot the pots under illumination. Discard the trae n h-container desgrated for nonhalogenated waste Yield Calculation and Melting-Paint Determination. When the trans,trans-1,4-dipheny i-dry, determine the melting point [literature. 162-c} woigh the solid and 1. 3-butadi ne datormine the percentage neld it tha mening point iÂ§ below t45Â°C, recrystalizoÂ·portion of the compound from hot 95% ethanol pledatormine the meiting point Optional Exercise: Spestroscopy. Obtain the proton NMR spectrum in CDCl, or the UV spectrum in hoxane. For the UV spectrum of the product, dissolve a 10-mg sample in 100 mL of hexane in a volumetric flask Remove 10 mL. of this solution and dilute it to 100 mL in enother volurmetic flask. This concentration should be edequate for analysis. The trans trans orner nbsorbs at 328 nm and possesses fine structure., and th@ Cis.trans somer absorbs at 313 nm and has a smooth curve See d your spectrum is consistent with these observa tions Submit the spectral data with your laborstory report C. Solventiess Preparation ofReaction. Using an analytical baiance 1,4-Diphenyl-1,3-Butadiene chlonide and 850 mg of potassium phosphate (tribasic, K,PO,) and place the solids into a clean and dry 6-cm criside diameter) porcelain mortar with pour tip. Using an automatic pipet. measure and add 100 Î¼ãof cinnamaldehyde to the mixturo in the mortar Grind the mixture together for a total of 20 minutes. It is much easier to use a pestle that is long anough to grip securely in your hand, thus keeping one's fingors from getting sore or tired. At the beginning of the grindng operation, the mixture wit act lice putty and have a definite yellow coloer. Alter a feww minutes of grinding the mixture will start to turn into a thick paste that adheres to the inside of the mortar and the edges of the pestle. Bend the and of a spatula as shown in the fig ure. This bent spatula is useful for scraping the material off of the inside of the mortar and pas te and directing the mass into the center of the mortar. Repeat the scraping operation after every 1 to 2 minutes of grinding Indlude that time in the total of 20 minutes of grinding time Start Isolation of Crude 1,4-Diphenyl-1,3-Butadiene. After 20 minutes, add a few milliliters of deionized water to the material in the mortar Scrape the mortar and pestle a final time to oosen all of the product from the mortar. Pour the mixture into a Hirsch funnel inserted into a filter flask under vacuum. Use a squirt bottle with deionized water to transfer any remain- ing off-white product into the Hirsch funnel. Discard the filtrate that contains potassium phosphate and some triphenylphosphine oxide. The oft-white solid consists mainly of the trans, trans isomer, but some of the cis, trans isomer will be present as well. Crystallization. Purify the off-white solid by crystallization from absolute ethanol in a small test tube using the standard technique of adding hot solvent until the solid dissolves A small amount of impurity might not dissolve. If this is the case, use a Pasteur pipet to rap- dly remove the hot solution from the impurity and transfer the hot solution to another test tube. Cork the test tube and place it in a warm 25-mL Erienmeyer flask. Allow the solution to cool slowly. Once the test tube has cooled and crystais have formed, place the test tube in an ice bath for at least 10 minutes to complete the crystallization process. Place 2 mL of absolute ethanol in another test tube and cool the solvent in the ice bath (this solvent will be used to aid the transfer of the producti. Loosen the crystals in the test tube with a micro- spatula and pour the contents of the test tube into a Hirsch funnel under vacuum. Remove Pinkard, J. H; Wille, B,; Zechmeister, L. The Comparative Study of the Stereoisomeric 1,4-diphenyl-1, 3-butadienes.J. Am. Cheam. Sc. 1948, 70, 1938