Experiment 1 Post-Lab 1 PDF

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Saleana Caraballo CHM-2021-02

Experiment 1 Post-Lab Assignment Instructions: This post-lab assignment is due by the start of your lab section during the week of February 1518. A completed copy of this post-lab assignment should be submitted to Blackboard.

Alcohol Oxidations – Beyond Labz 1. The procedure mentions that the starting amount of benzyl alcohol is 3.00 mL. How many moles does 3.00 mL of benzyl alcohol contain? If 3.00 mL of benzyl alcohol reacts with enough of the appropriate oxidizing agent, calculate the theoretical yield of the benzoic acid product. Show calculation with units for full credit. The amount of moles that is contained in 3.00 mL of benzyl alcohol is 0.028 moles.

3.00 g benzyl alcohol ×

1mol benzyl alcohol =0.02774 mol benzyl alcohol 108.14 g/mol

0.02774 mol benz oic acid ×

122.12 g =3.3876 g benzoic acid 1 mol benzoic acid

theoretical yield=3.39 g benzoic acid

Part 1 Results (Failed Experiment) 2. Describe what went wrong with this trial. Why did it happen? How can this problem be corrected? The flask containing the reaction exploded during the reaction. This happened because of the amount of pressure building up in the flask throughout the reaction and evaporation. The amount of particles in the flask increased as the reaction continued and so did the pressure causing the flask to explode. This combined with the heat applied to the flask caused it to shatter. This problem can be corrected by using a reflux condenser to prevent the solvent from evaporating and adding a nitrogen line to the top of the condenser.

Part 2 Results (Chromic Acid Oxidation) Page 1 of 10

TLC Observations. 3. Create a table in which you insert screenshots of your TLC plates at the beginning (t = 0), midway during the reaction, and after the reaction went to completion. Label each spot on each plate (with compound name or structure). Which compound has the lower R f, the starting material or the product? Explain why this difference in R f makes sense. Jones Oxidation Reaction TLC Plates: Times

TLC Plates

Beginning (t=0)

Starting material (left): benzyl alcohol water chromic/sulfuric acid Starting material (left): benzyl alcohol water chromic/sulfuric acid

Midway

Completion

At the beginning (t=0), there is no difference in Rf because the reaction has not started, so all that was present in the flask was the starting material

Contents at time of reaction (right): benzoic acid chromous sulfate Starting material (left): water Contents at time of reaction (right): benzoic acid chromous sulfate water

Upon completion of the reaction, the product has a lower Rf value than the starting material. This difference makes sense because the starting material is more polar than the product causing the starting material to travel further up the silica gel plate.

Melting Point Analysis. 4. Report the melting point of the product. How can this data be used to help identify the product? The melting point of the product was 122 degrees Celsius. This data can be used to help identify the product by assessing the melting points of other known compounds and finding the one that has the same melting point as the product. Also, the melting point can be used to determine the types of bonds and functional groups present in the product. Page 2 of 10

NMR Analysis. 5. In the table below, draw the structure of benzoic acid, with every H atom drawn out explicitly. The peaks in the NMR spectrum are labeled 1-4. Complete the table below to describe each peak, and number each proton on your drawing to match the corresponding peak in the NMR. 1

H NMR

Peak

Chemical Shift (δ)

Multiplicity†

H‡

d

1H

8.075 1 2 1

2

oh

2

7.95

s

1H

3

7.575

t

2H

4

7.475

t

2H

4

3

3

Benzoic acid label protons) †

Specify the splitting pattern as a singlet (s), doublet (d), triplet (t), quartet (q), or multiplet (m). Specify the number of protons associated with each peak (peak integration, such as 1H, 2H, 3H). ‡

IR Analysis. 6. Insert the image of the IR spectrum of the product in the chromic acid oxidation, and create a table in which you identify the wavenumber (cm -1) for each peak in the diagnostic region, and the bond that it likely corresponds to. Then write 1-2 sentences explaining how this data indicates that the desired product was formed. Page 3 of 10

IR Peak Analysis: Wavenumber (cm-1)

Corresponding Bond

2700-3000

OH from Carboxylic acid (C-O-O-H)

1700

Double bond (C-O)

1450-1600

Aromatic

This data indicates that the desired product was formed because the prominent peaks in the IR spectrum correspond to the structure and bonds of the product. There is a prominent peak around 2700-3000 cm-1 that corresponds to the OH bond from the carboxylic acid in the compound as well as a peak at 1700 cm -1 showing the C-O double bond in the carboxylic acid in the compound. Additionally, the peaks around 1450-1600 cm 1 indicate the presence of an aromatic ring which corresponds to the structure of the product.

Part 3 Results (PCC Oxidation) TLC Observations. 7. Create a table in which you insert screenshots of your TLC plates at the beginning (t = 0), midway during the reaction, and after the reaction went to completion. Label each spot on each plate (with compound name or structure). Which compound has the lower R f, the starting material or the product? Explain why this difference in R f makes sense. Page 4 of 10

PCC Oxidation Reaction TLC Plates: Times Beginning (t=0)

Midway

TLC Starting material (left): benzyl alcohol diethyl ether pyridinium chlorochromate

+

Cl

Starting material (left): benzyl alcohol diethyl ether pyridinium chlorochromate Contents at time of reaction (right): benzaldehyde pyridine

Completio n

Contents at time of reaction (right): diethyl ether benzaldehyde pyridine

Upon completion of the reaction, the starting material has a lower Rf value than the product. This difference makes sense because the product is more polar than the starting material causing the product to travel further up the silica gel plate.

Reaction Work-up. 8. The by-product of the PCC oxidation is pyridine. The pyridine is removed from the organic layer by washing with hydrochloric acid solution. Draw the curved arrows for this proton transfer reaction, and draw the resulting product. Explain how this acid-base extraction effectively removes the pyridine from the organic layer.

NMR Analysis. Page 5 of 10

9. In the table below, draw the structure of benzoic acid, with every H atom drawn out explicitly. The peaks in the NMR spectrum are labeled 1-4. Complete the table below to describe each peak, and number each proton on your drawing to match the corresponding peak in the NMR. 1

H NMR

Multiplicity†

H‡

1

Chemical Shift (δ) 9.9

s

1H

2

7.8

d

2H

3

7.5

d

2H

4

7.4

s

1H

Peak

2 1

2

4

3

3

Benzaldehyde label protons) † ‡

Specify the splitting pattern as a singlet (s), doublet (d), triplet (t), quartet (q), or multiplet (m). Specify the number of protons associated with each peak (peak integration, such as 1H, 2H, 3H)

IR Analysis. 10.Insert the image of the IR spectrum of the product in the PCC oxidation, and create a table in which you identify the wavenumber (cm -1) for each peak in the diagnostic region, and the bond that it likely corresponds to. Then write 1-2 sentences explaining how this data indicates that the desired product was formed.

Page 6 of 10

Wavenumber (cm-1)

Corresponding Bond

2850

sp2 carbon - hydrogen

1700

Double bond (C-O)

1450-1600

Aromatic

This data indicates that the desired product was formed because the prominent peaks in the IR spectrum correspond to the structure and bonds of the product. There is a prominent peak around 2850 cm-1 that corresponds to the sp2 hybridized C-H bond from the carboxyl group in the compound as well as a peak at 1700 cm -1 showing the C-O double bond in the carboxyl group in the compound. Additionally, the peaks around 1450-1600 cm 1 indicate the presence of an aromatic ring which corresponds to the structure of the product.

Reduction of 2-methylcyclohexanone (Experiment 1C):

11. Assuming that 2-methylcyclohexanone was your limiting reagent, calculate the theoretical yield of 2-methylcyclohexanol (in grams) based on the amount of 2-methylcyclohexanone that you used in your reaction. Show all necessary calculations, and use appropriate units, significant figures, etc. Page 7 of 10

The theoretical yield of 2-methylcyclohexanol is 0.611 grams. mol 1 mol 2−methylhexanol =0.00535 mol product × 112.17 g 1 mol 2−methylcyclohexanone 114.19 g 0.00535 mol × =0.611 g 2−methylcyclohexanol 1 mol 2−methylcyclohexanol 0.600 g ×

12.What was the overall percent yield of 2-methylcyclohexanol you obtained? Show all necessary calculations, and use appropriate units, significant figures, etc.

%yield=

0.312 g ×100=51 % 0.611 g

13.Zoom into your product’s NMR spectrum such that you can clearly see the integrated peaks for the geminal proton to the alcohol for the cis and trans products. Insert that figure below.

14.Convert the relative integration ratio of the cis and trans products to a relative percentage. Show all necessary calculations, and use appropriate units, significant figures, etc. 1 ×100 %=40 % cis (1+1.5) 1.5 ×100 %=6 0 % trans (1+1.5) Page 8 of 10

15.Using the overall percent yield and relative percentage of cis product calculated above, determine the percent yield of the cis product. Then do the same for the trans product. Show your calculations. 100 x=40 × 51 2,040 x= =20.40 % 100

16.Insert a figure of your IR spectrum. According to your IR spectrum, was there any starting material remaining at the end of your reaction? Be specific about what data in the IR spectrum gives you this information.

Transmission (%)

2-methylcyclohexanol

3550

3050

2550

2050

1550

1050

100 90 80 70 60 50 40 30 20 10 0 550

Wavenumber (1/cm)

The IR spectrum indicates that there was some starting material remaining at the end of the reaction. This is shown through the small rapid instance of signals occurring around the wavenumbers 1950-2350. These signals are too small to determine what caused them which can be an indication of an impurity.

17.Why do we not use 1H NMR to give us this information? The 1H NMR spectrum of 2methylcyclohexanone is in Figure 1.

Page 9 of 10

Figure 1. The 1H NMR spectrum of 2-methylcyclohexanone.

We do not use 1H NMR to give us this information because there are not enough clear and distinct peaks that can be analyzed and used to determine the structure or identity of the product.

18.Write an abstract in 100 words or less that succinctly describes 1. The reaction performed, 2. The techniques used, and 3. The major conclusions drawn. It should be written in thirdperson, passive voice in the past-tense. For formatting help, see the Scientific Writing section in the Guidelines for Writing Lab Reports in Organic Chemistry handout on Blackboard. In this experiment, a reduction reaction of 2-methylcyclohexanone was performed using sodium borohydride (NaBH4) in order to determine the relative ratios of its two diastereomer products, cis and trans 2-methylcyclohexanol. Extraction was used and repeated in this experiment in order to isolate the desired product from the byproducts and excess reagents. The product was then placed in the rotary evaporator to remove any excess water. The product residue left over from the rotary evaporator was then used to conduct a 1H NMR and IR analysis. Based on the analyses conducted, it was concluded that the desired product was achieved through the experiment. The relative integration ratios of the cis and trans product were 40% cis and 60% trans.

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