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CHEM 3780 Orgo II, S12, Exp 5 (Lab #5) (SYNT 720: Aldol)

LAB REPORT INSTRUCTIONS

Carefully read these instructions and complete Section I on page 2 before you come to the lab.

Students may work with a lab partner for the in-lab portion.

The lab report is due at the beginning of the next lab session. The report needs to reflect the

student’s own work, no group work for lab report entries.

Print clearly in your lab notebook so that the carbon copies are legible. Label everything with your name, date, and experiment number when you hand in the duplicate pages and the spectra.

O

benzaldehyde

OH

H H

HO

CH3CH3

10% NaOH

EtOH

dibenzalacetone

Required You must have your goggles and wear appropriate personal protective clothing as discussed in the course syllabus. Carefully read and be familiar with the experimental procedure in the lab manual. Prepare the PreLab and the Introduction of the Lab Report (Section I with bulleted outline) before coming to lab.

Experimental Notes 1. CAUTION: Keep flammable materials away from heat sources. 2. CAUTION: Exercise care when handling corrosive and toxic sodium hydroxide (NaOH). 3. CAUTION: Ensure proper cooling before and during the reaction. 4. CAUTION: Exercise care when handling hot solutions and hot surfaces. 5. CAUTION: Use care when applying vacuum during filtration. 6. You will use the semi-microscale procedure. 7. 8. You will recrystallize your crude product from ethanol (EtOH, CH3CH2OH) as directed in your

laboratory manual. 9. In order to remove residual solvent, you will place the solid product on a piece of filter paper, crush it,

and smear the solid particles back and forth a few times, without scraping off pieces of the paper. Now you can analyze you product.

10. You will analyze your reaction by IR spectroscopy and melting point determination.

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Lab Report Notes

(written in your lab notebook, 50 pts total) Section I Introduction (prepare this section before coming to the lab, 13 pts)

(1 pts) Date and Title of Experiment

(2 pts) Objective (briefly describe in 2 sentences)

(1 pts) Draw the reaction scheme showing the starting material and all possible products.

(2 pts) Compose a table of physical constants for each chemical you use (bp or mp, MW)

(2 pts) List all hazardous compounds

(2 pts) Determine the limiting reagent and calculate the theoretical yield of your product.

(3 pts) Outline the experimental procedure (semi-microscale) by providing a “Bulleted Outline”(in your own words, see posted example online).

Section II Observations and calculations (data recorded during the lab, 7 pts)

1. (4 pts) Note any observations you make during the entire course of the experiment in the bulleted outline.

Carry out the procedure. Recrystallize your product from EtOH. 2. Measure an IR spectrum of your recrystallized product. Proceed to the next step if there is a line at

the instrument room and return to #2 later. Wear gloves when you dissolve 50 mg of your purified product in ca 3 mL of CH2Cl2 (dichloromethane) in the hood. Place 3-4 drops of this solution on the IR plate. Let the solvent evaporate. Then measure the IR spectrum.

3. Obtain a spectrum of benzaldehyde from your TA. 4. (2 pts) Label both spectra with your name, date and lab ID. 5. (1 pts) Obtain and record the melting point of your purified product after recrystallization from

EtOH and “drying” with the filter paper (see Experimental Notes). Section III Results and Discussion (analysis after the experiment is completed, 28 pts)

6. (3 pts) Calculate the percent yield of your purified product. 7. (2 pts) What information from your IR spectrum indicates that dibenzalacetone was formed and

benzaldehyde was completely consumed? 8. (4 pts) Provide a table, as below (for both benzaldehyde and dibenzalacetone), showing the

pertinent IR absorptions and their assignment. 9. (2 pts) What information about the purity of the product could you infer from the melting point? 10. (4 pts) A 1H NMR of starting material and product is attached. Prepare a table similar to the one

shown below in your notebook—for both benzaldehyde and dibenzalacetone.

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11. (4 pts) What is the coupling constant for the olefinic hydrogens? Label the hydrogens on your compound, Ha, Hb, Hc, etc. to correspond with your table assignments.

12. (2 pts) What peaks in the 1H NMR most clearly demonstrate the presence of the desired product? Give the corresponding chemical shifts (ppm) and multiplicity (s, d, t, q, m, etc.)

13. (1 pts) If the product had residual aldehyde, what peak would you expect to observe in the 1H NMR?

14. (4 pts) Propose a mechanism for the base-catalyzed condensation of cyclohexanone with

two molecules of benzaldehyde to give dibanzalcyclohexanone. 15. (2 pts) Dibenzalacetone is commonly used in sunscreens. Suggest what properties are

valuable in a compound for use as sunscreen. You may need to consult reference sources.

1H NMR (compound name) IR (compound name)

Chemical shift (ppm)

# H Coupling constant (if applicable)

Assignment Absorption frequency (cm-1)

Assignment

x.xx # J = z Ha xxxx.xx cm-1 x-y stretch x.yz # J = y Hc yyyy.yy cm-1 y-z stretch

Section IV Conclusions (2 pts)

List two new things you learned in doing this experiment or something that you now understand better than before you did the lab. Explain.

_____________________________ Sign & date your lab report

The lab report is due at the BEGINNING of the next lab session and it needs to reflect the student’s own work, no group work for lab report entries.

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NMR Analysis

1. Identify the olefin hydrogens—they should have identical coupling constants and will integrate to 2 H each since there are two equivalent hydrogens in the symmetrical product.

2. Determine the coupling constant (J) in millimeters (x mm). 3. Determine how many mm are in 1 ppm (y mm). Then,

assume that 1 ppm = 400 Hz = y mm. 4. Set up a ratio and solve for J. This is the coupling constant

between the olefin hydrogens. x mm = _y mm_ J 400 Hz