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Problems from Organic Chem Lab

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Please note: questions that require the textbook are not included in this response.

1. If 3-bromo-1-propanol is treated with NaOH, a compound of molecular formula C3H6O is formed. Suggest a structure for this product.
2. What product(s) would you expect to form when tetrahydrofuran is treated with excess hydroiodic acid (HI)?
3. Write a suitable mechanism for the cleavage of butyl isopropyl ether with HI at 100 degrees C to form exclusively isopropyl alcohol and 1-iodobutane. Explain why butyl alcohol and isopropyl iodide are not formed in the reaction.
4. There are only four lines in the aromatic region of the fully 1H decoupled 13C NMR spectrum of propyl p-tolyl ether (110-160 ppm), yet there are six aromatic carbon atoms. Explain.
5. Which is a stronger base; aniline or cyclohexylamine? Explain.
6. Phthalimide has a Ka indicated in your lab textbook on pg. 352 (#6.159). Write an equation for the reaction of phthalimide with potassium amide (a strong base) in N,N-dimethyl formamide (DMF) solvent. Name the product.
7. Predict which of the following species is the most acidic. Explain. (See question # 6.160, pg. 352 in your lab textbook.)
- Phthalimide
- Benzamide
8. N-Phenylmaleimide, the product prepared in Experiment #24B, can act as a dienophile in the Diels-Alder reaction (see Experiments #14 and #15).
Draw the structure of the product that would be formed by the treatment of
N-phenylmaleimide with (a) 3-sulfolene under the conditions given in Experiment #14 and (b) furan.
10. What product would you expect to obtain from reaction of one equivalent of propanol with phthalic anhydride?
11. In the experiment, a point is made that the formation of the azo compound is a slow reaction, but that the rate is increased by raising the pH of the solution. Why is this necessary? In other words, how does the pH of the solution affect the reactivity of the N,N-dimethylaniline reagent.
12. In relation to the previous question (#11), diazonium salts couple with phenols in slightly alkaline solution. What effect does the pH of the solution have on the reactivity of the phenol?
13. What is the main structural feature of the azo dyes that causes them to be colored compounds?
14. Methyl Orange is an acid-base indicator. In dilute solution at pH greater than 4.4, it is yellow. (Consult your lab textbook, pg. 363, question # 6.172 for the structure of the compound.)
At pH = 3.2 the solution appears red. Draw a structure of the species that is formed at the lower pH of the acid proton adds to the azo nitrogen atom adjacent to the aromatic ring containing the -SO3 group. Why does the proton add to this particular nitrogen when two other nitrogen atoms are available in the molecule?
15. In the formation of diacetylferrocene, the product is always the one in which each ring is monoacetylated. Why is no diacetylferrocene produced in which both acetyl groups are on the same aromatic ring?
16. Ferrocene cannot be nitrated using the conventional HNO3-H2SO4 mixed acid conditions, even though nitration is an electrophilic aromatic substitution reaction. Explain.
18. Benzene is brominated in the presence of FeBr3 catalyst. (See your lab textbook, pg. 375, question # 6.181.) Suggest an appropriate mechanism for this reaction.
20. In the experiment, sodium bisulfite solution is added at the end in order to destroy the unreacted bromine. What reaction is occurring here? Is HSO3- acting as an oxidizing or reducing agent? Write a balanced equation as part of your answer.:
1. Write equations to show how nitronium ions might be formed using a mixture of nitric and sulfuric acids.
2. Which ring of phenyl benzoate would you expect to undergo nitration more readily? Explain. (Consult your lab textbook pg. 386, question # 6.188.)
3. Give a reasonable explanation of why nitration of 1,4-dichloro-benzene yields the mononitro derivative while N,N'-diacetyl-1,4-phenylenediamine forms the dinitro compound.
4. Explain why p-nitrophenol is a stronger acid than phenol itself. Would pmethoxyphenol be a stronger or weaker acid than phenol? Explain.
8. When 1-octene is treated with NBS, three monobromo straight-chain alkenes having molecular formula C9H17Br are isolated from the reaction mixture. Identify these compounds and give each a suitable name.
9. Benzyl bromide (C6H5CH2Br) can be prepared by treating toluene with NBS in the presence of a peroxide initiator. Suggest a suitable mechanism to account for this reaction.
10. The benzyl radical presented in your lab textbook on pg. 396, question #6.202, has unusual stability. Account for this fact by drawing appropriate resonance structures.
12. 2,3-Dimethyl-2,3-butanediol (pinacol), upon heating in aqueous acid, rearranges to form 3,3-dimethyl-2-butanone (pinacolone). Suggest a mechanism for this reaction.
13. What chemical tests might be used to distinguish between pentanal and 2-pentanone; between benzyl alcohol and diphenylmethanol?
14. Suggest a suitable mechanism for the reaction of 9-fluorenone with 2,4- dinitrophenylhydrazine to form the corresponding 2,4-dinitrophenylhydrazone.
15. There are actually two isomeric 2,4-dinitrophenylhydrazones of 2-pentanone. Draw the structures of these isomers.
16. 2-Pentanone, in reference to the previous question (#15) also forms a derivative on treatment with semicarbazide. (See your lab textbook, pg. 405, question # 6.213.) Note that semicarbazide has two -NH2 groups that might react with the carbonyl of the ketone to form semicarbazone.
Explain why it reacts as depicted in the lab textbook.
17. The haloform reaction using I2 and NaOH is referred to as the "iodoform" test for methyl ketones. The test also gives positive results for compounds containing the -CH(OH)CH3 group. This results from the oxidation of the alcohol to the methyl ketone in the first stage. Write a balanced equation for the conversion of C6H5CHOHCH3 to the methyl ketone in the presence
of I2 and NaOH. Identify which species is being oxidized and which is being reduced.
18. If you were carrying out an industrial scale synthesis in which one step involved a haloform reaction to convert a methyl ketone into the corresponding acid having one less carbon atom, would you use NaOH and Cl2, NaOH and Br2, or NaOH and I2 reagent? Give reasons for your choice.
19. Over the years the two isomers of azobenzene have been designated by various terms: cis-trans, syn-anti, and E-Z. Using each set of terms, assign them to the isomers of azobenzene.
20. Discuss what you would observe after elution and visualization of a TLC plate having made the following mistakes in carrying out the analysis.
a. The solvent level in the developing jar was higher than the original line on which the samples were spotted.
b. Too much sample was applied to the TLC plate.

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Acid and Base Organic Chemistry Example Problems

I have most of the answers on the attachment. I just looking to see if I am on the right track. I have added everything including back ground info that was posted on my lab assignment. I have also included all of my lab work which is completed and assumed correct on an attachment below.

1. What is the equivalence volume of the second titration? That is, how many mL of NaOH were added to the solution to cause the solution to turn pink? Note that you must calculate this volume; it is not the burette reading!

2. What is the pH at the equivalence point?

3. Calculate the molarity of the HCl from the volumes of acid and base at the equivalence point and the molarity of the NaOH. Use the equation given in the Background section.

4. Generate a titration curve by plotting the pH on the y-axis and the number of mL of base added to the flask on the x-axis. How do you determine the equivalence volume of the titration from this curve? What is the equivalence volume according to the titration curve? Calculate the molarity of the acid using this equivalence volume and the equation provided in the Background section of this laboratory. Why use a titration curve when the raw data are available in your data table?

5. How is the number of moles of NaOH affected at the equivalence point of the solution? Explain.

6. Compare the molarity of the acid determined by different individuals in the class. Are all these values same? Why, or why not?

Back Ground and procedures:

Titration is one of the most useful techniques for determining the concentration of an unknown solution, and it is often used with acidic and basic solutions. An apparatus called a burette is used to add very small controlled amounts of substance to a solution to the point at which the characteristics of the solution reach a specific point of change. The end point of titration is reached when a stoichiometric number of moles of an acid or base are added to the unknown solution to neutralize it.

PLEASE NOTE: The technique of titrating an acid with a base involves several steps in order to obtain exact results. Thus it is important to follow precisely the laboratory procedure.

The determination of the end point of titration can be detected by several methods:

- indicator - a substance is added to the solution that changes color when the end point of titration is reached.

- pH meter - a potentiometric change in the solution as indicated by a pH meter as the solution transitions from acidic to basic or vice versa.

- spectrophotometer - a change in the amount of light absorbed by the solution as indicated by a spectrophotometer as the solution transitions in relative concentrations of substances.

- conductivity meter - a change in the conductivity of electricity of the solution as it transitions in relative concentrations of substances.

In this lab an indicator, phenolphthalein, will be used to determine the end point of titration to determine the concentration of a substance in a solution. Phenolphthalein causes the solution color to change from clear to pink at the endpoint of titration.

A graph called a "titration curve" is used to determine the precise endpoint of titration. The titration curve is generated by plotting the the pH of the solution vs. the amount of base (in mL) added to the solution. The number of mL of base added to an acid in order to reach the endpoint or equivalence point is called the equivalence volume.

When titrating a monoprotic acid, such as HCl, with sodium hydroxide (NaOH), the molar ratio for the reaction is 1:1 - that is, one mole of NaOH will neutralize one mole of HCl - and all of the following are true at the equivalence point:

(a) Moles of acid in flask = moles of base added from the buret

(b) (molarity of acid) x (volume of acid) = (molarity of the base) x (volume of added base)

Equation (b) takes the familiar form M1*V1 = M2*V2, from which the molarity of the acid, M2, is determined.

1. Take a clean Erlenmeyer flask from the Glassware shelf and place it on the workbench.

2. Add 25 mL HCl (of unknown concentration) to the flask.

3. Add 2 drops of phenolphthalein, an indicator, to the flask.

4.Take a burette from the Glassware shelf and place it on the workbench.

5. Fill the burette with 50 mL of 0.5M NaOH solution. Record this initial volume.

6. Drag the flask to the lower half of the burette such that the burette can deliver NaOH to the flask. Make sure the burette and the flask are connected.

7. Open the Data window and click on the flask. Click the pushpin icon in the Data window to lock its display to the flask.

8. Take a pH meter from the Tools shelf and set it on the flask. Record the initial pH of the solution.

9. Open the Properties window and click on the burette. Enter "1" in the amount window to add NaOH to the flask in 1 mL increments. One mL of NaOH will be delivered to the flask each time the stopcock button is clicked.

10. Set up a data table on a piece of paper with the following column headings:
mL of base (burette reading)
pH
moles of NaOH

11. Click the stopcock button on the Properties window to deliver 1 mL of NaOH to the flask. Continue to add NaOH in 1 mL increments. Record the mL of base (burette reading), the pH of the solution in the flask, and the moles of NaOH in the flask for each mL of base added. Note that the initial mL of base is 50 mL, which is equal to zero mL of base added to the flask.

12. The solution in the flask will change in color from clear to pink due to the phenolphthalein indicator when the endpoint is either reached or crossed. Mark the point in the data table at which the color change occurs.

13. Add 5 more 1 mL increments of NaOH to the flask recording the mL of base, the pH, and the moles of NaOH at each increment.

14. Detach the pH meter and drag the burette and flask to the recycling chute.

15. Take a new flask from the Glassware shelf and place it on the workbench.

16. Add 25 mL of HCl and 2 drops of phenolphthalein to the flask.

17. Set a new burette on the workbench and fill it with 50 mL of NaOH.

18. Place the flask under the burette and attach the pH meter.

19. Based on the results of the previous titration, you may initially add a relatively large amount of NaOH solution all at once to the flask to get to 1 mL BEFORE the endpoint. For example, if 20 mL of NaOH caused a color change in your first titration, you know experimentally that you can add 19 mL of NaOH to the second titration without causing a color change. You can enter 19 in the Properties window and click the stopcock button to deliver 19 mL of NaOH to the flask at once.

20. AFTER the initial delivery of NaOH to the flask, change the amount of NaOH to be delivered to 1 in the Properties window. For this titration, use the DROP-WISE button to deliver very small (0.05 mL) of NaOH per click of the drop-wise button. In this way, you are measuring the endpoint of titration more precisely. Record the mL of base (burette reading), the pH, and the moles of NaOH in the flask with each click of the drop-wise button until the endpoint is reached. Mark this endpoint on your data sheet. Add 5 more drop-wise increments of NaOH noting the mL of base, pH, and moles of NaOH.

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