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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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