carboxylic acid & nitriles

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Homework Ch. 20—Carboxylic Acids and Nitriles-Yellow marked mandatory

SHORT ANSWER

Drawing Instructions: Draw structures corresponding to each of the given names.

1. Draw: 2-propylpentanoic acid

ANS:

2. Draw: cis-1,3-cyclopentanedicarboxylic acid

ANS:

3. Draw: cyanoacetic acid

ANS:

4. Draw: m-chlorobenzoic acid

ANS:

Carboxylic Acids and Nitriles

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5. Draw: 2-propenenitrile

ANS:

IUPAC Naming Instructions: Provide proper IUPAC names.

6. Name:

ANS: 1,5-pentanedioic acid

7. Name:

ANS: o-hydroxybenzoic acid

8. Name:

ANS: 5,5-dimethyl-1,3,6-cycloheptatriene-1-carboxylic acid

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9. Name:

ANS: (R)-3,5-dihydroxy-3-methylpentanoic acid

10. Name:

ANS: (E)-2-methyl-2-butenoic acid

11. Name:

ANS: phenylacetonitrile or 2-phenylethanenitrile

12. What is the correct name for the following structure?

a. 2-oxohexanoic acid b. 5-oxohexanoic acid c. methyl butroxoketone d. 4-ketopentanoic acid

ANS: b


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Exhibit 20-1 Consider the data in the Table below to answer the following question(s):

Acidities of Substituted Benzoic and Acetic Acids pKas at 25°C Y−C6H4COOH

Y Y−CH2COOH meta para H 4.75 4.19 4.19

CN 2.47 3.64 3.55 OCH3 3.57 4.09 4.46

13. Refer to Exhibit 20-1. Draw the structure of the strongest acid in the table above.

ANS: NC−CH2−COOH

14. Refer to Exhibit 20-1. Which of the acids in the table above has the strongest conjugate

base?

ANS: CH3COOH

15. Refer to Exhibit 20-1. Explain why cyanoacetic acid and methoxyacetic acid are more acidic

than their correspondingly substituted benzoic acid counterparts.

ANS: Electron-withdrawing groups, like −CN and −OCH3, inductively withdraw electron density, which stabilizes the resulting carboxylate anion and, thus, increases the acidity of the carboxylic acid. These inductive effects are strongly dependent on distance. The −CN and −OCH3 substituents are closer to the carboxylate in the substituted acetic acids than in the substituted benzoic acids, so their effect is greater.

16. Even through the para position is one carbon farther from the carboxy group than the meta

position, p-cyanobenzoic acid is more acidic than m-cyanobenzoic acid. Explain the differences in acidity between p-cyanobenzoic acid and m-cyanobenzoic acid.

ANS: In p-cyanobenzoic acid, the negative charge of the carboxylate can be better stabilized than in the meta isomer because the electron-withdrawing cyano group polarizes the benzene ring and places a positive charge next to the negatively charged carboxyl group. The same polarization occurs in m-cyanobenzoic acid, but the effect is not as great because the charge is one carbon farther away from the carboxy group.

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17. Explain the differences in acidity between p-methoxybenzoic acid and m-methoxybenzoic

acid.

ANS: p-Methoxybenzoic acid is less acidic than m-methoxybenzoic acid because the carboxyl group is directly conjugated, through the benzene ring, with the electron-donating oxygen lone pairs of the methoxy group. This destabilizes the p-methoxybenzoate anion relative to the m-methoxybenzoate anion by placing two negative charges on the carboxylate group.

Exhibit 20-2 Consider the data below to answer the following question(s). When CO2 is bubbled through an ether solution of benzylmagnesium bromide, and the resulting mixture is acidified, phenylacetic acid is produced. Any unreacted benzylmagnesium bromide is converted to toluene in the acidification step.


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18. Refer to Exhibit 20-2. Write the complete reaction sequence for the process described above.

ANS:

19. Refer to Exhibit 20-2. How could you separate phenylacetic acid from toluene?

ANS: Extract the ether solution containing the mixture of products with a dilute aqueous solution of sodium hydroxide. This converts phenylacetic acid to its carboxylate salt, which will dissolve in the aqueous layer. The toluene will remain in the ether layer. Separate the aqueous and organic layers, acidify the aqueous layer, and extract with an organic solvent to recover the phenylacetic acid.

20. Refer to Exhibit 20-2. This reaction is described as a _____ process. a. carbonylation b. carboxylation c. carbaniolation d. cationation

ANS: b

Exhibit 20-3 What is the order of increasing acidity for the following compounds? (least to most)

21. a. IV, I, III, II b. III, II, I, IV c. II, III, I, IV d. III, II, IV, I

ANS: B

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22.

a. IV, I, III, II b. IV, II, III, I c. II, III, I, IV d. I, III, II, IV

ANS: a

23. a. IV, II, I, III b. I, II, IV, III c. III, I, II, IV d. III, IV, II, I

ANS: c

Exhibit 20-4 Give the major organic product(s) for each of the following reactions or sequences of reactions. Show all relevant stereochemistry.


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24.

ANS:

25.

ANS:

26.

ANS:

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27.

ANS:

28.

ANS:

29.

ANS:

30.

ANS:


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31.

ANS:

32.

ANS:

33.

ANS:

Exhibit 20-5 Choose the best reagent(s) for carrying out the following conversions from the list below. Place the letter corresponding to the best choice in the blank to the left of the conversion. a. KMnO4, H3O+ g. 1. Mg, ether b. CH 3I 2. CO2 c. NaBH4, ethanol 3. H3O+

d. 1. BH3 h. 1. NaCN 2. H3O+ 2. H2SO4, H2, heat e. 1. CH3MgBr, ether i. O3, then Zn and HOAc 2. H3O+ f. CrO3, H2SO4, H2O

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34. _____ CH3CH=CHCH2COOH → CH3COOH + HOOCCH2COOH

ANS: a

35. _____

ANS: g

36. _____

ANS: f

37. _____

ANS: e

Exhibit 20-6 Carboxylic acids are synthesized from alkyl halides via Grignard reagent carboxylation or nitrile hydrolysis. Choose the best method for effecting each of the following conversions. Explain each of your choices. If neither method is appropriate, explain.

38.

ANS: Since SN2 displacements do not occur at tertiary alkyl halides the Grignard reagent carboxylation is the best method for carrying out this conversion.


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39.

ANS: Amine protons interfere with the formation of Grignard reagents, so nitrile hydrolysis is the best method for carrying out this conversion.

40.

ANS: Either method would be appropriate for this conversion.

41.

ANS: Neither method of acid synthesis yields the desired product. Any Grignard reagent formed will react with the carbonyl function group present in the starting material. Reaction with cyanide occurs at the carbonyl functional group as well as at the halogen. However, if the aldehyde is first protected by forming an acetal, either method can be used to synthesize a carboxylic acid.

42. Propose a synthesis of the anti-inflammatory drug Ibuprofen from benzene. Show all

reagents and all intermediate structures. Assume that ortho and para isomers can be separated.

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ANS:

Exhibit 20-7 Show how you would accomplish the following transformations. More than one step may be required. Show all reagents and all intermediate structures.

43.

ANS:

44.


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ANS:

45. Name the following substance. Atoms other than carbon and hydrogen are labeled.

ANS: 4-hydroxy-2,2-dimethylbutanoic acid

46. Name the following substance. Atoms other than carbon and hydrogen are labeled.

ANS: 3-methylbutanenitrile

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47. Draw the structure of the product formed when the following is treated with 1.) NaOH (aq) and 2.) H3O+. Explain, if necessary how the product would be affected if the treatment with acid were omitted.

ANS:

The corresponding conjugate base would be produced.

48. Draw the structure of the reactant needed to form the following upon treatment with SOCl2

at a moderately elevated temperature. Atoms other than carbon and hydrogen are labeled.

ANS:


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MULTIPLE CHOICE

1. Which of the following is not an acyl derivative of a carboxylic acid? a. nitrile c. amide b. ester d. acid chloride

ANS: A

2. Which of the following is not a common feature of both carboxylic acids and nitriles? a. carbon atom with three bonds to an electronegative atom b. presence of π bonds c. can act as electrophiles d. occur frequently in living organisms e. All characterize both functional group classes.

ANS: D

3. A solution of glycolic acid is prepared such that the glycolic acid is 69% dissociated.

Calculate the pH of this solution. ( ) a. 3.83 c. 4.18 b. 6.06 d. 3.48

ANS: C

4. Calculate the percent dissociation of a 0.00100 M solution of lactic acid which has a pH of

4.00. ( ) a. 39% b. 58% c. 42% d. 78% e. Nearly 100%

ANS: B

5. In a solution of acetic acid ( ) at physiological pH of 7.3, it is most accurate

to represent this substance as: a. CH3CO2H b. CH3CO2

– c. CH3CO2H and CH3CO2

–

ANS: B

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6. What reactant could produce the following substance upon treatment with CrO3 under acidic conditions? Atoms other than carbon and hydrogen are labeled.

a. 2, 2-dimethylbutanal b. 2, 2-dimethyl-1-butanol c. 2, 2-dimethylbutanenitrile d. a and b e. a and c f. a, b, and c

ANS: D

7. In order to produce a carboxylic acid as a product of the Grignard reaction, the Grignard

reagent reacts with: a. CO2 b. a methyl ketone c. a methyl ester d. an aldehyde e. either or CO2 a methyl ketone

ANS: A

8. Which labeled peaks in the following spectrum are characteristic of a carboxylic acid?

a. 1 b. 2 c. 3 d. 4 e. 5


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f. 1 and 2 g. 2 and 3 h. All five peaks

ANS: F

9. Which labeled peaks would disappear if D2O were added to the sample?

a. 1 b. 2 c. 3 d. 4 e. All peaks would disappear.

ANS: D

10. The following spectrum is representative which of the following types of compounds?

a. carboxylic acid b. aldehyde c. nitrile d. alcohol e. halide f. Data presented does not provide enough information.

ANS: C

11. A sample is know to contain either hexanoic acid or 3-methylpentanoic acid. Which of the

following spectra would not distinguish between the two isomers? a. 1H NMR b. 13C NMR c. DEPT-90

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d. DEPT-135 e. All would distinguish between the two isomers.

ANS: B

carboxylic acid & nitriles

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