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17.E: Carbonyl Compounds II (Exercises)

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    83571
  • Exercise 17-1 Other groups in addition to carbonyl groups enhance the acidities of adjacent \(\ce{C-H}\) bonds. For instance, nitromethane, \(\ce{CH_3NO_2}\), has p\(K_a = 10\); ethanenitrile, \(\ce{CH_3CN}\), has a p\(K_a \cong 25\). Explain why these compounds behave as weak acids. Why is \(\ce{CH_3COCH_3}\) a stronger acid than \(\ce{CH_3CO_2CH_3}\)?

    Exercise 17-2 Draw valence-bond structures to represent the anions derived from the following compounds in the presence of a strong base. Assume that the base functions to remove the most acidic proton.

    a. \(\ce{CH_3COCH_2CO_2CH_3}\)
    b. \(\ce{CH_3COCH_2CN}\)
    c.
    d.* \(\ce{CH_3COCH_2} \overset{\oplus}{\ce{S}} \ce{(CH_3)_2}\)

    Exercise 17-3 Explain why the \(D\) or \(L\) enantiomer of a chiral ketone such as 4-phenyl-3-methyl-2-butanone racemizes in the presence of dilute acid or dilute base.

    Exercise 17-4

    a. The proton NMR spectrum of 2,4-pentanedione is shown in Figure 17-1. Interpret this spectrum by assigning each resonance to a structurally different proton, and explain why the broad resonance at \(15 \: \text{ppm}\) is at unusually low field strengths.

    b. What does this spectrum indicate about the rates of the establishment of each of the following equilibria?

    Give your reasoning (review Sections 9-10E and 9-10C).

    Exercise 17-5

    a. Would you expect the enol or the enolate anion of 2-propanone to be more reactive toward bromine if each were present at the same concentration? Why?

    b. Would you expect the enolate anion to react with bromine at the oxygen? Explain. (Consider the bond energies involved!)

    Exercise 17-6 Would you anticipate any significant difference in the rate of halogenation between \(\ce{CH_3COCH_3}\) and \(\ce{CD_3COCD_3}\) under (a) basic conditions and (b) acidic conditions? Explain. (Review Section 15-6B.)

    Exercise 17-7 A detailed study of the rate of bromination of 2-propanone in water, in the presence of ethanoic acid and ethanoate ions, has shown that \(v = \left\{ 6 \times 10^{-9} + 5.6 \times 10^{-4} \left[ \ce{H_3O^+} \right] + 1.3 \times 10^{-7} \left[ \ce{CH_3CO_2H} \right] + 7 \left[ \ce{OH^-} \right] + 3.3 \times 10^{-6} \left[ \ce{CH_3CO_2^-} \right] + 3.5 \times 10^{-6} \left[ \ce{CH_3CO_2H} \right] \left[ \ce{CH_3CO_2^-} \right] \right\} \left[ \ce{CH_3COCH_3} \right]\) in which the rate \(v\) is expressed in \(\text{mol L}^{-1} \: \text{sec}^{-1}\) when the concentrations are in \(\text{mol L}^{-1}\).

    a. Calculate the rate of the reaction for a \(1 \: \text{M}\) solution of 2-propanone in water at pH 7 in the absence of \(\ce{CH_3CO_2H}\) and \(\ce{CH_3CO_2^-}\).

    b. Calculate the rate of the reaction for \(1 \: \text{M}\) 2-propanone in a solution made by neutralizing \(1 \: \text{M}\) ethanoic acid with sufficient sodium hydroxide to give pH 5.0 (\(K_a\) of ethanoic acid \(= 1.75 \times 10^{-5}\)).

    c. Explain how the numerical values of the coefficients for the rate equation may be obtained from observations of the reaction at various pH values and ethanoate ion concentrations.

    d. The equilibrium concentration of enol in 2-propanone is estimated to be \(\sim 1.5 \times 10^{-4} \%\). If the rate of conversion of \(1 \: \text{M}\) 2-propanone to enol at pH 7 (no \(\ce{CH_3CO_2H}\) or \(\ce{CH_3CO_2^-}\) present) is as calculated in Part a, calculate the rate of the reverse reaction from enol to ketone at pH 7 if the enol were present in \(1 \: \text{M}\) concentration.

    e. Suggest a mechanistic explanation for the term \(3.5 \times 10^{-6} \left[ \ce{CH_3CO_2H} \right] \left[ \ce{CH_3CO_2^-} \right]\) in the rate expression.

    Exercise 17-8 In which of the ketones studied in Section 17-1 would you expect the rate-limiting step in halogenation to be the reaction of the enol with halogen rather than formation of the enol?

    Exercise 17-9

    a. Explain why 2-butanone is halogenated preferentially on the ethyl side with an acidic catalyst. (Review of Section 11-3 should be helpful.)

    b. What product would predominate in the acid-catalyzed bromination of 1-phenyl-2-propanone? Give your reasoning.

    Exercise 17-10 When a small amount of bromine is added to a solution of cyclohexanone in carbon tetrachloride, the brown-red bromine color persists for quite some time. Subsequent additions of bromine result in more rapid reaction and finally the bromine is decolorized almost as rapidly as it can be poured in (until all of the ketone has reacted). Explain this sequence of events.

    Exercise 17-11 The direct halogenation of aldehydes under either acidic or basic conditions is complicated by side reactions involving either oxidation of the aldehyde \(\ce{-CHO}\) group or additions to the \(\ce{-CH=O}\) double bond. Therefore the synthesis of \(\alpha\)-halo aldehydes by the procedure described for ketones is not of much practical value. The enol ethanoate is made by treating the aldehyde with ethanoic anhydride and potassium ethanoate. The overall sequence follows:

    Write the structures of the intermediate products, B and C, and the steps involved in each of the reactions to produce A, B, C, and 2-bromopropanal. What is the function of potassium ethanoate in the formation of A? (You may wish to review Sections 15-4D and 15-4E.)

    Exercise 17-12 Trichloromethane (chloroform) at one time was synthesized commercially by the action of sodium hypochlorite on ethanol. Formulate the reactions that may reasonably be involved. What other types of alcohols may be expected to give haloforms with halogens and base?

    Exercise 17-13 The \(\Delta H^0\) values calculated from bond energies for the following reactions in the vapor phase are equal \(\left( \sim 9 \: \text{kcal mol}^{-1} \right)\):

    Explain why the first, but not the second, reaction proceeds rapidly with the aid of sodium hydroxide. Would you expect ethanoic acid to undergo the haloform reaction? Explain.

    Exercise 17-14* The Haller-Bauer cleavage of 2,2-dimethyl-1-phenyl-1-propanone with sodium amide forms benzenecarboxamide and 2-methylpropane. Write a mechanism for the Haller-Bauer reaction analogous to the haloform cleavage reaction.

    Exercise 17-15* When 2-chlorocyclohexanone-2-\(\ce{^{14}C}\) was treated with sodium methoxide, the \(\ce{^{14}C}\) label in the methyl cyclopentanecarboxylate formed was found at the 1-position \(\left( 50\% \right)\) and 2,5-positions \(\left( 50\% \right)\) of the ring:

    In the related reaction of the chiral chloroketone \(5\), which has the configuration shown, the product is the cyclohexanecarboxylic acid, \(6\), with the configuration as shown:

    These facts have been interpreted as indicating a mechanism involving the following intermediates (where \(^\ominus \ce{OCH_3}\) is used as the base):

    Show in detail how the given results are in accord with this mechanism and how they rule out the following alternative scheme:

    Exercise 17-16 When the aldol reaction of ethanal is carried on in \(\ce{D_2O}\) containing \(\ce{OD}^\ominus\), using moderate concentrations of undeuterated ethanal, the product formed in the early stages of the reaction contains no deuterium bound to carbon. Assuming the mechanism discussed in this section to be correct, what can you conclude as to which step in the reaction is the slow step? What then would be the kinetic equation for the reaction? What would you expect to happen to the kinetics and the nature of the product formed in \(\ce{D_2O}\) at very low concentrations of ethanal?

    Exercise 17-17 What would be the products expected from aldol additions involving propanal, 2,2-dimethylpropanal, and a mixture of the two aldehydes?

    Exercise 17-18 At what point would the system shown in Figure 17-2 cease to produce more \(11\)? What would happen if some barium hydroxide were to get through a hole in the thimble and pass into the boiler? Why is barium hydroxide more suitable for this preparation than sodium hydroxide?

    Exercise 17-19 To obtain high yields of the mono adduct 4-hydroxy-2-butanone, from aldol addition of 2-propanone to methanal, it usually is necessary to use an apparatus such as that shown in Figure 17-3. The 2-propanone is placed in the round-bottom flask with a weak nonvolatile acid, such as butanedioic (succinic) acid, \(\ce{(CH_2CO_2H)_2}\). The 2-propanone is heated in the flask and the vapors are condensed and returned to the flask through the column that is packed with glass beads. When a good flow of 2-propanone is attained through the column, a basic solution of methanal is slowly dripped in. Explain how this arrangement ensures a high conversion to the monohydroxymethyl derivative, \(\ce{HOCH_2CH_2COCH_3}\), with a minimum of reversion to 2-propanone and methanal. Why is \(\ce{(CH_3)_2C(OH)CH_2COCH_3}\) (\(11\)) not formed in significant amounts?

    Figure 17-3: Apparatus for the preparation of monohydroxymethane aldol-addition products from methanal and carbonyl compounds with more than one \(\alpha\) hydrogen.

    Exercise 17-20 Predict the principal products to be expected in each of the following reactions; give your reasoning:

    a. \(\ce{CH_3CHO} + \ce{(CH_3)_2CO} \overset{\ce{NaOH}}{\longrightarrow}\)

    b. \(\ce{(CH_3)_2C(OH)CH_COCH_3} \overset{\ce{NaOH}}{\longrightarrow}\)

    c. \(\ce{CH_2O} + \ce{(CH_3)_3CCHO} \overset{\ce{NaOH}}{\longrightarrow}\)

    d. \(\ce{CH_2O} + \ce{(CH_3)_2CHCHO} \overset{\ce{Ca(OH)_2}}{\longrightarrow}\)

    Exercise 17-21

    a. A useful modification of aldol addition to methanal, known as the Mannich reaction, uses a secondary amine (usually as its hydrochloride salt) to selectively introduce one carbon atom at the alpha position of an aldehyde or ketone. The actual product is the salt of an amino ketone. For example,

    \[\ce{C_6H_5COCH_3} + \ce{CH_2O} + \ce{(CH_3)_2} \overset{\oplus}{\ce{N}} \ce{H_2} \overset{\ominus}{\ce{Cl}} \underset{\text{(solvent)}}{\overset{\ce{C_2H_5OH}}{\longrightarrow}} \ce{C_6H_5COCH_2CH_2} \overset{\oplus}{\ce{N}} \ce{H(CH_3)_2} \overset{\ominus}{\ce{Cl}}\]

    Write the steps involved in this reaction, assuming that an intermediate imminium ion, \(\ce{(CH_3)_2} \overset{\oplus}{\ce{N}} \ce{=CH_2}\), is formed from the amine and methanal.

    b. Show how the reaction product - the so-called Mannich base - could be converted to \(\ce{C_6H_5COCH=CH_2}\).

    Exercise 17-22 Explain why many \(\beta\)-halo ketones undergo \(E2\) elimination with considerable ease. What kinds of \(\beta\)-halo ketones do not undergo such elimination readily?

    Exercise 17-23 Aldol additions also occur in the presence of acidic catalysts. For example, 2-propanone with dry hydrogen chloride slowly yields \(\ce{(CH_3)_2C=CHCOCH_3}\) (mesityl oxide) and \(\ce{(CH_3)_2C=CHCOCH=C(CH_3)_2}\) (phorone). Write mechanisms for the formation of these products, giving particular attention to the way in which the new carbon-carbon bonds are formed.

    Exercise 17-24 What features of the base-catalyzed dehydration of 3-hydroxybutanal make it a more favorable and faster reaction than would be expected for a base-catalyzed dehydration of 2-butanol? Give your reasoning.

    Exercise 17-25 Show how the following compounds can be synthesized from the indicated starting materials by a route having as at least one step an aldol addition:

    a. from ethanal

    b. \(\ce{CH_3CH=CH-CH_2OH}\) from ethanal

    c. \(\ce{(CH_3)_2CHCH_2CH_2CH_3}\) from 2-propanone

    d. from propanal

    e. \(\ce{C_6H_5CH_2CH_2CH_2CH_2CHO}\) from benzenecarbaldehyde and ethanal

    Exercise 17-26 Devise a reasonable synthesis of each of the following compounds from the indicated starting materials. Assume that other needed reagents are available. (Not all of the syntheses involve aldol-addition reactions, but all involve at some stage or the other carbonyl-addition reactions.)

    a. propenenitrile from ethanal
    b. 1-(trichloromethyl)cyclohexanol from cyclohexanone
    c. 2,2-dimethyl-1,3-propanediol from 2-methylpropanal
    d. 2-(phenylmethylidene)cyclohexanone form cyclohexanone
    e. 2,3-diphenylpropenenitrile from phenylethanenitrile
    f. from a compound with only one cyclohexane ring
    g. 3-methyl-2-cyclopentenone from an open-chain compound

    Exercise 17-27 If methyl iodide gives mainly \(\ce{C}\)-alkylation with the enolate anion of 2-propanone, which of the following halides would you expect to be candidates to give \(\ce{O}\)-alkylation: tert-butyl chloride, phenylmethyl chloride, 3-chloropropene, neopentyl chloride?

    Exercise 17-28

    a. Alkylation of ketones is much less successful with ethyl and higher primary halides than for methyl halides. Explain why competing reactions may be particularly important for such cases.

    b. What would you expect to happen if you were to try to alkylate ethanal with \(\ce{KNH_2}\) and \(\ce{CH_3I}\)?

    Exercise 17-29 If you wished to prepare the methyl ether of 4-hydroxy-3-penten-2-one by \(\ce{O}\)-alkylation, what base and which fo the methylating agents listed would you choose? \(\ce{CH_3Cl}\), \(\ce{CH_3I}\), \(\ce{CH_3OCO_2OCH_3}\), \(\ce{(CH_3)_3} \overset{\oplus}{\ce{O}} \overset{\ominus}{\ce{BF_4}}\), or \(\ce{(CH_3)_2O}\). Give your reasoning.

    Exercise 17-30 Show the steps that are likely to take place in the following transformations:

    a.

    b.

    (Review Section 14-6.)

    Exercise 17-31 Show how the following transformations can be carried out. Indicate the conditions, particularly the bases used, necessary reagents, and any expected byproducts.

    a.

    b.

    c.

    Exercise 17-32* The immonium ion formed on \(\ce{C}\)-alkylation of an enamine is easily hydrolyzed to a ketone. Write the steps involved and show how this reaction differs from the acid-catalyzed formation of enamines discussed in Section 16-4C.

    Exercise 17-33* Show how the following transformation could be achieved by way of an enamine:

    Indicate what other alkylation products may be formed and explain why the one shown is the actual product.

    Exercise 17-34* Show the products formed in each step of the following reactions:

    a. \(\ce{CH_3SOCH_2SCH_3} \overset{\ce{NaH}}{\longrightarrow} \: \overset{\ce{CH_3(CH_2)_5Br}}{\longrightarrow} \: \underset{\ce{HCl}}{\overset{\ce{H_2O}}{\longrightarrow}}\)

    b. \(\ce{(CH_3)_2CHCHO} + \ce{HS(CH_2)_3SH} \overset{\ce{HCl}}{\longrightarrow} \: \overset{\ce{CH_3(CH_2)_3Li}}{\longrightarrow} \: \overset{\ce{CH_3(CH_2)_4I}}{\longrightarrow} \: \underset{\ce{Ni}, \: \text{(Raney)}}{\overset{\ce{H_2}}{\longrightarrow}}\)

    c.

    Exercise 17-35 Interpret the proton NMR spectra given in Figure 17-4 in terms of structures of compounds with the molecular formulas \(\ce{C_6H_{10}O}\) and \(\ce{C_9H_8O}\). The latter substance has a phenyl \(\left( \ce{C_6H_5} \right)\) group. Show how each compound may be synthesized from substances with fewer carbons.

    Figure 17-4: Proton NMR spectra at \(60 \: \text{MHz}\) with tetramethylsilane as standard. See Exercise 17-35.

    Exercise 17-36

    a. Explain why the addition of \(\ce{HCl}\) to propenal gives a different orientation than in the addition of \(\ce{HCl}\) to 1,3-butadiene. (Review Section 13-2.)

    b. What products would you expect from the addition of bromine to 3-buten-2-one? Would you expect this addition to be more, or less, rapid than the addition of bromine to 1-butene? Why?

    Exercise 17-37 On what basis can you account for the fact that \(\ce{HCN}\) adds to the carbonyl group of 3-butenal and to the double bond of 3-buten-2-one? Would you expect the carbonyl or the double-bond addition product of \(\ce{HCN}\) to 3-buten-2-one to be more thermodynamically favorable? Give your reasoning.

    Exercise 17-38 Write reasonable mechanisms for the reaction of ketene with alcohols and amines. Would you expect these reactions to be facilitated by acids, or by bases?

    Exercise 17-39 Write a mechanism for the acid-catalyzed reaction of methanol with diketene that accords with the nature of the reagents involved.

    Exercise 17-40 The following structures have been proposed, or could be proposed, for diketene. Show how infrared, Raman, ultraviolet, and NMR spectroscopy may be used to distinguish between the possibilities (if necessary review Chapter 9).

    Exercise 17-41 1-Propen-1-one (methylketene) forms a dimer, \(\ce{C_6H_8O_2}\), by [2 + 2] cycloaddition with itself. The NMR spectrum of the dimer is shown in Figure 17-5. Assign a structure to the dimer consistent with the spectrum.

    Figure 17-5: Proton NMR spectrum at \(60 \: \text{MHz}\) with tetramethylsilane as standard.

    Exercise 17-42 What experiments may be done to prove or disprove the following mechanism for rearrangement of ethanedial to hydroxyethanoic acid?

    Exercise 17-43 Write a mechanism analogous to that for the Cannizzaro reaction for the benzilic acid transformation. What product would you expect to be formed from diphenylethanedione with potassium tert-butoxide in tert-butyl alcohol? Would you expect a benzilic acid-type rearrangement to occur with 2,3-butanedione? Give your reasoning.

    Exercise 17-44 1,2-Cyclopentanedione exists substantially is the monoenol, whereas 2,3-butanedione exists as the diketo form. Suggest explanations for this behavior that take into account possible conformational differences between the two substances. How easily would you expect dione \(15\) to enolize? Why?

    Exercise 17-45 2,6-Bicyclo[2.2.2]octanedione, \(16\), exhibits no enolic properties. Explain.

    Exercise 17-46* If the keto form of 2,4-pentanedione is more stable than the enol form in water solution, why does it also have to be a weaker acid than the enol form in water solution?

    Exercise 17-47 Interpret the proton NMR spectrum shown in Figure 17-6 in terms of possible structures of compounds with molecular formula \(\ce{C_{10}H_{10}O_2}\) with one phenyl group, \(\ce{C_6H_5}-\).

    Figure 17-6: Proton NMR spectrum of \(\ce{C_{10}H_{10}O_2}\) at \(60 \: \text{MHz}\) with tetramethylsilane as the standard. The integral of the offset peak at \(16.1 \: \text{ppm}\) has the same vertical scale as the other integral lines. See Exercise 17-47.

    Exercise 17-48 Write a reasonable mechanism, supported by analogy, for the acid-catalyzed dehydration of 2,5-hexanedione to 2,5-dimethyloxacyclopenta-2,4-diene, \(17\).

    Exercise 17-49* Devise a synthesis of diphenylpropanetrione from 1,3-diphenyl-1,3-propanedione, \(\ce{(C_6H_5CO)_2CH_2}\). How could you determine whether the center or one of the flanking carbonyl groups is lost, as carbon monoxide, with aluminum chloride?

    Exercise 17-50* What properties would you expect for 1,3,5-cyclohexanetrione?

    Exercise 17-51 It is just as important to be able to recognize reactions which do not work as it is to recognize reactions that do work. The following equations represent "possible" synthetic reactions. Consider each carefully and decide whether it will proceed as written. Show your reasoning. If you think a different reaction will take place, write an equation for it.

    a. \(\ce{CH_3COCH_3} + 6 \ce{Br_2} + 8 \ce{NaOH} \rightarrow 2 \ce{CHBr_3} + \ce{Na_2CO_3} + 6 \ce{NaBr} + 6 \ce{H_2O}\)
    b. \(\ce{CH_3CHO} + \ce{NaNH_2} + \ce{(CH_3)_3CCl} \rightarrow \ce{(CH_3)_3CCH_2CHO} + \ce{NH_3} + \ce{NaCl}\)
    c. \(\ce{(CH_3)_2CHCOCH_3} + \ce{CH_2=O} \overset{\ce{Ca(OH)_2}}{\longrightarrow} \ce{(CH_3)_2C(CH_2OH)COCH_3}\)
    d. \(\ce{CH_3CHO} + \ce{CH_3CO_2C_2H_5} \overset{\ce{OH}^\ominus}{\longrightarrow} \ce{CH_3CH(OH)CH_2CO_2C_2H_5}\)
    e. \(\ce{CH_3COCH_2COCH_3} + \ce{CH_2=C=O} \rightarrow \ce{CH_3COOC(CH_3)=CHCOCH_3}\)

    Exercise 17-52 Write equations for a practical laboratory synthesis of each of the following substances from the indicated starting materials (several steps may be required). Give reagents and conditions.

    a. from
    b. \(\ce{CH_2=CHCOCH_3}\) grom \(\ce{CH_3COCH_3}\)
    c. \(\ce{(CH_3)_3CCO_2H}\) from \(\ce{(CH_3)_2C(OH)C(CH_3)_2OH}\)
    d. \(\ce{(CH_3)_3CCOC(CH_3)_3}\) from \(\ce{CH_3CH_2COCH_2CH_3}\)
    e. from \(\ce{(CH_3CH_2)_2CHCOBr}\)
    f. \(\ce{(CH_3)_2CHCH_2COCH_2Br}\) from \(\ce{CH_3COCH_3}\)
    g. \(\ce{CH_3CH_2CH(OH)CN}\) from \(\ce{CH_3CHO}\)
    h. \(\ce{(CH_3)_2CHCH_2CH(CH_3)_2}\)
    i. \(\ce{CH_3CH_2CH(CH_3)CHO}\) from \(\ce{CH_3CH_2CH_2CHO}\)
    j. \(\ce{CH_3C(CH_2OCOCH_3)_3}\) from \(\ce{CH_3CH_2CHO}\)
    k. \(\ce{(CH_3)_3CCH_2CH_2CH_3}\) from \(\ce{(CH_3)_3CCOCH_3}\)

    Exercise 17-53 For each of the following pairs of compounds show explicitly how a chemical test, preferably a test-tube reaction, can be used to distinguish between the two compounds. Describe the observation by which the distinction is made.

    a. \(\ce{CH_3COCH_2CH_2COCH_3}\) and \(\ce{CH_3COCH_2COCH_3}\)
    b. \(\ce{(CH_3CH_2CH_2CH_2)_2CO}\) and \(\ce{[(CH_3)_3C]_2CO}\)
    c. \(\ce{(CH_3)_2C(OH)CH_2COCH_3}\) and \(\ce{(CH_3)_2CHCH(OH)COCH_3}\)
    d. \(\ce{C_6H_5COCOC_6H_5}\) and \(\ce{C_6H_5COCH_2COC_6H_5}\)
    e. and \(\ce{CH_3COCH=C=O}\)
    f. \(\ce{CH_3CH=C=O}\) and \(\ce{CH_2=CH-CH=O}\)
    g. and
    h. \(\ce{ClCH_2CH_2COCH_3}\) and \(\ce{CH_3CH(Cl)COCH_3}\)

    Exercise 17-54 How may spectroscopic means be used to distinguish between the pairs of compounds in Exercise 17-53?

    Exercise 17-55 How may spectroscopic methods be used to distinguish between the isomeric compounds in the following pairs:

    a. \(\ce{CH_3CH=CHCOCH_3}\) and \(\ce{CH_2=CHCH_2COCH_3}\)
    b. \(\ce{CH_3CH_2CO_2H}\) and \(\ce{CH_3COCH_2OH}\)
    c. and
    d. \(\ce{C_6H_5COCH_2COC_6H_5}\) and 4-\(\ce{CH_3C_6H_4COCOC_6H_5}\)
    e. \(\ce{CH_3CH=C=O}\) and \(\ce{(CH_3)_2C=O}\)
    f.
    g. \(\ce{CH_3COCH(CH_3)COCH_3}\) and \(\ce{CH_3COCH=C(OCH_3)CH_3}\)

    Exercise 17-56

    a. Calculate the percentage of enol present in 1-phenyl-1,3-butanedione from its proton NMR spectrum (Figure 17-6).

    b. Estimate the amount of enol expected to be present at equilibrium as either small, medium, or large for each of the following compounds. Give your reasoning.

    1. \(\ce{C_6H_5COCH_2C_6H_5}\)

    2. \(\ce{CH_3COC(CH_3)_2COCH_3}\)

    3.

    4.

    Exercise 17-57 Write the steps involved, showing probable mechanisms, for each of the following reactions:

    a. \(\ce{(C_6H_5)_2CHCHO} + \ce{CH_2=O} \overset{\ce{K_2CO_3}}{\longrightarrow} \ce{(C_6H_5)_2C(CH_2OH)_2}\)

    b.

    c. \(\ce{C_6H_5COCH(CN)_2} + \ce{CH_2N_2} \overset{\text{ether}}{\longrightarrow} \ce{C_6H_5C(OCH_3)=C(CN)_2}\)

    d. \(\ce{(C_6H_5)_2C=C=O} \underset{2. \: \ce{H_2O}}{\overset{1. \: \ce{LiAlH_4}}{\longrightarrow}} \ce{(C_6H_5)_2CHCHO}\)

    e.

    f.

    g.

    h.

    Exercise 17-58 Explain why oxidation of compound A leads to the \(\alpha\),\(\beta\)-unsaturated ketone B.

    Exercise 17-59 The proton NMR spectra of two compounds of formulas \(\ce{C_4H_7OCl}\) and \(\ce{C_4H_7OBr}\) are shown in Figure 17-7. Assign to each compound a structure that is consistent with its spectrum. Show your reasoning. Give a concise description of the chemical properties to be expected for each compound.

    Figure 17-7: Proton NMR spectra at \(60 \: \text{MHz}\) with TMS as standard. See Exercise 17-59.

    Exercise 17-60 Explain why \(\beta\),\(\gamma\)-unsaturated aldehydes and ketones usually are relatively difficult to synthesize and are found to rearrange readily to the \(\alpha\),\(\beta\)-unsaturated isomers, particularly in the presence of basic reagents:

    \[\ce{CH_2=CH-CH_2-CHO} \overset{\text{base}}{\longrightarrow} \ce{CH_3-CH=CH-CHO}\]

    Exercise 17-61 Devise a synthesis of each of the following compounds using as a key step an aldol-type addition reaction:

    a. \(\ce{C_6H_5CH=CHCOC_6H_5}\)
    b. \(\ce{C_6H_5CH=CHCOCH=CHC_6H_5}\)
    c. \(\ce{C_6H_5CH=C(COCH_3)_2}\)
    d.

    e.* from

    Exercise 17-62 Alkenyl ethers (enol ethers) of the type \(\ce{ROCH=CH_2}\) are more stable to rearrangement to \(\ce{O=CH-CH_2R}\) than is an enol such as \(\ce{HOCH=CH_2}\) to \(\ce{O=CH-CH_3}\). Why? What conditions would you expect to be favorable for rearrangement of an alkenyl ether?

    Exercise 17-63 How would you expect the proton NMR spectrum of cyclopropanone in the cyclic ketone and dipolar ion structures (Section 17-11) to differ? Show your reasoning.

    Exercise 17-64* Calculate \(\Delta H^0\) from bond energies (Table 4-3) for \(\ce{C}\)- and \(\ce{O}\)-alkylation of 2-propanone with \(\ce{CH_3I}\) in accord with the following equations:

    Compare your answers with the \(\Delta H^0\) values calculated for \(\ce{O}\)- and \(\ce{C}\)-addition in the aldol reaction (Section 17-3B).

    How can it be that both \(\ce{C}\)- and \(\ce{O}\)-alkylation of the anion

    with \(\ce{CH_3I}\) have \(\Delta H < 0\)? (Notice that the p\(K_a\) of 2-propanone is about 20 and that of \(\ce{HI}\) is about -9.)

    Contributors

    • John D. Robert and Marjorie C. Caserio (1977) Basic Principles of Organic Chemistry, second edition. W. A. Benjamin, Inc. , Menlo Park, CA. ISBN 0-8053-8329-8. This content is copyrighted under the following conditions, "You are granted permission for individual, educational, research and non-commercial reproduction, distribution, display and performance of this work in any format."