19.19: Additional Problems

Last updated
Save as PDF

Page ID: 459846

$ \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } $

$ \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} $

$ \newcommand{\dsum}{\displaystyle\sum\limits} $

$ \newcommand{\dint}{\displaystyle\int\limits} $

$ \newcommand{\dlim}{\displaystyle\lim\limits} $

$ \newcommand{\id}{\mathrm{id}}$ $ \newcommand{\Span}{\mathrm{span}}$

( \newcommand{\kernel}{\mathrm{null}\,}\) $ \newcommand{\range}{\mathrm{range}\,}$

$ \newcommand{\RealPart}{\mathrm{Re}}$ $ \newcommand{\ImaginaryPart}{\mathrm{Im}}$

$ \newcommand{\Argument}{\mathrm{Arg}}$ $ \newcommand{\norm}[1]{\| #1 \|}$

$ \newcommand{\inner}[2]{\langle #1, #2 \rangle}$

$ \newcommand{\Span}{\mathrm{span}}$

$ \newcommand{\id}{\mathrm{id}}$

$ \newcommand{\Span}{\mathrm{span}}$

$ \newcommand{\kernel}{\mathrm{null}\,}$

$ \newcommand{\range}{\mathrm{range}\,}$

$ \newcommand{\RealPart}{\mathrm{Re}}$

$ \newcommand{\ImaginaryPart}{\mathrm{Im}}$

$ \newcommand{\Argument}{\mathrm{Arg}}$

$ \newcommand{\norm}[1]{\| #1 \|}$

$ \newcommand{\inner}[2]{\langle #1, #2 \rangle}$

$ \newcommand{\Span}{\mathrm{span}}$ $ \newcommand{\AA}{\unicode[.8,0]{x212B}}$

$ \newcommand{\vectorA}[1]{\vec{#1}} % arrow$

$ \newcommand{\vectorAt}[1]{\vec{\text{#1}}} % arrow$

$ \newcommand{\vectorB}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } $

$ \newcommand{\vectorC}[1]{\textbf{#1}} $

$ \newcommand{\vectorD}[1]{\overrightarrow{#1}} $

$ \newcommand{\vectorDt}[1]{\overrightarrow{\text{#1}}} $

$ \newcommand{\vectE}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{\mathbf {#1}}}} $

$ \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } $

$ \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} $

$\newcommand{\avec}{\mathbf a}$ $\newcommand{\bvec}{\mathbf b}$ $\newcommand{\cvec}{\mathbf c}$ $\newcommand{\dvec}{\mathbf d}$ $\newcommand{\dtil}{\widetilde{\mathbf d}}$ $\newcommand{\evec}{\mathbf e}$ $\newcommand{\fvec}{\mathbf f}$ $\newcommand{\nvec}{\mathbf n}$ $\newcommand{\pvec}{\mathbf p}$ $\newcommand{\qvec}{\mathbf q}$ $\newcommand{\svec}{\mathbf s}$ $\newcommand{\tvec}{\mathbf t}$ $\newcommand{\uvec}{\mathbf u}$ $\newcommand{\vvec}{\mathbf v}$ $\newcommand{\wvec}{\mathbf w}$ $\newcommand{\xvec}{\mathbf x}$ $\newcommand{\yvec}{\mathbf y}$ $\newcommand{\zvec}{\mathbf z}$ $\newcommand{\rvec}{\mathbf r}$ $\newcommand{\mvec}{\mathbf m}$ $\newcommand{\zerovec}{\mathbf 0}$ $\newcommand{\onevec}{\mathbf 1}$ $\newcommand{\real}{\mathbb R}$ $\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}$ $\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}$ $\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}$ $\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}$ $\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}$ $\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}$ $\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}$ $\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}$ $\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}$ $\newcommand{\laspan}[1]{\text{Span}\{#1\}}$ $\newcommand{\bcal}{\cal B}$ $\newcommand{\ccal}{\cal C}$ $\newcommand{\scal}{\cal S}$ $\newcommand{\wcal}{\cal W}$ $\newcommand{\ecal}{\cal E}$ $\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}$ $\newcommand{\gray}[1]{\color{gray}{#1}}$ $\newcommand{\lgray}[1]{\color{lightgray}{#1}}$ $\newcommand{\rank}{\operatorname{rank}}$ $\newcommand{\row}{\text{Row}}$ $\newcommand{\col}{\text{Col}}$ $\renewcommand{\row}{\text{Row}}$ $\newcommand{\nul}{\text{Nul}}$ $\newcommand{\var}{\text{Var}}$ $\newcommand{\corr}{\text{corr}}$ $\newcommand{\len}[1]{\left|#1\right|}$ $\newcommand{\bbar}{\overline{\bvec}}$ $\newcommand{\bhat}{\widehat{\bvec}}$ $\newcommand{\bperp}{\bvec^\perp}$ $\newcommand{\xhat}{\widehat{\xvec}}$ $\newcommand{\vhat}{\widehat{\vvec}}$ $\newcommand{\uhat}{\widehat{\uvec}}$ $\newcommand{\what}{\widehat{\wvec}}$ $\newcommand{\Sighat}{\widehat{\Sigma}}$ $\newcommand{\lt}{<}$ $\newcommand{\gt}{>}$ $\newcommand{\amp}{&}$ $\definecolor{fillinmathshade}{gray}{0.9}$

19 • Additional Problems

Visualizing Chemistry

PROBLEM 19-27 Each of the following substances can be prepared by a nucleophilic addition reaction between an aldehyde or ketone and a nucleophile. Identify the reactants from which each was prepared. If the substance is an acetal, identify the carbonyl compound and the alcohol; if it is an imine, identify the carbonyl compound and the amine; and so forth.

(a) (b) A ball-and-stick model shows benzene ring linked to methylene group. This is linked to a nitrogen atom double bonded to carbon. This is linked to two methyl groups.

(c) A ball-and-stick model of a cyclopentene linked to a cyclopentane with nitrogen atom. (d) A ball-and-stick model shows a benzene ring with a methyl group, C H linked to a hydroxyl. C H is also linked to two methyl groups.

PROBLEM 19-28 The following molecular model represents a tetrahedral intermediate resulting from addition of a nucleophile to an aldehyde or ketone. Identify the reactants, and write the structure of the final product when the nucleophilic addition reaction is complete.

PROBLEM 19-29 The enamine prepared from acetone and dimethylamine is shown in its lowest-energy form.

(a) What is the geometry and hybridization of the nitrogen atom?

(b) What orbital on nitrogen holds the lone pair of electrons?

(c) What is the geometric relationship between the p orbitals of the double bond and the nitrogen orbital that holds the lone pair? Why do you think this geometry represents the minimum energy?

the=

Mechanism Problems

PROBLEM 19-30 Predict the product(s) and propose a mechanism for each of the following reactions:

(a) the=

(b) The reaction shows methoxybenzene with acetyl chloride in the presence of aluminum chloride to yield an unknown product denoted by a question mark.

PROBLEM 19-31 Predict the product(s) and propose a mechanism for each of the following reactions:

(a) the=

(b) The reaction shows acetone with (1S,2S)-cyclohexane-1, 2-diol using a hydrogen ion catalyst, yielding an unknown product marked with a question mark.

PROBLEM 19-32 Predict the product(s) and propose a mechanism for each of the following reactions:

(a) The reaction shows fused cyclohexane and cyclopentane rings with oxygen and methyl groups with hydrogen ion catalyst and water to yield an unknown product denoted by a question mark.

(b) The reaction shows a compound with benzene attached to cyclopentane with oxygen, hydrogen, and methyl groups with hydrogen ion catalyst and water, yielding unknown product marked with a question mark.

PROBLEM 19-33 Predict the product(s) and propose a mechanism for each of the following reactions:

(a) The reaction shows pentan-3-one with hydroxylamine to yield an unknown product marked with a question mark.

(b) The reaction shows acetophenone with dimethylamine resulting in an unknown product represented by a question mark.

PROBLEM 19-34 Predict the product(s) and propose mechanisms for the following reactions:

(a) The reaction shows N-(butan-2-ylidine)methanamine with hydrochloric acid and water to yield an unknown product marked with a question mark.

(b) The reaction shows N, N-dimethylcyclohex-1-enamine with hydrochloric acid and water to yield an unknown product marked with a question mark.

PROBLEM 19-35 The following reaction begins with an acetal and converts it into a different acetal. Predict the product(s) and propose a mechanism.

(a) The reaction shows 1,2-dihydroxybenzene and 2, 2-dimethoxypropane in the presence of hydrogen ion to yield the unknown product marked with a question mark.

(b) The reaction shows 3, 3-dimethoxypentane with ethylene glycol in the presence of hydrogen ions, producing an unknown product denoted by a question mark.

PROBLEM 19-36 When α-glucose is treated with an acid catalyst in the presence of an alcohol, an acetal is formed. Propose a mechanism for this process and give the structure of the stereoisomeric acetal that you would also expect as a product.

The reaction shows the conversion of alpha-glucose to acetal in the presence of hydrogen ions and methanol.

PROBLEM 19-37 Predict the products of the following Wolff–Kishner reactions. Write the mechanism for each, beginning from the hydrazone intermediate.

(a) ch 19 p 37a.png (b) ch 19 p 37b.png

PROBLEM 19-38 Aldehydes can be prepared by the Wittig reaction using (methoxymethylene)triphenylphosphorane as the Wittig reagent and then hydrolyzing the product with acid. For example,

ch 19 p 38.png

(a) How would you prepare the necessary phosphorane?

(b) Propose a mechanism for the hydrolysis step.

PROBLEM 19-39 One of the steps in the metabolism of fats is the reaction of an unsaturated acyl CoA with water to give a β-hydroxyacyl CoA. Propose a mechanism.

the=

PROBLEM 19-40 Aldehydes and ketones react with thiols to yield thioacetals just as they react with alcohols to yield acetals. Predict the product of the following reaction, and propose a mechanism:

the=

PROBLEM 19-41 Ketones react with dimethylsulfonium methylide to yield epoxides. Suggest a mechanism for the reaction.

the=

PROBLEM 19-42 Propose a mechanism for the following reaction.

the=

PROBLEM 19-43 Paraldehyde, a sedative and hypnotic agent, is prepared by treatment of acetaldehyde with an acidic catalyst. Propose a mechanism for the reaction.

three=

PROBLEM 19-44 The Meerwein–Ponndorf–Verley reaction involves reduction of a ketone by treatment with an excess of aluminum triisopropoxide, [(CH₃)₂CHO]₃Al. The mechanism of the process is closely related to the Cannizzaro reaction in that a hydride ion acts as a leaving group. Propose a mechanism.

the=

PROBLEM 19-45 Propose a mechanism to account for the formation of 3,5-dimethylpyrazole from hydrazine and 2,4-pentanedione. What has happened to each carbonyl carbon in going from starting material to product.

the=

PROBLEM 19-46 In light of your answer to Problem 19-45, propose a mechanism for the formation of 3,5-dimethylisoxazole from hydroxylamine and 2,4-pentanedione.

the=

PROBLEM 19-47 Trans alkenes are converted into their cis isomers and vice versa on epoxidation followed by treatment of the epoxide with triphenylphosphine. Propose a mechanism for the reaction.

trans=

PROBLEM 19-48 Treatment of an α,β-unsaturated ketone with basic aqueous hydrogen peroxide yields an epoxy ketone. The reaction is specific to unsaturated ketones; isolated alkene double bonds do not react. Propose a mechanism.

the=

PROBLEM 19-49 One of the biological pathways by which an amine is converted to a ketone involves two steps: (1) oxidation of the amine by NAD⁺ to give an imine and (2) hydrolysis of the imine to give a ketone plus ammonia. Glutamate, for instance, is converted by this process into α-ketoglutarate. Show the structure of the imine intermediate, and propose mechanisms for both steps.

PROBLEM 19-50 Primary amines react with esters to yield amides: RCO₂R′ + R″NH₂ → RCONHR″ + R′OH. Propose a mechanism for the following reaction of an α,β-unsaturated ester.

the=

PROBLEM 19-51 When crystals of pure α-glucose are dissolved in water, isomerization occurs slowly to produce β-glucose. Propose a mechanism for the isomerization.

the=

PROBLEM 19-52 The Wharton reaction converts an epoxy ketone to an allylic alcohol by reaction with hydrazine. Review the Wolff–Kishner reaction in Section 19.9 and then propose a mechanism.

wharton=

Naming Aldehydes and Ketones

PROBLEM 19-53 Draw structures corresponding to the following names:

(a) Bromoacetone (b) (S)-2-Hydroxypropanal (c) 2-Methyl-3-heptanone (d) (2S,3R)-2,3,4-Trihydroxybutanal (e) 2,2,4,4-Tetramethyl-3-pentanone (f) 4-Methyl-3-penten-2-one (g) Butanedial (h) 3-Phenyl-2-propenal (i) 6,6-Dimethyl-2,4-cyclohexadienone (j) p-Nitroacetophenone

PROBLEM 19-54 Draw and name the seven aldehydes and ketones with the formula C₅H₁₀O. Which are chiral?

PROBLEM 19-55 Give IUPAC names for the following compounds:

(b)

(c)

(d)

(e)

(f)

PROBLEM 19-56

(b) An α-diketone (c) An aromatic ketone, C₉H₁₀O (d) A diene aldehyde, C₇H₈O

Reactions of Aldehydes and Ketones

PROBLEM 19-57

NaBH₄, then H₃O⁺

(b) Dess–Martin reagent (c) NH₂OH, HCl catalyst (d) CH₃MgBr, then H₃O⁺ (e) 2 CH₃OH, HCl catalyst (f) H₂NNH₂, KOH (g) (C₆H₅)₃P $\text{=$ $\text{=$ ₂ (h) HCN, KCN

(b)

1-Butanol (c) 1-Phenylcyclohexanol (d) Diphenylmethanol

(b)

(c)

(d)

PROBLEM 19-62 How would you synthesize the following substances from benzaldehyde and any other reagents needed? (a)

(b)

(c)

PROBLEM 19-63

(a) (CH₃)₂Cu^–Li⁺, then H₃O⁺

LiAlH₄, then H₃O⁺

(c) CH₃NH₂ (d) C₆H₅MgBr, then H₃O⁺ (e) H₂/Pd (f) HOCH₂CH₂OH, HCl (g) (C₆H₅)₃ $\mathop {\rm{P}}\limits^ +$ $\mathop {\rm{C}}\limits^ −$ HCH₃

1-Methylcyclohexene

(b) 2-Phenylcyclohexanone (c) cis-1,2-Cyclohexanediol (d) 1-Cyclohexylcyclohexanol

Spectroscopy

(b)

(c)

(d)

(a)

(b)

(c)

(d)

PROBLEM 19-68 Propose structures for molecules that meet the following descriptions. Assume that the kinds of carbons (1°, 2°, 3°, or 4°) have been assigned by DEPT–NMR. (a)

C₆H₁₂O; IR: 1715 cm^–1; ¹³C NMR: 8.0 δ (1°), 18.5 δ (1°), 33.5 δ (2°), 40.6 δ (3°), 214.0 δ (4°) (b)

C₅H₁₀O; IR: 1730 cm^–1; ¹³C NMR: 22.6 δ (1°), 23.6 δ (3°), 52.8 δ (2°), 202.4 δ (3°) (c) C₆H₈O; IR: 1680 cm^–1; ¹³C NMR: 22.9 δ (2°), 25.8 δ (2°), 38.2 δ (2°), 129.8 δ (3°), 150.6 δ (3°), 198.7 δ (4°)

Compound A, C₈H₁₀O₂, has an intense IR absorption at 1750 cm^–1 and gives the ¹³C NMR spectrum shown. Propose a structure for A.

1H NMR spectra: (a)

C₄H₇ClO

IR: 1715 cm^–1

(b) C₇H₁₄O

IR: 1710 cm^–1

General Problems

When 4-hydroxybutanal is treated with methanol in the presence of an acid catalyst, 2-methoxytetrahydrofuran is formed. Explain.

4-hydroxybutanal= The S_N2 reaction of (dibromomethyl)benzene, C₆H₅CHBr₂, with NaOH yields benzaldehyde rather than (dihydroxymethyl)benzene, C₆H₅CH(OH)₂. Explain. Reaction of 2-butanone with HCN yields a chiral product. What stereochemistry does the product have? Is it optically active?

The amino acid methionine is biosynthesized by a multistep route that includes reaction of an imine of pyridoxal phosphate (PLP) to give an unsaturated imine, which then reacts with cysteine. What kinds of reactions are occurring in the two steps?

o-succinylhomoserine-=

(b)

(c)

Tamoxifen is a drug used in the treatment of breast cancer. How would you prepare tamoxifen from benzene, the following ketone, and any other reagents needed?

ketone= Compound A, MW = 86, shows an IR absorption at 1730 cm^–1 and a very simple ¹H NMR spectrum with peaks at 9.7 δ (1 H, singlet) and 1.2 δ (9 H, singlet). Propose a structure for A. Compound B is isomeric with A (Problem 19-78) and shows an IR peak at 1715 cm^–1. The ¹H NMR spectrum of B has peaks at 2.4 δ (1 H, septet, J = 7 Hz), 2.1 δ (3 H, singlet), and 1.2 δ (6 H, doublet, J = 7 Hz). What is the structure of B?

The ¹H NMR spectrum shown is that of a compound with the formula C₉H₁₀O. How many double bonds and/or rings does this compound contain? If the unknown compound has an IR absorption at 1690 cm^–1, what is a likely structure?

proton=

The ¹H NMR spectrum shown is that of a compound isomeric with the one in Problem 19-80. This isomer has an IR absorption at 1730 cm^–1. Propose a structure. [Note: Aldehyde protons (CHO) often show low coupling constants to adjacent hydrogens, so the splitting of aldehyde signals is not always apparent.]

proton=

1H NMR spectra: (a)

C₉H₁₀O₂: IR: 1695 cm^–1

proton=

(b)

C₄H₆O: IR: 1690 cm^–1

Proton spectrum shows shifts of 0 (T M S), 1.86 (singlet), 6.00 (singlet), 6.31 (singlet), and 9.57 (singlet). Relative areas are 3.00, 1.00, 1.00, and 1.00 respectively.

1H NMR spectra.

(a) C₁₀H₁₂O: IR: 1710 cm^–1

proton=

(b) C₆H₁₂O₃: IR: 1715 cm^–1

Proton spectrum shows shifts of 0 (T M S), 2.18 (singlet), 2.74 (doublet), 3.37 (singlet), and 4.79 (triplet). Relative areas are 3.00, 2.00, 6.00, and 1.00 respectively.

When glucose (Problem 19-51) is treated with NaBH₄, reaction occurs to yield sorbitol, a polyalcohol commonly used as a food additive. Show how this reduction occurs.

alpha-glucose=

The proton and carbon NMR spectra for each of three isomeric ketones with the formula C₇H₁₄O are shown. Assign a structure to each pair of spectra.

c-13= Proton spectrum with shifts around 0.95 (triplet), around 1.6 (sextet), and around 2.35 (triplet). Relative areas indicated with integral lines are 2.91, 2.00, and 1.96 respectively. Carbon spectrum B displays peaks: spiky line at 218.40, unevenly shaded peaks at 80 delta for C D C l 3, medium-length peak at 38.85, and tall peak at 18.55. Proton spectrum with shifts around 1.1 (doublet) and around 2.8 (septet). Relative areas indicated with integral lines are 6.18 and 1.04 respectively. Carbon spectrum C shows peaks at 218.31, 75 delta (C D C l 3), 55.98, set between 29 to 32.5 delta, and expanded view with peaks at 32.27, 30.88, 29.73. Proton spectrum with shifts around 1.0 (singlet), 2.15 (singlet), and 2.35 (singlet). Relative areas indicated with integral lines are 8.91, 2.98, and 1.95 respectively.

The proton NMR spectrum for a compound with formula C₁₀H₁₂O₂ is shown below. The infrared spectrum has a strong band at 1711 cm^–1. The broadband-decoupled 13C NMR spectral results are tabulated along with the DEPT-135 and DEPT-90 information. Draw the structure of this compound.

proton=

Search

Text Color

Text Size

Margin Size

Font Type