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Chapter 20: Q13P. (page 1062)

Most of the Fischer esterification mechanism is identical with the mechanism of acetal formation. The difference is in the final step, where a resonance-stabilized carbocation loses a proton to give the ester. Write mechanisms for the following reactions, with the comparable steps directly above and below each other. Explain why the final step of the esterification (proton loss) cannot occur in acetal formation, and show what happens instead.

Short Answer

Expert verified

In the formation of acetal from aldehyde, the loss of H+cannot take place to form carbonyl, and in the formation of ester from acid, the loss of H+ takes place to form carbonyl.

Step by step solution

01

Fischer esterification

Fischer esterification is the conversion of carboxylic acid to ester, and this reaction takes place in the presence of a strong acid and excess alcohol.The solvent used in these reactions is methanol or ethanol.

02

Mechanism of the reaction

The major difference between these two reactions is the loss of H+. In the formation of acetal from aldehyde, the loss of H+ cannot take place to form carbonyl, and in the formation of ester from acid, the loss of H+ takes place to form carbonyl.

Mechanism of both reactions

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Most popular questions from this chapter

Show how you would synthesize the following compounds, starting with acetylene and any compounds containing no more than four carbon atoms.

(a)hex-1-yne

(b)hex-2-yne

(c)cis-hex-2-ene

(d)trans-hex-2-ene

(e)1,1-dibromohexane

(f)2,2-dibromohexane

(g)pentanal, CH3CH2CH2CH2CHO

(h)pentan-2-one, CH3-CO-CH 2CH2 CH3

(i) (+/)-3,4-dibromohexane

(j)meso-butan-2,3-diol

(k)2-methylhex-3-yn-2-ol

Use chemical equations to show how the following accidents cause injury to the clothing involved (not to mention the skin under the clothing!)

  1. An industrial chemist spills aqueous H2SO4on her nylon stockings but fails to wash it off immediately.
  2. An organic laboratory student spills aqueous NaOHon his polyester slacks.

Question: What do the following pKa values tell you about the electron-withdrawing abilities of nitro, cyano, chloro, and hydroxy groups?

Which of the following compounds are chiral? Draw each compound in its most symmetric conformation, star any asymmetric carbon atoms, and draw any mirror planes. Label any meso compounds. You may use Fischer projections if you prefer.

(a) meso-2,3-dibromo-2,3-dichlorobutane

(b) -2,3-dibromo-2,3-dichlorobutane

(c) (2R,3S)-2-bromo-3-chlorobutane

(d) (2R,3S)-2,3-dibromobutane

(e) (R,R)-2,3-dibromobutane

(f)

(g)

(h)

Glutathione (GSH) is a tripeptide that serves as a mild reducing agent to detoxify peroxides and maintain the cysteine residues of hemoglobin and other red blood cell proteins in the reduced state. Complete hydrolysis of glutathione gives Gly, Glu, and Cys. Treatment of glutathione with carboxypeptidase gives glycine as the first free amino acid released. Treatment of glutathione with 2,4-dinitrofluorobenzene (Sanger reagent, Problem 24-21, page 1282), followed by complete hydrolysis, gives the 2,4-dinitrophenyl derivative of glutamic acid. Treatment of glutathione with phenyl isothiocyanate does not give a recognizable phenylthiohydantoin, however.

(a) Propose a structure for glutathione consistent with this information. Why would glutathione fail to give a normal product from Edman degradation, even though it gives a normal product from the Sanger reagent followed by hydrolysis?

(b) Oxidation of glutathione forms glutathione disulfide(GSSG). Propose a structure for glutathione disulfide, and write a balanced equation for the reaction of glutathione with hydrogen peroxide.

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