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Chapter 20: Q20P. (page 1067)

Question: Propose a mechanism for conversion of the dianion to the ketone under mildly acidic conditions.

Short Answer

Expert verified

The mechanism for converting dianion to ketone is as follows:

Step by step solution

01

Dianion to ketone conversion

A dianion compound with two negative charges, when treated under mildly acidic conditions, converts into a hydrate of the ketone.A ketone is formed when water is cleaved from a hydrate of the ketone.

02

Conversion of dianion to ketone

A ketone hydrate is formed on treating dianion with two equivalents of acids. Again when treated with acid, water is removed, and a secondary cation is formed. On treating this secondary cation with water, a ketone product is formed.

Mechanism for the conversion of dianion to ketone

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Most popular questions from this chapter

Show how you would accomplish the following multistep syntheses. You may use any additional reagents and solvents you need.

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.

(a) How many asymmetric carbon atoms are there in an aldotetrose? Draw all the aldotetrose stereoisomers.

(b) How many asymmetric carbon atoms are there in a ketotetrose? Draw all the ketotetrose stereoisomers.

(c) How many asymmetric carbon atoms and stereoisomers are there for an aldohexose? For a ketohexose?

Question:

  1. The Key Mechanism for Fischer esterification omitted some important resonance forms of the intermediates shown in brackets. Complete the mechanism by drawing all the resonance forms of these two intermediates.
  2. Propose a mechanism for the acid-catalyzed reaction of acetic acid with ethanol to give ethyl acetate.
  3. The Principle of Microscopic Reversibility states that a forward reaction and a reverse reaction taking place under the same conditions (as in equilibrium) must follow the same reaction pathway in microscopic detail. The reverse of the Fischer esterification is the acid-catalyzed hydrolysis of an ester. Propose a mechanism for the acid-catalyzed hydrolysis of ethyl benzoate, PhCOOCH2CH3.

(a) The isoelectric point (pI) of phenylalanine is pH 5.5. Draw the structure of the major form of phenylalanine at pH values of 1,5.5, and 11.

(b) The isoelectric point of histidine is pH 7.6. Draw the structures of the major forms of histidine at pH values of 1, 4, 7.6, and 11. Explain why the nitrogen in the histidine ring is a weaker base than the伪 -amino group.

(c) The isoelectric point of glutamic acid is pH 3.2. Draw the structures of the major forms of glutamic acid at pH values of 1, 3.2, 7, and 11. Explain why the side-chain carboxylic acid is a weaker acid than the acid group next to the-carbon atom.
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