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Chapter 20: Q41P (page 1076)

In the presence of a trace of acid, δ-hydroxyvaleric acid forms a cyclic ester (lactone).

HO-CH2CH2CH2CH2-COOH

δ-hydroxyvaleric acid

(a)Give the structure of the lactone, called δ-valerolactone.

(b) Propose a mechanism for the formation of δ-valerolactone.

Short Answer

Expert verified

The organic compound that has hydroxyl group and COH group at the terminals of the five-membered acyclic parent chain is hydroxyvaleric acid.

This compound is also called 5-hydroxypentanoic acid.

Step by step solution

01

About hydroxyvaleric acid

The organic compound that has hydroxyl group and COH group at the terminals of the five-membered acyclic parent chain is hydroxyvaleric acid.

This compound is also called 5-hydroxypentanoic acid.

02

About the reaction

The five-membered acyclic compound becomes a six-membered ring when hydroxyvaleric acid is treated with a trace of acid. The ring contains one oxygen atom in place of carbon and one carbonyl group attached to the ring.

The structure is given below.

Structure of δ-valerolactone

03

About the mechanism

The lone pair of electrons present in the carbonyl oxygen attacks the acid leading to the resonance structures.

On rearrangement, there will be the development of a positive charge on the oxygen which is then attacked by an anion followed by the attack of acid. The removal of water forms the desired product.

Mechanism of the reaction

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Most popular questions from this chapter

An enolate is a very strong nucleophile. Bromine is a strong electrophile, so it can react with much weaker nucleophiles. Give mechanisms for the reactions of bromine with cyclopentene and with phenol, which are both much weaker nucleophiles than an enolate.

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) Propose a mechanism for the following reaction:

(b) Use the bond-dissociation enthalpies given in Table 4-2 (page 203) to calculate the value of ∆H° for each step shown in your mechanism. (The BDE for is about 280 kJ/mol, or 67 kcal/mol.) Calculate the overall value of ∆H° for the reaction. Are these values consistent with a rapid free-radical chain reaction?

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

Show how you would synthesize the following compounds from the appropriate carboxylic acids or acid derivatives.

a)

b)

c)
See all solutions

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