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Chapter 12: Q26E (page 354)

Nonconjugated $β$ , $γ$ -unsaturated ketones, such as 3-cyclohexenone, are in an acid-catalyzed equilibrium with their conjugated $α$ , $β$ -unsaturated isomers. Propose a mechanism for this isomerization.

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01

Mechanism of the reaction

The mechanism of the given isomerization is

Mechanism

02

Explanation of the mechanism

The isomerization of 3-cyclohexanone to form 2-cyclohexanone takes place through the formation of its enol.

The acid protonates the carbonyl oxygen in the ketone. Then the partially positively charged hydrogen is abstracted, which forms the enol. Protonation of the enol with the electron pairs of oxygen yields a protonated 2-cyclohexenone. Lastly, deprotonation gives our desired product.

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Most popular questions from this chapter

Question: The infrared spectrum of the compound with the mass spectrum shown below lacks any significant absorption above $3000 {cm}^{- 1}$ . There is a prominent peak near $1740 {cm}^{- 1}$ and another strong peak near $1200 {cm}^{- 1}$ .Propose a structure consistent with the data.

Where might the following compounds have IR absorptions?

Most stable organic species have tetravalent carbon atoms, but species with trivalent carbon atoms also exist. Carbocations are one such class of compounds.

(a) How many valence electrons does the positively charged carbon atom have?

(b) What hybridization do you expect this carbon atom to have?

(c) What geometry is the carbocation likely to have?

Question: Write molecular formulas for compounds that show the following molecular ions in their high-resolution mass spectra, assuming that C, H, N, and O might be present. The exact atomic masses are: 1.00783 $({}^{1}H)$ , 12.00000 $({}^{12}C)$ , 14.00307 $({}^{14}N)$ , 15.99491 $({}^{16}O)$ .

$a) M^{+} = 98.0844 b) M^{+} = 123.0320$

Question: Ketones undergo a reduction when treated with sodium borohydride, ${NaBH}_{4}$ .What is the structure of the compound produced by reactionof 2-butanone with ${NaBH}_{4}$ if it has an IR absorption at $3400 {cm}^{- 1}$ and $M^{+} = 74$ in the mass spectrum?

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