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Chapter 10: Problem 124

Acetone \(\left(\mathrm{CH}_{3}\right) \mathrm{C}=\mathrm{O},\) a ketone, will react with a strong base \((\mathrm{A})\) to produce the enolate anion, \(\mathrm{CH}_{3}(\mathrm{C}=\mathrm{O}) \mathrm{CH}_{2}^{-} .\) Draw the Lewis structure of the enolate anion, and describe the relative contributions of any resonance structures.

Short Answer

Expert verified
The enolate anion Lewis structure consists of a double bond between the central carbon and the oxygen, and a single bond between the central carbon and two carbon atoms. One carbon atom (alpha) has a negative charge and two hydrogen atoms attached. It has two resonance structures where the second has the negative charge on oxygen, representing the delocalized charge.

Step by step solution

01

Formation of Enolate Anion

Acetone \(\left(\mathrm{CH}_{3}\right) \mathrm{C}=\mathrm{O}\) reacts with a strong base, donating a proton from the alpha carbon atom (one carbon atom away from the carbonyl group, C=O) to the base. This forms an enolate anion, \(\mathrm{CH}_{3}(\mathrm{C}=\mathrm{O}) \mathrm{CH}_{2}^{-}\), where there's a negative charge on the alpha carbon and a double bond between the central carbon and oxygen.
02

Drawing the Lewis Structure of the Enolate Anion

The Lewis structure starts with the acetone central framework \(\mathrm{H}_{3}\mathrm{C}-\mathrm{C}-\mathrm{CH}_{3}\) where the central carbon is double bonded to the oxygen and single bonded to a carbon atom that also has three hydrogen atoms bonded. The second carbon atom (alpha carbon), aside from being single-bonded to the central carbon, bears a negative charge and is also single bonded to two hydrogen atoms.
03

Resonance Structures Contribution

There are two important resonance structures in the anion enolate since the negative charge on alpha carbon can be delocalized on oxygen atom. In the second structure, the central carbon is single bonded to oxygen, and the oxygen bears the negative charge while the central carbon is double bonded to the alpha carbon. The two structures (canonical forms) contribute to the overall shape of the enolate.

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Most popular questions from this chapter

Assign formal charges to the atoms in the following species, and then select the more likely skeletal structure. (a) \(\mathrm{H}_{2} \mathrm{NOH}\) or \(\mathrm{H}_{2} \mathrm{ONH}\) (b) SCS or CSS (c) NFO or FNO (d) \(\mathrm{SOCl}_{2}\) or \(\mathrm{OSCl}_{2}\) or \(\mathrm{OCl}_{2} \mathrm{S}\) (e) \(\mathrm{F}_{3} \mathrm{SN}\) and \(\mathrm{F}_{3} \mathrm{NS}\)

Predict the shapes of the following molecules, and then predict which would have resultant dipolemoments: (a) \(\mathrm{SO}_{2} ;\) (b) \(\mathrm{NH}_{3} ;\) (c) \(\mathrm{H}_{2} \mathrm{S} ;\) (d) \(\mathrm{C}_{2} \mathrm{H}_{4} ;\) (e) \(\mathrm{SF}_{6}\); (f) \(\mathrm{CH}_{2} \mathrm{Cl}_{2}\).

One possibility for the electron-group geometry for seven electron groups is pentagonal-bipyramidal, as found in the IF \(_{7}\) molecule. Write the VSEPR notation for this molecule. Sketch the structure of the molecule, labeling all the bond angles.

Through appropriate Lewis structures, show that the phenomenon of resonance is involved in the nitrite ion.

Use the VSEPR theory to predict a probable shape of the molecule \(\mathrm{F}_{4} \mathrm{SCH}_{2}\), and explain the source of any ambiguities in your prediction.
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