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Chapter 27: Problem 82

Which of the following is the strongest nucleophile for an \(S_{N} 2\) reaction? (a) \(\mathrm{H}_{2} \mathrm{O} ;\) (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH};\) (c) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{O}^{-} ;\) (d) \(\mathrm{CH}_{3} \mathrm{CO}_{2}{^-} ;\) (e) \(\mathrm{CH}_{3} \mathrm{S}^{-}\)

Short Answer

Expert verified
The strongest nucleophile among these for an \(S_{N}2\) reaction is \(\mathrm{CH}_{3}\mathrm{S}^{-}\) (option e).

Step by step solution

01

Understanding Nucleophilicity

Nucleophiles favorably interact with electrophiles to form chemical bonds by donating electronic density. They are species that have at least one lone pair of electrons which can be donated. The more readily these electrons can be donated, the stronger the nucleophile.
02

Analyzing Given Options

The question asks to determine the strongest nucleophile for an \(S_{N}2\) reaction, implying the solvent is aprotic (as these are commonly used in \(S_{N}2\) reactions). Given this, nucleophilicity parallels basicity. Thus \(\mathrm{CH}_{3}\mathrm{S}^{-}\) (option e) is the strongest nucleophile due to sulfur's less electronegativity and larger atomic radius compared to oxygen, making it more readily donate its electrons.
03

Considering Steric Hindrance

Steric hindrance can impair the ability of a molecule to act as a nucleophile. However, in this case, as all the molecules have the same number of atoms and methyl groups, it is not a critical factor for this analysis.

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Most popular questions from this chapter

In the chlorination of \(\mathrm{CH}_{4},\) some \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Cl}\) is obtained as a product. Explain why this should be so.

The reduction of aldehydes and ketones with a suitable hydride-containing reducing agent is a good way of synthesizing alcohols. This approach would be even more effective if, instead of a hydride, we could use a source of nucleophilic carbon. Attack by a carbon atom on a carbonyl group would give an alcohol and simultaneously form a carbon-to-carbon bond. How can we make a C atom in an alkane nucleophilic? This was achieved by Victor Grignard, who created the organometallic reagent \(\mathrm{R}-\mathrm{MgBr},\) with the following reaction in diethyl ether: $$\mathrm{R}-\mathrm{Br}+\mathrm{Mg} \longrightarrow \mathrm{R}-\mathrm{MgBr}$$ The Grignard reagent is rarely isolated. It is formed in solution and used immediately in the desired reaction. The alkylmetal bond is highly polar, with the partial negative charge on the \(\mathrm{C}\) atom, which makes the C atom highly nucleophilic. The Grignard reagent \((\mathrm{R}-\mathrm{MgBr})\) can attack a carbonyl group in an aldehyde or ketone as follows: Addition of dilute aqueous acid solution to the metal alkoxide furnishes the alcohol. The important synthetic consequence of this procedure is that we have prepared a product with more carbon atoms than present in the starting material. A simple starting material can be transformed into a more complex molecule. (a) What is the product of the reaction between methanal and the Grignard reagent formed from 1-bromobutane after the addition of dilute acid? (b) By using a Grignard reagent, devise a synthesis for 2-hexanol. (c) By using a Grignard reagent, devise a synthesis for 2 -methyl- 2 -hexanol. (d) Grignard reagents can also be formed with aryl halides, such as chlorobenzene. What would be the product of the reaction between the Grignard reagent of chlorobenzene and propanone? Can you think of an alternative synthesis of this product, again using a Grignard reagent? (e) The basicity of the \(C\) atom bound to the magnesium in the Grignard reagent can be used to make Grignard reagents of terminal alkynes. Write the equation of the reaction between ethylmagnesium bromide and 1-hexyne. [Hint: Ethane is evolved.] (f) By using a Grignard reagent, suggest a synthesis for 2 -heptyn-1-ol.

Starting with the compounds chloromethane, chloroethane, sodium azide, sodium cyanide, and a reducing agent, suggest how the following compounds could be synthesized. (a) \(N\) -methylpropanamide (b) ethylethanoate (c) methylethylamine (d) tetramethylammonium chloride

Write the formulas of the products formed from the reaction of 2 -butene with each of the following substances: (a) \(\mathrm{H}_{2} ;\) (b) \(\mathrm{Cl}_{2} ;\) (c) \(\mathrm{HCl} ;\) (d) \(\mathrm{H}_{2} \mathrm{O}\) (in acid).

Answer the following questions for this \(\mathrm{S}_{\mathrm{N}}1\) reaction: (a) What is the rate expression for the reaction? (b) Draw the reaction profile for the reaction. Label all parts. Assume that the products are lower in energy than the reactants. (c) What is the effect on the rate of the reaction of doubling the concentration of 1-bromo-1-methylpentane? (d) The solvent for the reaction is ethanol. What is the effect on the rate of the reaction of adding more ethanol?
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