Would you expect acetate ion (CH3CO2−) to be a better nucleophile in an SN2 reaction with an alkyl halide carried out in methanol or in dimethyl sulfoxide?
Verified step by step guidance
1
Identify the nature of the solvent: Methanol is a protic solvent, which means it can form hydrogen bonds with nucleophiles, potentially hindering their reactivity. Dimethyl sulfoxide (DMSO) is an aprotic solvent, which does not form hydrogen bonds with nucleophiles, allowing them to remain more reactive.
Understand the effect of solvent on nucleophilicity: In protic solvents like methanol, the nucleophile's negative charge is partially stabilized by hydrogen bonding with the solvent, which can decrease its reactivity. In aprotic solvents like DMSO, the nucleophile's full negative charge is available for reaction, enhancing its reactivity.
Consider the mechanism of the S<sub>N</sub>2 reaction: The S<sub>N</sub>2 mechanism involves a backside attack by the nucleophile on the electrophilic carbon of the alkyl halide, leading to inversion of configuration. The effectiveness of the nucleophile is crucial for this mechanism.
Analyze the role of the acetate ion: The acetate ion (CH<sub>3</sub>CO<sub>2</sub><sup>−</sup>) acts as the nucleophile in this reaction. Its effectiveness can vary significantly depending on the solvent used due to the reasons discussed in the previous steps.
Conclude on the better solvent for the reaction: Given that aprotic solvents enhance the reactivity of nucleophiles by allowing them to retain their full negative charge, dimethyl sulfoxide (DMSO) would be a more suitable solvent for an S<sub>N</sub>2 reaction involving the acetate ion as a nucleophile compared to methanol.
Recommended similar problem, with video answer:
Verified Solution
This video solution was recommended by our tutors as helpful for the problem above
Video duration:
2m
Play a video:
Was this helpful?
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Nucleophilicity
Nucleophilicity refers to the ability of a species to donate an electron pair to an electrophile, forming a chemical bond. It is influenced by factors such as charge, electronegativity, and solvent effects. In general, negatively charged species like acetate ion are stronger nucleophiles than their neutral counterparts. Understanding nucleophilicity is crucial for predicting the outcome of nucleophilic substitution reactions.
The choice of solvent can significantly impact the rate and mechanism of nucleophilic substitution reactions. Protic solvents, like methanol, can stabilize nucleophiles through hydrogen bonding, potentially reducing their reactivity. In contrast, aprotic solvents, such as dimethyl sulfoxide (DMSO), do not form strong hydrogen bonds with nucleophiles, often enhancing their nucleophilicity. Recognizing how solvents influence nucleophilic behavior is essential for understanding reaction conditions.
The S<sub>N</sub>2 mechanism is a type of nucleophilic substitution reaction characterized by a single concerted step where the nucleophile attacks the electrophile, leading to the displacement of a leaving group. This bimolecular process is favored by strong nucleophiles and less sterically hindered substrates. Familiarity with the S<sub>N</sub>2 mechanism helps in predicting reaction pathways and understanding the factors that influence reaction rates.