Multiple Choice
For a 2nd order substitution reaction tripling the concentration of the substrate, R–X, and tripling the concentration of the nucleophile does what to the rate of the reaction?
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7. Substitution Reactions
SN2 Reaction
4:12 minutesProblem 14b
Textbook Question
Predict the major products of the following substitutions.
b. 
Verified step by step guidance1
Identify the type of reaction: This is a nucleophilic substitution reaction where sodium acetylide (HC≡C:- Na+) acts as a nucleophile, and 1-chlorobutane (CH3CH2CH2CH2Cl) is the alkyl halide.
Determine the mechanism: Since 1-chlorobutane is a primary alkyl halide, the reaction will proceed via the SN2 mechanism. In an SN2 reaction, the nucleophile attacks the electrophilic carbon directly, leading to a one-step displacement of the leaving group (Cl⁻).
Analyze the nucleophile: Sodium acetylide (HC≡C:- Na+) is a strong nucleophile due to the negatively charged carbon in the acetylide ion. This makes it highly reactive toward electrophilic carbons.
Describe the reaction: The acetylide ion (HC≡C:-) will attack the carbon atom bonded to the chlorine in 1-chlorobutane (CH3CH2CH2CH2Cl). This results in the displacement of the chloride ion (Cl⁻) and the formation of a new carbon-carbon bond between the acetylide ion and the butyl group.
Write the product: The major product will be a terminal alkyne with the structure HC≡C-CH2CH2CH2CH3, where the acetylide ion has replaced the chlorine atom in 1-chlorobutane.
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Video duration:
4mKey Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Nucleophilic Substitution
Nucleophilic substitution is a fundamental reaction in organic chemistry where a nucleophile attacks an electrophile, resulting in the replacement of a leaving group. In this case, sodium acetylide (HC≡C:- Na+) acts as the nucleophile, targeting the carbon atom bonded to the chlorine in 1-chlorobutane. Understanding the mechanism of this reaction, whether it follows an SN1 or SN2 pathway, is crucial for predicting the major products.
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Nucleophiles and Electrophiles can react in Substitution Reactions.
Alkyne Reactivity
Alkynes, such as sodium acetylide, are highly reactive due to the presence of a triple bond, which can participate in various reactions, including nucleophilic substitutions. The terminal alkyne (HC≡C:-) has a negative charge on the carbon, making it a strong nucleophile. Recognizing the reactivity of alkynes helps in predicting how they will interact with alkyl halides like 1-chlorobutane.
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Leaving Groups
A leaving group is an atom or group that can depart from the parent molecule during a chemical reaction, facilitating the formation of new bonds. In the context of the reaction with 1-chlorobutane, the chloride ion (Cl-) is the leaving group. The stability of the leaving group significantly influences the reaction's rate and the formation of products, making it essential to consider when predicting the outcome of nucleophilic substitutions.
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07:22The 3 important leaving groups to know.
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