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Ch.6 - Alkyl Halides; Nucleophilic Substitution
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook
All textbooksWade 9th EditionCh.6 - Alkyl Halides; Nucleophilic SubstitutionProblem 38b,c
Chapter 6, Problem 38b,c

When tert-butyl bromide is heated with an equal amount of ethanol in an inert solvent, one of the products is ethyl tert-butyl ether.
b. What happens to the rate if the concentration of tert-butyl bromide is tripled and the concentration of ethanol is doubled?
c. What happens to the rate if the temperature is raised?

Verified step by step guidance
1
Step 1: Recognize the reaction mechanism. The formation of ethyl tert-butyl ether from tert-butyl bromide and ethanol is an SN1 reaction. In an SN1 reaction, the rate-determining step is the formation of the carbocation intermediate, which depends only on the concentration of the alkyl halide (tert-butyl bromide).
Step 2: Analyze the effect of tripling the concentration of tert-butyl bromide. Since the rate of an SN1 reaction is directly proportional to the concentration of the alkyl halide, tripling the concentration of tert-butyl bromide will triple the reaction rate.
Step 3: Analyze the effect of doubling the concentration of ethanol. In an SN1 reaction, the concentration of the nucleophile (ethanol in this case) does not affect the rate of the reaction because the nucleophile participates in a step after the rate-determining step. Therefore, doubling the concentration of ethanol will not change the reaction rate.
Step 4: Consider the effect of raising the temperature. Increasing the temperature generally increases the reaction rate because it provides more energy for the molecules to overcome the activation energy barrier. This effect applies to all chemical reactions, including SN1 reactions.
Step 5: Summarize the findings. Tripling the concentration of tert-butyl bromide will triple the rate, doubling the concentration of ethanol will have no effect on the rate, and raising the temperature will increase the rate by accelerating the formation of the carbocation intermediate.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Reaction Rate

The reaction rate refers to the speed at which reactants are converted into products in a chemical reaction. It is influenced by factors such as concentration, temperature, and the presence of catalysts. In this context, understanding how changes in the concentrations of tert-butyl bromide and ethanol affect the rate of ether formation is crucial for predicting the outcome of the reaction.
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Concentration Effects

Concentration effects describe how the rate of a reaction can change with varying concentrations of reactants. According to the rate law, if the concentration of a reactant is increased, the rate of reaction typically increases, often in a proportional manner. In this case, tripling the concentration of tert-butyl bromide and doubling that of ethanol will likely lead to a significant increase in the reaction rate.
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Temperature Dependence

Temperature dependence in chemical reactions indicates that increasing the temperature generally increases the reaction rate. This is due to the increased kinetic energy of molecules, leading to more frequent and effective collisions. In the context of the question, raising the temperature would enhance the rate of ether formation by promoting faster molecular movement and higher energy interactions.
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Related Practice
Textbook Question

When ethyl bromide is added to potassium tert-butoxide, the product is ethyl tert-butyl ether.

CH3CH2–Br + (CH3)3C–O–K+ → (CH3)3C–O–CH2CH3 ethyl bromide potassium tert-butoxide ethyl tert-butyl ether

a. What happens to the reaction rate if the concentration of ethyl bromide is doubled?

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Textbook Question

Chlorocyclohexane reacts with sodium cyanide (NaCN) in ethanol to give cyanocyclohexane. The rate of formation of cyanocyclohexane increases when a small amount of sodium iodide is added to the solution. Explain this acceleration in the rate.

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Textbook Question

When tert-butyl bromide is heated with an equal amount of ethanol in an inert solvent, one of the products is ethyl tert-butyl ether.

a. What happens to the reaction rate if the concentration of ethanol is doubled?

1
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Textbook Question

When ethyl bromide is added to potassium tert-butoxide, the product is ethyl tert-butyl ether.

CH3CH2–Br + (CH3)3C–O–K+ → (CH3)3C–O–CH2CH3 ethyl bromide potassium tert-butoxide ethyl tert-butyl ether

b. What happens to the rate if the concentration of potassium tert-butoxide is tripled and the concentration of ethyl ­bromide is doubled?

c. What happens to the rate if the temperature is raised?

Textbook Question

Give the substitution products expected from solvolysis of each compound by heating in ethanol.

(c)

(d)

Textbook Question

Give the substitution products expected from solvolysis of each compound by heating in ethanol.

(a)

(b)

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