Textbook Question
Show how you would convert propan-1-ol to the following compounds using tosylate intermediates. You may use whatever additional reagents are needed.
a. 1-bromopropane
b. propan-1-amine, CH3CH2CH2NH2
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12. Alcohols, Ethers, Epoxides and Thiols
Leaving Group Conversions - Sulfonyl Chlorides
Problem 27
Textbook Question
On the reaction coordinate diagram for the disfavored nucleophilic displacement of hydroxide, predict the curve that would demonstrate how using a tosylate makes the substitution favorable.
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Verified step by step guidance1
Begin by understanding the reaction coordinate diagram, which plots the energy changes during a chemical reaction. The x-axis represents the progress of the reaction, while the y-axis represents the energy level.
Identify the initial state of the reactants and the final state of the products on the diagram. For a disfavored nucleophilic displacement of hydroxide, the energy of the transition state is typically high, making the reaction less favorable.
Introduce the concept of a tosylate group. Tosylates are excellent leaving groups due to their ability to stabilize the negative charge, thus lowering the energy of the transition state.
Predict how the curve would change with the use of a tosylate. The energy barrier (activation energy) should decrease, making the transition state lower in energy compared to the original reaction with hydroxide.
Visualize the new curve on the diagram. The curve should show a lower peak for the transition state, indicating a more favorable reaction pathway with the tosylate as the leaving group.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Reaction Coordinate Diagram
A reaction coordinate diagram is a graphical representation of the energy changes that occur during a chemical reaction. It plots the potential energy of the system as the reaction progresses from reactants to products. Key features include the energy of activation, transition states, and the overall energy change, which help in understanding the reaction's kinetics and thermodynamics.
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Nucleophilic Substitution
Nucleophilic substitution is a fundamental type of reaction in organic chemistry where a nucleophile replaces a leaving group in a molecule. The reaction can proceed via two main mechanisms: SN1, which involves a two-step process with a carbocation intermediate, and SN2, which is a one-step bimolecular process. The nature of the nucleophile, leaving group, and substrate significantly influences the reaction pathway and rate.
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Tosylate as a Leaving Group
Tosylate (p-toluenesulfonate) is a superior leaving group compared to hydroxide due to its ability to stabilize the negative charge through resonance and its large size, which disperses charge. In nucleophilic substitution reactions, replacing a poor leaving group like hydroxide with tosylate can make the reaction more favorable by lowering the activation energy, thus enhancing the reaction rate and yield.
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