Textbook Question
Propose a mechanism for each of the following reactions:
a.
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12. Alcohols, Ethers, Epoxides and Thiols
Ether Cleavage
4:52 minutesProblem 15d
Textbook Question
Predict the products of the following reactions. An excess of acid is available in each case.
(d) 
Verified step by step guidance1
Step 1: Analyze the structure of the reactant. The reactant is a cyclic ether (specifically, a benzopyran structure) with an oxygen atom in a six-membered ring fused to a benzene ring.
Step 2: Recognize the role of HI (hydroiodic acid) in the reaction. HI is a strong acid and a source of iodide ions (I⁻). It can protonate the oxygen atom in the ether, making it susceptible to cleavage.
Step 3: Protonation of the oxygen atom occurs first. The lone pair of electrons on the oxygen atom interacts with the hydrogen ion (H⁺) from HI, forming a positively charged oxonium ion.
Step 4: The bond between the oxygen atom and one of the adjacent carbon atoms breaks, leading to the formation of two products. The iodide ion (I⁻) attacks the positively charged carbon atom, resulting in the formation of an alkyl iodide.
Step 5: The other product formed is a phenol group (benzene ring with an -OH group attached) due to the cleavage of the ether bond. The final products are phenol and an alkyl iodide.
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Video duration:
4mKey Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Acid-Base Reactions
Acid-base reactions involve the transfer of protons (H+) between reactants. In organic chemistry, acids can donate protons, while bases accept them. Understanding the role of acids in promoting reactions, especially in the presence of excess acid, is crucial for predicting the products formed in various organic transformations.
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The Lewis definition of acids and bases.
Reaction Mechanisms
A reaction mechanism outlines the step-by-step process by which reactants convert into products. It includes the formation and breaking of bonds, intermediates, and transition states. Familiarity with common mechanisms, such as nucleophilic substitution or electrophilic addition, is essential for predicting the outcome of reactions, especially when excess reagents are involved.
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Functional Group Transformations
Functional groups are specific groups of atoms within molecules that determine their chemical reactivity. In organic reactions, the presence of certain functional groups can dictate the type of reaction that occurs. Recognizing how excess acid can affect functional groups, such as converting alcohols to alkyl halides or facilitating esterification, is vital for predicting reaction products.
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