
(a)
Interpretation:
The complete, detailed mechanism of the given reaction in the acidic medium is to be drawn, and major organic product is to be predicted.
Concept introduction:
When an

Answer to Problem 18.56P
The complete, detailed mechanism of the given reaction in the acidic medium is shown below; an acetal is the major product.
Explanation of Solution
The given reaction is
This is an acetal formation reaction in which the reaction is catalyzed by an acid, and the excess
First three steps are that of the acid catalyzed nucleophilic addition reactions on ketone. In the first step, the
Next, the weak nucleophile, diol, attacks the activated electrophilic carbon by nucleophilic addition reaction.
In the next step, deprotonation produces the uncharged hemiacetal.
The remaining steps essentially make up the
The
The resonance stabilized carbocation is further attacked by the diol nucleophile, which produces positively charged acetal. The carbonation step is intramolecular because it forms a five-membered ring, and it is stable.
In the last step, the deprotonation of the charged acetal by alcohol results in the uncharged acetal formation. Acetal is the major product of the given aldehyde.
The complete, detailed mechanism of the given reaction in the acidic medium is shown below; an acetal is the major product.
The complete, detailed mechanism of the given reaction under acidic medium and excess alcohol is drawn.
(b)
The complete, detailed mechanism of the given reaction in the acidic medium is to be drawn, and major organic product is to be predicted.
Concept introduction:
When an aldehyde or ketone is treated with an alcohol under acidic conditions, a hemiacetal product is formed. Use of an excess amount of alcohol under acidic conditions and after that the nucleophilic addition produces hemiacetals, which further form an acetal. The acetal has two alkoxy groups bonded to the same carbon. The formation of the acetal product is favored by using excess alcohol. This type of reactions is carried forward by proton transfer and nucleophilic addition on the carbonyl carbon. An acetal is produced under acidic conditions by a ketone or aldehyde but not under basic conditions because the nucleophilic substitution requires the leaving group to be

Answer to Problem 18.56P
The complete, detailed mechanism of the given reaction in the acidic medium is shown below; an acetal is the major product.
Explanation of Solution
The given reaction is
This is an acetal formation reaction in which the reaction is catalyzed by sulfuric acid, and the excess diols act as the nucleophile.
First three steps are that of the acid catalyzed nucleophilic addition reactions on ketone. In the first step, the
Next, the weak nucleophile, alcohol, attacks the activated electrophilic carbon by nucleophilic addition reaction.
In the next step, deprotonation produces the uncharged hemiacetal.
The remaining steps essentially make up an
The
The resonance stabilized carbocation is further attacked by the diol nucleophile, which produces positively charged acetal. The carbonation step is intramolecular because it forms a five-membered ring, and it is stable.
In the last step, the deprotonation of charged acetal by alcohol results in the uncharged acetal formation. Acetal is the major product of the given aldehyde.
The complete, detailed mechanism of the given reaction in the acidic medium is shown below; an acetal is the major product.
The complete, detailed mechanism of the given reaction under acidic medium and excess alcohol is drawn.
(c)
Interpretation:
The complete, detailed mechanism of the given reaction in the acidic medium is to be drawn, and major organic product is to be predicted.
Concept introduction:
When an aldehyde or ketone is treated with an alcohol under acidic conditions, a hemiacetal product is formed. Use of an excess amount of alcohol under acidic conditions and after that the nucleophilic addition produces hemiacetals, which further form an acetal. The acetal has two alkoxy groups bonded to the same carbon. The formation of the acetal product is favored by using excess alcohol. This type of reactions is carried forward by proton transfer and nucleophilic addition on the carbonyl carbon. An acetal is produced under acidic conditions by a ketone or aldehyde but not under basic conditions because the nucleophilic substitution requires the leaving group to be

Answer to Problem 18.56P
The complete, detailed mechanism of the given reaction in the acidic medium is shown below; an acetal is the major product.
Explanation of Solution
The given reaction is
This is an acetal formation reaction in which the reaction is catalyzed by sulfuric acid, and the excess diol acts as the nucleophile.
First three steps are that of the acid catalyzed nucleophilic addition reactions on the aldehyde. In the first step, the
Next, the weak nucleophile, alcohol, attacks the activated electrophilic carbon by nucleophilic addition reaction.
In the next step, deprotonation produces the uncharged hemiacetal.
The remaining steps essentially make up an
The
The resonance stabilized carbocation is further attacked by the diol nucleophile, which produced positively charged acetal. The carbonation step is intramolecular because it forms a six-membered ring, and it is stable.
In the last step, the deprotonation of the charged acetal by alcohol results in the uncharged acetal formation. Acetal is the major product of the given aldehyde.
The complete, detailed mechanism of the given reaction in the acidic medium is shown below; an acetal is the major product.
The complete, detailed mechanism of the given reaction under acidic medium and excess alcohol is drawn.
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Chapter 18 Solutions
Organic Chemistry: Principles and Mechanisms (Second Edition)
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