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Chapter 22: Problem 59

Propose a synthesis for the antihistamine \(p\)-methyldiphenhydramine, given this retrosynthetic analysis. Is \(p\)-methyldiphenhydramine chiral? If so, how many of the possible stereoisomers are formed in this synthesis?

Short Answer

Expert verified
If so, how many stereoisomers are formed in the synthesis process? Answer: To synthesize p-methyldiphenhydramine, we can follow these steps: 1. Start with the reaction of p-chlorobenzyl chloride (1-chloro-4-methylbenzene) with diphenylmethanol (benzhydrol). 2. Perform a Williamson ether synthesis, where the alcohol group on benzhydrol attacks the electrophilic carbon on p-chlorobenzyl chloride. This results in the displacement of the chloride anion and formation of an ether linkage between the benzhydrol and 1-chloro-4-methylbenzene. 3. The product formed in step 2 is p-methyldiphenhydramine. P-methyldiphenhydramine is chiral due to its stereogenic center at the carbon atom connecting the two aromatic rings. There are two possible stereoisomers for this molecule, R and S, as it has only one chiral center.

Step by step solution

01

Examine the Retrosynthetic Analysis

In order to propose a synthesis for p-methyldiphenhydramine, we need to examine the retrosynthetic analysis provided. A retrosynthetic analysis is a process used to determine the steps necessary to synthesize a target molecule by working backward from the target molecule to the starting materials. In this case, the target molecule is p-methyldiphenhydramine.
02

Propose Synthesis for p-Methyldiphenhydramine

The retrosynthetic analysis was not provided in this exercise, so we will propose a synthesis based on a standard approach to make diphenhydramine: 1. Start with the reaction of p-chlorobenzyl chloride (1-chloro-4-methylbenzene) with diphenylmethanol (benzhydrol). 2. In this Williamson ether synthesis, the alcohol group on benzhydrol attacks the electrophilic carbon on p-chlorobenzyl chloride, leading to the displacement of chloride anion and the formation of an ether linkage between the benzhydrol and 1-chloro-4-methylbenzene. 3. The product formed in step 2 is p-methyldiphenhydramine. At this point, we have proposed a synthesis for the target molecule. Next, we need to discuss its chirality and the number of possible stereoisomers.
03

Determine Chirality and Number of Stereoisomers

To determine whether p-methyldiphenhydramine is chiral, we need to examine its chemical structure. The molecule has a stereogenic center at the carbon atom connecting the two aromatic rings. This stereogenic center has four different substituents attached to it, resulting in chirality. Now that we have established that p-methyldiphenhydramine is chiral, we can discuss the number of stereoisomers formed in the synthesis. Since there is only one chiral center, there will be two possible stereoisomers for this molecule: R and S. In conclusion, the target molecule p-methyldiphenhydramine is chiral, and there are two possible stereoisomers formed in the given synthesis.

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Most popular questions from this chapter

Write the stepwise mechanism for sulfonation of benzene by hot, concentrated sulfuric acid. In this reaction, the electrophile is \(\mathrm{SO}_{3}\) formed as shown in the following equation. $$ \mathrm{H}_{2} \mathrm{SO}_{4} \rightleftharpoons \mathrm{SO}_{3}+\mathrm{H}_{2} \mathrm{O} $$

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