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4.9 Synthesis Strategies
Strategies for synthesis problems will be discussed in this section.
Let's review the reactions we have seen so far in this chapter.
Carefully look at the chart above and make sure that you know the reagents you would use to achieve each transformation.
If you can't remember the reagents, you won't be able to do synthesis problems.
Make sure you know how to install each group individually and take a close look at the groups on the ring.
The order of events should be considered.
The directing effects of the first group will determine where the next group will be installed.
The relative position of the two groups in the product will be affected by this consideration.
When you need to use sulfonation as a blocking technique, take steric effects into account.
There are other considerations, but they will help you with synthesis problems.
A simple knowledge of the reagents needed to install a group on a ring is the first consideration.
The electronics and sterics considerations can be summarized in this way.
You must always consider electronic and steric effects when you solve a problem.
You will find the same theme in every chapter as you progress through this course.
You must always consider electronic effects and steric effects.
We need to make sure we know how to install both groups.
We perform a nitration using sulfuric acid and nitric acid.
We must use Friedel-Crafts acylation and reduction to reduce the double bond.
Let's look at electronic considerations.
We should install the nitro group first.
We can't install the nitro group first.
We need to consider steric effects here.
There is a difficulty when we look at the steric effects.
The steric effects are not in our favor.
The order of events will be dictated by the limitation.
A Friedel-Crafts reaction can't be performed on a ring that is either moderately deactivated or strongly deactivated.
You can perform other reactions with deactivated rings, such as bromination, but not Friedel-Crafts reactions.
The nitro group can't be installed first.
You must always consider the order of events when trying to solve a synthesis problem.
There are two groups on the ring.
We need to know what reagents we would use to install each group.
We would use a Lewis acid to install bromine.
If we install an ethyl group on a ring, we don't need to worry about carbocation rearrangements because we can use a simple alkylation.
When we consider the effects of each substituent, we see a serious issue.
We don't use an acylation.
We will install an acyl group on the ring if we do that.
The bromine can be installed in the correct spot.
For each of the following, propose an efficient synthesis.
You could use a piece of paper to help you work through the problems.
We didn't cover everything in your textbook chapter.
There are a few reactions that we did not cover in your textbook chapter.
To learn those reactions, you will need to go through your notes and textbook.
We covered 80% of what you read in your textbook.
The purpose of this chapter is to serve as a foundation for your mastery of aromatic substitution.
If you went through this chapter, you should be comfortable with the steps involved in proposing mechanisms, predicting products, and proposing a synthesis.
You should know how to use directing effects.
You should know how to use steric effects.
You should be able to go through your textbook and lecture notes and polish off the rest of the material for your exam now that you have all of that as a foundation.
The foundation that we have developed in this chapter should make the content in your textbook seem easy.
There are problems in your textbook.
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