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17 Reactions of Aromatic Compounds -- Part 15
The odd mass number of the ion and the even mass numbers of most fragments are what you should note.
The base peak has a resonance-stabilized iminium ion and a propyl radical.
The amine shown below isethylpropan-1 amine.
In contrast to other functional groups, we will study the reactions of amines first.
The approach is better because it involves the reactions of amine.
They start with an amine and add groups to make more amine.
We can easily understand how to use the reactions to convert simpler amines to more complicated amines by studying them first.
Amine attacks aldehydes and ketones.
An imine results when the attack is followed by dehydration.
The hydrazone and oxime are given by the same reaction of a hydrazine derivative.
We will use these reactions to make amines.
Arylamines and pyridine undergo aromatic changes that are important for amine synthesis.
In this section, we look at these replacements.
In an arylamine, the nonbonding electrons on nitrogen help keep intermediates stable.
There are two groups that are strong: ortho and para directors.
H can be found at the ortho or para positions.
The following reactions show the halogenation of aniline derivatives.
If an excess of reagent is used, all the unsubstituted positions become substituted.
Care must be exercised in reactions with aniline derivatives.
A full positive charge can be found in the ammonium salt that is given by strongly acidic reagents.
The NH+3 group is deactivating.
Strongly acidic reagents are not suitable for substitution of anilines.
Sometimes violent reactions can be caused by oxidizers such as nitric and sulfuric acids.
Section 19-12 will show how acylated the group can be used to decrease its basicity and allow substitution by a wide variety of electrophiles.
pyridine looks like a strongly deactivated benzene in its aromatic substitution reactions.
Friedel-Crafts reactions fail completely.
The positively charged intermediate can't be stable because its nonbonding electrons are close to the p system.
The meta substitution shown by deactivated benzene derivatives is analogous to the substitution shown by pyridine.
The substitution of pyridine is shown in mechanism 19-1.
There is an attack at the 3-position.
The product is given by the loss of a protons.
Attack at the 2-position is not observed.
An unstable intermediate can be found with one of the resonance structures showing a positive charge and only six electrons on nitrogen.
The positive charge spread over three carbon atoms gives a more stable intermediate in contrast to the negative charge spread over nitrogen.
The tendency of the nitrogen atom to attack and take on a positive charge hinders the substitution of pyridine.
The pyridinium ion is more resistant to substitution than the pyridine.
Show why this orientation is not observed by proposing a mechanism for nitration of pyridine at the 4-position.
There are two different types of pyridine shown here.
The yields are poor to fair and require severe conditions.
Explain why sulfonation occurs at the 3-position.
Pyridine is activated toward attack by nucleophilic aromatic substitution.
A nucleophile can attack and displace the leaving group if there is a good leaving group at either the 2-position or the 4-position.
The reaction shows a nucleophilic attack.
The negative charge on the nitrogen atom is delocalized.
If an attack occurs at the 3-position, stabilization is not possible.
A stabilizing intermediate is formed by aphilic attack at the 2-position.
The leaving group ispulsion gives the product.
There is a mechanism for the reaction of 2-bromopyridine with sodium amide.
When 3-bromopyridine is used, stronger reaction conditions are required and a mixture of 3-aminopyridine and 4-aminopyridine results.
There is a mechanism to explain the result.
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