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16 -- Part 3: AROMATIC COMPOUNDS
Anisole quickly brominates in water without a catalyst, because a methoxy group is so strongly activated.
In the presence of bromine, this reaction proceeds.
A nitrogen atom with a nonbonding pair of electrons is a powerful group.
Aniline undergoes a bromination in bromine water without a catalyst.
The 2,4,6-tribromoaniline ring is more electron-rich than anisole.
If an attack takes place ortho or para, nitrogen's nonbonding electrons provide resonance stabilization to the sigma complex.
The complexes sigma related to bromination of aniline at the ortho, meta, and para positions are drawn.
A sigma complexample can be provided by substituent with a lone pair of electrons on the atom bonding to the ring.
All of these substituents are para-directing.
The bromine color in both beakers is gone.
nitration of nitrobenzene requires concentrated nitric and sulfuric acids.
The meta isomer is the major product.
The results should not be surprising.
The carbon atoms ortho and para are affected by a substituent on a benzene ring.
The ortho and para positions are primarily activated by an electron-donating substituent and an electron-drawing substituent.
The products have meta substitution and the meta positions are the most reactive.
The nitrogen atom has a positive charge no matter how we position the electrons.
The positively charged nitrogen withdraws electron density from the aro aromatic ring.
The aromatic ring is less electron-rich than benzene, so it is deactivated.
The deactivating effect is strongest at ortho reactions.
Each sigma complex has a positive charge spread over three carbon atoms.
This close proximity of two positive charges is not stable.
Positive charges are farther apart.
NO2 is a meta-director.
The reaction rates for NO2 are slower than for benzene.
Most deactivating sub stituents are meta-directors.
Deactivating substituents are groups with a positive charge on the atom of the aromatic ring.
The only sigma complexes that don't put a positive charge on this ring shells are the safer high explosives and meta substitution complexes.
It is sensitive to shock carbon.
The ring has a positive charge on it.
The reaction with benzene is quicker than the meta position.
There are some common substituents listed in the summary table.
The forms show how the atom bonds to the aromatic ring.
Aniline reacts quickly with bromine to give 2,4,6-tribromoaniline.
They are poor.
Explain why nitration of aniline is so slow.
Although nitration of aniline is slow, it goes quickly and gives mostly para substitution.
There is a difference in reactivity.
The general rules do not apply to the halobenzenes.
There are groups that are deactivating and there are groups that are para-directors.
There are two effects that oppose each other.
The X bond has a carbon atom at the positive end of the dipole.
The benzene ring has less electron-rich making it less reactive.
The positive charge of the sigma complex is shared by the carbon atom and the halogen.
Even though it is sigma-withdrawing, the resonance stabilization allows a halogen to be pi-donating.
The sigma complex is not delocalized onto the carbon atom because of the reaction at the meta position.
The meta intermediate is not stable by the ion structure.
There is a preference for ortho and para substitution in the nitration of chlorobenzene.
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