Edited Invalid date
16 -- Part 6: AROMATIC COMPOUNDS
Polyalkylation is a problem.
The acylbenzene does not react further after the acylation.
A two-step sequence can make many alkylbenzenes that are impossible to make by direct alkylation.
Friedel-Crafts alkylation cannot makepropylbenzene.
There are two things that give isopropylbenzene, together with some diisopropylbenzene.
The conditions used to reduce a nitro group to an amine are similar to those used for the Clemmensen reduction.
In the following synthesis, aromatic substitution followed by reduction is used to make compounds with specific substitution patterns.
Friedel- Crafts reactions use carboxylic acids and acid anhydride as acylating agents.
When we study the reactions of carboxylic acids and their derivatives, we consider these acylating agents.
Friedel-Crafts acylation cannot add a formyl group to benzene.
Formyl chloride can't be bought or stored because it is unstable.
A mixture of carbon monoxide and HCl together with a catalyst consisting of cuprous chloride and aluminum chloride can be used for mylation.
The formyl cation could be generated through a small amount of formyl chloride.
The formyl benzene is a result of the reaction with benzene.
Friedel-Crafts acylations show how you can use Friedel-Crafts acylation, Clemmensen reduction, and/or free from Gatterman-Koch synthesis to prepare compounds.
If there are strong electron-withdrawing groups ortho or para to the halide, nucleophiles can displace it.
A strong nucleophile replaces a leaving group in aromatic substitution.
Aryl halides can't achieve the correct geometry for back-side displacement.
The back of the carbon bearing the halogen is blocked by the aromatic ring.
The mechanism can't be involved.
The reaction rate is proportional to the concentration of the nucleophile.
The ratelimiting step must involve the nucleophile.
Without a powerful electron-drawing group, nucleophilic aromatic substitution is difficult.
In detail, aromatic substitutions have been studied.
Depending on the reactants, either of two mechanisms may be involved.
One mechanism is similar to the aromatic substitution mechanism, except that nucleophiles and carbanions are not involved.
Benzyne is an interesting and unusual intermediate.
Consider the reaction of 2,4-dinitrochlorobenzene with sodium hydroxide.
A negatively charged sigma complex results when hydroxide attacks the chlorine.
The negative charge is delocalized over the ring's ortho and para carbons.
2,4-dinitrophenol is deprotonated in this basic solution because of the loss of chloride from the sigma complex.
The leaving group gives the product.
The product is acidic and deprotonated by the base.
After the reaction is complete, acid would be added to the phenoxide ion.
The mechanism box shows the resonance forms that show how para to the halogen helps to stable the intermediate.
Formation of the negatively charged sigma complex is unlikely without strong resonance-drawing groups in these positions.
It is not very polarizable and is a poor leaving group.
Strong electron-drawing substituents on the aromatic ring are required for the addition-elimination mechanism.
The reaction takes place in liquid ammonia at -33 degrees.
There is a mechanism different from the one we saw with the addition-elimination of halobenzenes.
bromide ion can be expelled by the carbanion.
The two carbon atoms bonding between them are given additional strength by the overlap of this orbital and filled one.
The overlap of 2 orbitals is not very effective because they are directed away from each other.
Triple bonds are usually linear, but this one is very strained.
Amide ion is a strong nucleophilic, attacking at either end of the triple bond.
The toluidine is given after the subsequent protonsation.
The benzyne mechanism works when the halobenzene is not activated and forcing conditions are used with a strong base.
There is a two-step elimination.
The substituted product is given by a nucleusphilic attack.
When a substitution with a powerful base and without strong electron-drawing groups takes place, the benzyne mechanism should be considered.
Review flashcards and saved quizzes
Getting your flashcards
Privacy & Terms