Question:which one of the following benzene derivatives can undergo Friedel Crafts acylation upon treatment with benzoyl chloride and aluminum chloride? a) benzenesulfonic acid, PhSO3H b)benzonitrile, PhCN c) trifluorotoluene, PhCF3 d) trichlorotoluene, PhCCl3 e) fluorobenzene, PhF explanation please, thanx

Answers:You need an electron DONATING subsitutent on the benzene ring to promote the reaction. SO3H, CN, CF3, and CCl3 are all withdrawing. F can do either depending on what's necessary. So, PhF is the correct choice.

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Question:When performing a Friedel-Crafts alkylation reaction, not only does one have the problems of multiple alkylation and rearrangement of the cation, but the presence of strong electron donating groups prevents reaction. Provide an explanation for this.

Answers:strong electron donating groups on the benzene ring will be attacked by the lewis acid and form a complex which will deactivate the lewis acid and the benzene ring because of the cation that they form.. MeO-Ph + AlCl3 ---> Me(Ph)O-AlCL3- H2NPh + BCl3 ---> H2N(BCl3)Ph-

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Question:A Friedel-Crafts acylation reaction between toluene and acetyl chloride produces 4-methyl acetophenone; whereas, the reaction between benzaldehyde and acetylchloride produces 3-acetyl-benzenecarbaldehyde. Fully explain these reactions.

Answers:The reason for the difference in position of where the acetyl group attaches is due to the group already substituted onto the benzene ring. Both the reactions are electrophilic substitution reactions, but as the benzene ring already has something attached to it, you have the problem of where the incoming group will attach. The group that is already attached is classified as either activating or deactivating towards the aromatic ring, where activating groups tend to stabilise the intermediate by donating electrons into the ring, whilst deactivating groups draw electron density out of the ring. In the first example, the methyl group of toluene is activating and donates electron density into the ring. However the electron density is not equally distributed throughout the ring but is concentrated on atoms, 2, 4, and 6 (ortho/para). These regions are therefore most reactive towards an electron poor electrophile (as there is now a higher electron density here). Generally the highest electron density is at the ortho (2 position), but in this case, the acetyl group goes to the para (4 position due to steric effects. In the case of benzaldehyde, the opposite is happening. Electron density is pulled out of the ring structure. Again, the ortho/para positions are most effected and more electron density is withdrawn from them. THis therefore leaves more electron density around the meta (3 position) and so the incoming, electron poor, group is directed here as that is where there is the highest electron density. The result: with toluene, the acetylation occurs at position 4, and with benzaldehyde it happens at position 3 giving you: 4-methyl acetophenone and 3-acetyl-benzenecarbaldehyde respectively.

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Question:Would the Friedel-Crafts acylation of fluorobenzene with acetyl chloride and aluminum chloride occur faster or slower than the acylation of benzene... and would it produce mostly o- and p- fluoroacetophenone or mostly m-fluoroacetophenone?

Answers:For the first part of the question, the acylation of fluorobenzene is slower than the acylation of benzene. This is because the fluoro- group is a weakly deactivating group. A deactivating group withdraws the electrons from the benzene ring, reducing its electron density. Thus, the benzene ring is less negatively charged. It is then less susceptible to an attack by electrophiles (electron-loving species), and less likely to occur compared to the chances of an electrophilic attack on benzene.

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