Hello, I have a few doubts in organic chemistry.

1. Can the Friedel-Crafts reactions be used for any substituted aromatic ring, where the substituent is a meta-directing group? In other words, is there any meta-directing group that is present in the aromatic ring, and the compound be able to undergo electrophilic substitution at the ring?

2. Does the Friedel-Crafts reaction work for phenols? Can you provide me with a list of groups that when present in the aromatic ring, the compound may not be able to undergo Friedel-Crafts reactions?

3. Please give me a comparison between the Resonance and Inductive effects. When will resonance effect dominate, when will inductive effect dominate, if both are present?

4. Is the phenyl group like the halide group, that is, ortho-para directing by resonance effect and electron withdrawing by inductive effect? Is the phenyl group activating or deactivating?

5. Why is phenyl cation less stable than vinyl cation?

6. What do you mean by 'Complete Delocalisation of Electrons', a neccesity for aromaticity by Huckel's rule? Is it possible to judge from the structure of a compound whether complete delocalisation of electrons is available or not?

7. Why is fluorobenzene the least deactivating among the halobenzenes?

8. Why is pyridine aromatic? Aren't there 8 pi-electrons, violating Huckel's rule?

9. Why is it that a strong lewis acid favours rearrangement over weak lweis acids, in Friedel-Crafts alkylations?

10. Is there a reaction, or a systhesis, that enables us to 'de-alkylate a ring'? That is, for example, produce benzene from an alkylated benzene?

11. Why is toluene more activated as compared to 2-methyl 2-phenyl propane? Isn't the latter more electron releasing, and hence more activating?

12. Why is monobromination of aromatic ring observed when the ring is treated with Br₂ in presense of CS₂?

A quick reply is highly appreciated. Thanks.

1- Yes I think the reaction wud occur. If a meta-directing group is present, the electrophilic subsitution wud occur at Meta position.

2- NO.

In Friedel Craft alkylation and acylation on phenol, we get a mixture of ortho and para substituted product but the yield is bad as a lewis acid-base reaction occurs between -OH and AlCl₃.

3- Very long topic.  But some general points are-

(i) Resonance effect> Hypernojugation > Inductive

(ii) See inductive effect for sigma bonds and resonance effect for pi bonds.

(iii) For halogens, Inductive(-I) effect >> Resonance (+R) effect.

(iv) In benzyne mechanism, to determine the position of incoming group, see the inductive effect of group present on ring as the third additional bond in benzyne is Sigma bond and NOT pi.

4- Phenyl group shows -I effect. As far as its resonance effect is concerned, I am a bit confused abt it so wont answer it.

5- Not sure but maybe becoz unsaturation is more in benzene ring than in a single double bond. And by putting a positive charge, u r increasing that unsaturation that's why.

6- In figure.

7- Electron density is highest on F as compared to all the halogens. So its +R wud be more dominating as compared to other halogens.

8- There are 8 pi electrons for sure BUT only 6 electrons are involved in conjugation. The lone pair on N is not involved in conjugation as it is not in the plane of the pi electron clouds on benzene ring.

9- Strong lewis acids form proper carbocations and proper carbocations always prefer rearrangement whereas in case of weak lewis acids, improper carbocation is formed i.e., a delta positive charge on C and an improper carbocation doesnt undergo rearrangement.