[ritwik06]

Find out the outcome of the following reaction:
Benzene+ Cl-CH₂-CH₂-CH₂-F + BCl₃(Catalyst) -------->

My attempt at an answer:
Since BCl₃ is a hard acid, it will react with the -F end (harder end) of the alkyl halide, forming the following carbocation:

Cl-CH₂-CH₂-CH₂⁺

This carbocation will rearrange to a more stabler carbocation.
Cl-CH₂-CH⁺-CH₃
which would in turn attack on benzene ring
forming:
Cl-CH₂-CH(Ph)-CH₃

Am I right??
If I am not, please point out my mistakes at each wrong step. I shall be very grateful.
regards,
Ritwik

[alphahydroxy]

OK, this is a Friedel-Crafts reaction. Essentially, I think you have the right idea, but the wrong outcome.

I would assume (and I may be wrong) that the chrloride would be the atom to interact with the catalyst in preference to the fluoride - probably because of the higher availbility of the lone pair, and the relative weakness of the C-Cl bond.

The rearrangement part is correct, though I think you may end up with a mixture of products.

[ritwik06]

I would assume (and I may be wrong) that the chloride would be the atom to interact with the catalyst in preference to the fluoride - probably because of the higher availability of the lone pair, and the relative weakness of the C-Cl bond.

First of all thanks for the help.
Oh, I see that viewpoint. It might seem convincing but someone please help me deduce this through hard soft acid base concept- if its not a problem for you.

The rearrangement part is correct, though I think you may end up with a mixture of products.

Oh, yes, thats always the case! I get a mixture of products.
But I need to specify the major of the two. Please someone help me further.

Thanks once again.
regards.

[ritwik06]

Have I put forward a question, which cannot be answered logically, or what? I mean, is there no way to guess the products?
I am looking forward to more replies since alphahydroxy was not sure about it.
Please *delete me*!

[sjb]

If you're talking hard and soft, then I think the fluoro substituted products are more likely than the the chloro ones, as the polarisability of the B-Cl bond is similar to that of the C-Cl, imo. I'd also think that the branched chain would be more stable than the linear one, so 1-fluoro-2-methyl ethylbenzene would be the most likely product.


But it may be that you actually have to do the experiment to really get a better handle on what's going on.