[arvind1990]

   Hi,


What is the product formed when C6H6(benzene) reacts with CH3CH2CH2Cl.
Is it cumene or 3-phenylpropane

[letk0]

It's cumene. A hydride shift occurs to form a more stable carbocation.

[arvind1990]

What do you mean by hydride shift. Can you explain me please..

[victor]

in order to make a more stable carbocation, there's a shift of H atom to convert from propyl cation into isopropyl cation (more stable).

[Dan]

Side note: Carbocation rearrangement in the Friedel-Craft's alkylation is one of the main problems with it - if the rearrangement is not desireable. If you wanted to make 3-phenylpropane (which is a common question on first year organic chemistry exam papers) you could use Friedel-Crafts acylation, followed by reduction of the carbonyl, this would avoid rearrangement.

[latent_lamp]

Isopropyl benzene is major product under certain conditions (i.e. excess benzene), expect poly substituted benzenes.

[victor]

Umm...can I use addition with Grignard reagent??
so, benzene + propylmagnesium bromide =>

the only products that I think, it will form Phenylmagnesium bromide and propane..is it true??

[Dan]

Umm...can I use addition with Grignard reagent??
so, benzene + propylmagnesium bromide =>

the only products that I think, it will form Phenylmagnesium bromide and propane..is it true??

You certainly won't get addition to benzene with a grignard. I don't think there will be any reaction

[victor]

Whoa...I think that it woul react since the formation of carbanion also creates Mg++Br- which I consider that as electrophilic group..

[Dan]

Whoa...I think that it woul react since the formation of carbanion also creates Mg++Br- which I consider that as electrophilic group..

Mg²⁺ surely? Actually, I think free Pr^- might be basic enough to deprotonate benzene, so you could be right, PrMgBr + PhH ----> PhMgBr + PrH. But the Pr^- is unlikely to be a free anion, so I have doubts. This would not be electrophilic aromatic substitution, it would be an acid/base reaction.

[victor]

Oh...I got the wrong reaction name then..
But, I think that deprotonation of H atom in benzene I think is prohibited since if that thing is done, it will results in phenyl cation which is not allowed by benzene ring because of its sp orbital (others are sp2 orbitals).
so? no reaction? or electrophilic substitution? or other reaction?

[movies]

It's not a phenyl cation, it's a phenyl anion.  It's not really as bad as you think.

And the orbital with the anion is sp<sup>2[/sub], the orbitals of the aromatic system are just p; there are no sp orbitals in benzene.

By the way, the pKa of propane is around 44 and the pKa of benzene is around 35, so the deprotonation that Dan mentioned will surely occur.</sup>