[noor123]

Hey all,

i have attached a pic. of the structure. Now i know the mechanism for the reaction and what the products become. But i have a question about a step in the reaction.

Once the double bond attacks on the Cl and it forms a bridge, then the OH- comes and attacks on the carbon that is attached to the phenyl group. Why does it do that? why not the other carbon that also was  as a double bond initially?  I mean both of the carbons are equally 'substituted' in accordance to markovnikov....right?


Also, a question not necessarily related to this problem, but how do i decide which of the atoms are wedges and which are dashes? Like say i have been given the same problem as attached, and i have to give the products with their proper structures (wedges/dashes). How do i do that when it is not given in the problem itself how it looks initially?

[discodermolide]

Compare the stabilisation of the two possible carbocations that can be produced by opening of the chloronium species.
As to the stereochemistry: think about the steric factors in the two possible "intermediates" and also remember that on opening of the chloronium species yiu have a single C-C bond which can rotate.

[noor123]

So you mean the phenyl group,, it donates electrons right? does this make that carbon more stable?

And im still not sure about the stereochem. part 

[discodermolide]

You need to draw out the resonance structures for the two carbonium ions. The benzylic is more stable than the secondary.
You start with a trans alkene, so when the C=C is broken the remaining C-C bond will rotate into a position where the steric interactions between the substituents are minimised.

[AromaticAcrobatic]

"I mean both of the carbons are equally 'substituted' in accordance to markovnikov....right?"

Think about hyperconjugation and then think about the stability of the markovnikov and anti-markovnikov products. Why are they stable? Then apply this reasoning to your molecule.

[Enthalpy]

[...]both of the carbons are equally 'substituted' in accordance to markovnikov....right?

I read in an other book and in
Krishna's Advanced Organic Chemistry, Volume 1
that a phenyl isn't like a methyl for Markovnikov, I quote:
"The order of carbocation stability it tertiary ~ benzylic > allylic ~ secondary > primary ~ vinylic > Phenyl"
please consider I have no opinion about this, just pasting what I've read.

[AdiDex]

I think alylic carbocation is more stable than benzylic carbocation..
And they are almost equally stable..

[discodermolide]

I think that benzylic are more stable than allylic.

[zsinger]

Disco is correct.  Benzylic have more resonance opportunities.
       -Zack

[AdiDex]

Ahhmmm ahhmmm..

Let me put my view..

Imagine your favourite activities are playing Video games(Most Favourite) ,

and other-one Reading Chemistry , spending time in a chemical lab . ( these two are activities are those activities in between you can't choose one that which one you want to do , or say you like them equally.)

You dislikes - Reading history , reading civics , reading economics

Suppose two cases -
Case 1.
    You have Four rooms in your house containing these things , stuff are as follow -
    1. Video games 2. History books  3. Civics books  4. Economics       books

I don't think you are going to spend your so much time in room no. 2 ,3 and 4 .
So The contribution of  Room 1 in your life is pretty high ....you are going to live your life in living in room 1.

This the case of Benzylic carbocation
Room no. 1 is the canonical structure containing aromatic ring.

Case No. 2

You have two rooms containing these things -

1. Chemistry books  2. Chemical Lab

So in this case you are going to spend your time in both of the room. Equally ...

This is the case of allylic carbocation..
All rooms are equivalent , i.e similar (or say identical )resonatic structure brings more stabilty to the system .

That why both (benzylic and allylic) have similar stability order..….

Note : only no. Of resonatic structure don't decides the stability..

[noor123]

ooh nice!  like the way you put it

[AdiDex]

Thanks buddy..