[a confused chiral girl]

Hi my fellows~

I think I have some misinterpretation of this question, as I have been attempting them many times but still incorrect. Can someone please show me how to do this..I have included what I did below..

Question: Draw structural formulas for an aldehyde or ketone and alkyl (or aryl) bromide that could be used in a Grignard synthesis of the alcohol shown.


thank you 

[Dolphinsiu]

yes, well done! But I remember my book has told one more possibility!
       
       O
       ll
Ph - C - CH3 + Ph-MgBr

However, would you tell me which reaction is faster when compared with

      O
       ll
Ph - C - Ph + CH3MgBr ?

Make sure you should know the reaction is done without water, otherwise poisioning the Grignard reagent!

H -- O -- H
       ..
     RMgBr
       ..
H -- O -- H

[kiwi]

and if it doesn't have to be an aldehyde/ketone, ethyl acetate (or any acetate really) + 2 eq PhMgBr -> same product

[a confused chiral girl]

yes, well done! But I remember my book has told one more possibility!
       
       O
       ll
Ph - C - CH3 + Ph-MgBr

However, would you tell me which reaction is faster when compared with

      O
       ll
Ph - C - Ph + CH3MgBr ?

thank you for your confirmation as well as another possibilty. I thought about it, and I think my way is faster  ..because the alternate method has Ph-MgBR, and Ph is a ring which is much bigger than CH3, so for that to attack the nucleophile, it would take longer time because of steric hindrance!

[Dolphinsiu]

Yes. You are right

[InPhaseTransit]

Your synthesis is alright but there's something I'd like to add -

thank you for your confirmation as well as another possibilty. I thought about it, and I think my way is faster 

That's correct, alkylmagnesium grignard are more reactive than arylmagnesium.

..because the alternate method has Ph-MgBR, and Ph is a ring which is much bigger than CH3, so for that to attack the nucleophile, it would take longer time because of steric hindrance!

Alkylmagnesium grignard are more reactive for a different reason than steric hindrance of arylmagnesium grignard though. 

Of Mg atom and the Ph group, Mg is more electropositive. Now you put 'delta charges' for the alkyl-metal bond and see what becomes 'positive' and which one 'negative', in order that we see how the probable mechanism works.

Let's do the same for the carbonyl group C=O of the ketone. Put the partial positive and negative charges correctly.

Does the Ph-Mg bond seem likely to break in order that Ph becomes an electrophile to attack the nucleophilic centre of carbonyl group OR does it seem more probable that the more electropositive Mg might somewhat coordinate bond to the more electronegative of C and O in C=O?

To answer now why arylmagnesium are less reactive - because the aryl group is more stable than alkyl - does aromatic stabilisation sound plausible? Delocalisation of the charge you're going to put on the Ph group in the grignard?

[Wisemanleo]

Or to put it simply: resonance. The phenyl groups are resonating with the carbonyl group. More resonance will result in greater stability, and thus less reactivity.