Naughty Grignard rxn ?

[student1982]

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Please explain the logic of grinard reagent attacking OH in these 2 examples

1)3-hydroxycyclohexanone with CH3MgI --> 3-hydroxycyclohexanone
I thought grinard always aim for the c=o functional group, the book shows it attacked the OH group but then the methyl group falls off, & then followed by addition of an H

2) hydroxycyclooctane + Ch3Ch2MgBr -->
The answer shows that the grinard attack the OH group also


3rd question
cyclohexanol + LiAlHr/TiCl4 --> cyclohexane
whats the role of TiCl4

4th question
Why would a dihalide such Br-Br be electrophylic & gets attacked by pi bond of an alkene?

thanks for any replies

 

[REH]

)3-hydroxycyclohexanone with CH3MgI --> 3-hydroxycyclohexanone
I thought grinard always aim for the c=o functional group, the book shows it attacked the OH group but then the methyl group falls off, & then followed by addition of an H

--Grignard reagents will attack an acidic hydrogen if there's one present. In this case, the -OH group has an acidic hydrogen. This behavior is the reason why you wouldn't want to use a solvent like water with a Grignard. The acidic hydrogens of water would neutralize the Grignard reagent.


2) hydroxycyclooctane + Ch3Ch2MgBr -->
The answer shows that the grinard attack the OH group also

--The response to the first question explains why in this reaction, the Grignard reagent attacks the carbonyl carbon.


3rd question
cyclohexanol + LiAlHr/TiCl4 --> cyclohexane
whats the role of TiCl4

I have no clue about this one...Sorry

4th question
Why would a dihalide such Br-Br be electrophylic & gets attacked by pi bond of an alkene?

Well, let's think about it for a minute...What is does an alkene have? pi bonds right? There is a concentration of negative charge between the two carbon atoms with pi orbitals extending above and below the plane of the sigma bond. This makes them act as nucleophiles. Br-Br is a larger diatomic molecule and its polarizable. This allows it to behave as an electrophile. Nucleophiles attack electrophiles, and so we see a reaction. Hope this helps.

REH.