Destroyer 97 help :p

[NuckingFutz]

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Can someone explain to me where the 4th CH3 came from??

Can I also assume that O-C2H5 is a good leaving group? I figured that the methyl group came from the CH3MgCl, but why did it add twice to form a t-butyl alcohol??

Thanks 😳

 

[TeamGuo]

Can someone explain to me where the 4th CH3 came from??

Can I also assume that O-C2H5 is a good leaving group? I figured that the methyl group came from the CH3MgCl, but why did it add twice to form a t-butyl alcohol??

Thanks 😳

OC2H5 being next to a carbonyl makes an ester. Esters are decent leaving groups, when you protonate that O it becomes a great leaving group. But in this case, since the incoming nucleophile is so damn strong it doesn't really matter. Grignard will ALWAYS attack twice to a carbonyl unless it's stated 1 equivalence of it.

Hence, that's why you get the t-butyl alcohol. O- is just protonated by the acid work up in the end.

 

[klutzy1987]

OC2H5 being next to a carbonyl makes an ester. Esters are decent leaving groups, when you protonate that O it becomes a great leaving group. But in this case, since the incoming nucleophile is so damn strong it doesn't really matter. Grignard will ALWAYS attack twice to a carbonyl unless it's stated 1 equivalence of it.

Hence, that's why you get the t-butyl alcohol. O- is just protonated by the acid work up in the end.

Sort of Correct. Only Esters will undergo grignard twice. The reason for this is that after the first grignard you get a ketone. However Ketones are very reactive with grignards and therefore it will not be able to stop after the first alkylation and will go to a second alkylation and the ketone will be turned into a tertiary alcohol.

A regular carbonyl like an aldehyde or ketone will only underfo one round of alkylation.

 

[drgreen]

1)CH3- attacks carbony, kicks up electrons onto Oxygen
2)electrons from oxygen come down to reform carbonyl, kicking off -OC2H5
3)another CH3- attacks the carbonyl, kicks up electrons onto oxygen
4)Electrons dont come back down because CH3 is a BAD leaving group
5) we add acid to protonate the O-, forming a t-butyl alcohol

 

[jdent]

Ester is 2 mol of gringard- very important to have on tips of fingers. The OC2H5 is the leaving group.

 

[TeamGuo]

Sort of Correct. Only Esters will undergo grignard twice. The reason for this is that after the first grignard you get a ketone. However Ketones are very reactive with grignards and therefore it will not be able to stop after the first alkylation and will go to a second alkylation and the ketone will be turned into a tertiary alcohol.

A regular carbonyl like an aldehyde or ketone will only underfo one round of alkylation.

Yea but with ketones you can still attack twice. When you attack once, you form an hemiacetal but you can get an acetal with ketones by attacking twice. Hydroxyl group can be turned into a water and leave for substitution.

But you are right about not all carbonyls will react twice with grignard.

 

[klutzy1987]

Yea but with ketones you can still attack twice. When you attack once, you form an hemiacetal but you can get an acetal with ketones by attacking twice. Hydroxyl group can be turned into a water and leave for substitution.

But you are right about not all carbonyls will react twice with grignard.

Incorrect if you are talking about grignard. A grignard will only react with a ketone once. What you are referring to is OCH2CH3 which will react like that. A grignard will only make a trertiary alcohol when reacted with ketones.