Anothe orgo question!

[atlanta213]

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Cyclohexanol 1) CH3Li, Et2O ------> ?
2) H30+

What will be the product?

 

[Maygyver]

Will it just be cyclohexanol with a methyl group attached at the same place?

 

[rdhdds1]

Will it just be cyclohexanol with a methyl group attached at the same place?

I believe you are right. I just did it and got cyclohexane with the methyl attached at the location of the OH.

Anyone else?

 

[atlanta213]

you guys are right. how did you know methyl group would be on the location of OH?

 

[osimsDDS]

Yea thats what i got....

Can someone go over the mechanism for this, its organometallic correct?? thus it acts as a base like a greignard reaction...

However i never understood the mechanism with organometallics..thanks

 

[Maygyver]

you guys are right. how did you know methyl group would be on the location of OH?

This is a Grignard reaction I believe. But anyway, look at the carbon that the oxygen is connected too. It has a partial positive charge and the methyl group will have a negative charge (CH3-LI+). Negative attacks positive. 😉 Hope it helps.

 

[Maygyver]

Yea thats what i got....

Can someone go over the mechanism for this, its organometallic correct?? thus it acts as a base like a greignard reaction...

However i never understood the mechanism with organometallics..thanks

Does my explanation help? I can go into more if you need.

 

[osimsDDS]

Does the H3O+ react with the alcohol group and dehydrate it while forming OH at the same place...

 

[rdhdds1]

you guys are right. how did you know methyl group would be on the location of OH?

Okay I am not at all the ochem guru. I actually did well in my classes but have no idea how.

This is how I remember to do this one. I never could remember grinard and all that jazz. What I look at is who is attacking who?

Li wants the H and Et20 kills oxygen at the bond. This leaves a lonely CH3 to suck his/her thumb until it is added to the ring.

That is how I did it. Maybe wrong in theory and application but I got the answer

 

[atlanta213]

What is the role of Et20 in here?

 

[Maygyver]

What is the role of Et20 in here?

Solvent.

 

[rdhdds1]

Solvent.

Beat me to it😀

 

[AndyK]

Hold on, if you have an alcohol (pKa=16, but for this it's probably around 12) and a carbanion (pKa=25), won't the carbanion just abstract the proton from the alcohol and become methane?

Remember when you did grignard in lab and you had to make sure everything was totally dry or else you'd get messy results?

BTW rdhdds1, the Li can't want the H. It's more than happy in its cation form, so it would make no sense for it to form a covalent bond or any other kind of bond other than ionic. Octet rule...

CH3Li is an ionically bonded molecule: [H3C:]- anions and Li+ cations

So my answer is that the result is CH4 and cyclohexanol

 

[IDoWhatIWant]

Okay I am not at all the ochem guru. I actually did well in my classes but have no idea how.

This is how I remember to do this one. I never could remember grinard and all that jazz. What I look at is who is attacking who?

Li wants the H and Et20 kills oxygen at the bond. This leaves a lonely CH3 to suck his/her thumb until it is added to the ring.

That is how I did it. Maybe wrong in theory and application but I got the answer

Why would Li want a hydrogen? Li is an alkali metal, which would want something with a negative charge, i.e. -OH. But the DAT doesn't ask for mechanisms, so good job.

 

[IDoWhatIWant]

Hold on, if you have an alcohol (pKa=16, but for this it's probably around 12) and a carbanion (pKa=25), won't the carbanion just abstract the proton from the alcohol and become methane?

Remember when you did grignard in lab and you had to make sure everything was totally dry or else you'd get messy results?

BTW rdhdds1, the Li can't want the H. It's more than happy in its cation form, so it would make no sense for it to form a covalent bond or any other kind of bond other than ionic. Octet rule...

CH3Li is an ionically bonded molecule: [H3C:]- anions and Li+ cations

So my answer is that the result is CH4 and cyclohexanol

Please correct me if I'm wrong since I suck at Ochem, but isn't it required to keep things dry to synthesize a Grignard reagent? I've seen reactions with water as the solvent.

 

[drgreen]

Hold on, if you have an alcohol (pKa=16, but for this it's probably around 12) and a carbanion (pKa=25), won't the carbanion just abstract the proton from the alcohol and become methane?

Remember when you did grignard in lab and you had to make sure everything was totally dry or else you'd get messy results?

BTW rdhdds1, the Li can't want the H. It's more than happy in its cation form, so it would make no sense for it to form a covalent bond or any other kind of bond other than ionic. Octet rule...

CH3Li is an ionically bonded molecule: [H3C:]- anions and Li+ cations

So my answer is that the result is CH4 and cyclohexanol

You rock, and are dead on! the grignard is a powerful base and all it does is deprotonate the alcohol. theres no partial positive charge on the hydroxyl carbon, i have no idea where that idea came from. after we form an O-, adding H+ just protonates once more to form cyclohexanol once more.

and p.s. not only is there nowhere for the grignard to attack the cyclohexan, but there IS NO GRIGNARD anymore, it was ruined by the proton (became CH4).

 

[futuredent22]

The product will be the very same cyclohexanol that you started with. Organometallics are very strong bases and will immediately react with water and alcohol (both with similar pKa's). This is why when you use organometallics, you have to be sure you do not allow it to interact with the water vapor in air (think back to orgo lab when you had to use super-dried test tubes).

In the OP's reaction, the organometallic will take the most acidic hydrogen, which is the alcohol's. Subsequent reaction with H30+ will re-protonate the alcohol back to cyclohexanol.

 

[Maygyver]

Yeah, I guess it was too late to think last night lol. The answer I got would occure if the alcohol was a ketone.

 

[osimsDDS]

THIS IS EXACTLY what i was thinking last night, i was gonna post it but i figured that others were correct and i was not haha...

It's just that organometallic reagents are very strong bases such as greignards and basically deprotonate the alcohol...however, you have an acid after (H3O+) that protonates the O-