Organic Questions

[KappaSig]

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1st. question if you have the following complete the product...


H3C-C=O-OC2H5 1)CH3MgCl, 2)H3O+

They say the answer is t-butyl alcohol, i see why its alcohol, i dont get how its t-butyl though...

2nd question is why do we assume there is 2 moles of this reactant:


CH3-CH-C=O-OC2H5 1) NaOC2H5 2) H3O+

it says its a claisen reaction, how do we know that just by looking at this?

the answer is


CH3-CH-C=O-OC2H5
......C=O
......CH2
......CH3

+ C2H5OH

 

[KappaSig]

forgot to mention on the 2nd question the dots below the C don't mean anything it was just put there so you know where it was aligned

 

[molar3]

is this from destroyer? looks familiar.
anyway, i think its because when you have an ester and a grignard, you always assume 2 moles. so for the 1st problem you listed, you add a ch3 and remove the oc2h5 and then since u assume 2 moles with an ester, you add 1 more, to get another ch3, leaving you with t butyl.

 

[molar3]

and its t butyl alcohol because with the grignard youre added h30 so youre protonating the =o into an OH

 

[KappaSig]

I understand why the alcohol is added as you said about the h30..

but how does it give it 2 more ch3's? on the 1st one

 

[riro2]

The rule is when u react an ester with a grignard, the grignard will attack twice. the problem already has 1 ch3. The leaving group will be OR group. So when u attack the ester twice, you will be adding 2 ch3's and kicking out the LG. You are left with a t-butyl.

 

[samdig]

Ya this formula is actually in KBB. Grignard reactions with esters go twice. The first time u get an alcohol, and the second the OH goes away.

 

[jhanago]

I think I can explain the first one..


Okay so we have an ester, correct? As we know, the ester portion (OC2H5) is a good leaving group. Therefore, the CH3- of the grignard will attack the carbonyl and cause the ester to fall off. This leaves..


O
||
c
/ \
CH3 CH3

However, with grignard and esters.. the grignard ALWAYS attacks twice. We can assume two molar equivalents. Usually, they SHOULD notify you of that but they expect you to assume it. The Grignard then attacks the carbonyl but since there is no leaving group, the pi electrons fly up to the O to make...


O-
|
C
/ | \
CH3 Ch3 Ch3


The H30 then protonates the Oxygen to make an alcohol and the finishing product is T Butyl Alcohol

OH
|
C >>>> T BUTYL ALCOHOL
/ | \
CH3 Ch3 Ch3

 

[whatDATmean]

I believe in order to see if its a Claisen condensation it must have a ester group react with an alkoxide (normally OEt) followed by H3O+ to neutralize the base and the enolate since there is a second acidic alpha hydrogen left.

 

[PreDental88]

I believe in order to see if its a Claisen condensation it must have a ester group react with an alkoxide (normally OEt) followed by H3O+ to neutralize the base and the enolate since there is a second acidic alpha hydrogen left.

You'll begin to identify claissen reactions when you start to feel more comfortable with them. But if you reach this problem and have no idea what to do, think of it mechanistically. To add to whatDATmean's post, this is how the mechanism works:

http://commons.wikimedia.org/wiki/File:Claisen_condensation.png