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Topic: Propanal with Methanol and HCl  (Read 18368 times)

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Offline Aznhmonglor

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Propanal with Methanol and HCl
« on: March 07, 2009, 06:30:00 PM »
Structure of the dominant product formed by treating propanal with methanol containing dissolved HCl?


So I know what propanal looks like, added with HCl does it look like this?


Now that structure with methanol looks like this right? and should be my final answer?

Offline James Newby

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Re: Propanal with Methanol and HCl
« Reply #1 on: March 07, 2009, 06:34:43 PM »
the HCl is a catalyst, MeOH is a much better Nucleophile than Cl-. The acid protonates the aldehyde and MeOH attacks the carbon of the carbonyl.  Can you draw the resulting product and tell us the functional group made??
4th year undergraduate at the University of Sheffield

Offline Aznhmonglor

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Re: Propanal with Methanol and HCl
« Reply #2 on: March 07, 2009, 07:07:11 PM »
the HCl is a catalyst, MeOH is a much better Nucleophile than Cl-. The acid protonates the aldehyde and MeOH attacks the carbon of the carbonyl.  Can you draw the resulting product and tell us the functional group made??

hmmm is the functional group made an ester?

Offline James Newby

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Re: Propanal with Methanol and HCl
« Reply #3 on: March 07, 2009, 07:22:06 PM »
close! If the MeOH attacks the carbonyl to form the tetrahedral intermediate, it cannot reform the carbonyl as there arent any good leaving groups (maybe the MeOH but that goes back to starting materials).

If you were to run the reaction in an NMR machine you would see a spectra of both products

The new functional group is a hemiacetal.
4th year undergraduate at the University of Sheffield

Offline Aznhmonglor

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Re: Propanal with Methanol and HCl
« Reply #4 on: March 07, 2009, 07:34:31 PM »
Hey that helps alot so it should look like this right because I drew a hemiacetal.


Offline James Newby

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Re: Propanal with Methanol and HCl
« Reply #5 on: March 07, 2009, 08:04:14 PM »
That right, i tried to insert a picture but still cant do it!!  It would form an ester if the aldehyde was a carboxylic acid ie propanoic acid.  If you want some further insight into hemiacetals and acetals look in Clayden Organic chemistry pg 340.

Im happy to answer any other questions you have on this subject as its one i studied last year.
4th year undergraduate at the University of Sheffield

Offline macman104

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Re: Propanal with Methanol and HCl
« Reply #6 on: March 07, 2009, 09:21:20 PM »
James, when you make a post, there is the link that says "Additional Options...", click that, and you can attach a file.

Offline James Newby

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Re: Propanal with Methanol and HCl
« Reply #7 on: March 08, 2009, 10:51:58 AM »
i see it now, sorry! One day ill understand these fancy computer things ;)
4th year undergraduate at the University of Sheffield

Offline nj_bartel

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Re: Propanal with Methanol and HCl
« Reply #8 on: March 08, 2009, 11:43:50 AM »
While hemiacetal is technically correct, I think it should be noted that hemiacetals are unstable, and that's going to go on to react to form an acetal.

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