[Aznhmonglor]

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?

[James Newby]

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??

[Aznhmonglor]

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?

[James Newby]

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.

[Aznhmonglor]

Hey that helps alot so it should look like this right because I drew a hemiacetal.

[James Newby]

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.

[macman104]

James, when you make a post, there is the link that says "Additional Options...", click that, and you can attach a file.

[James Newby]

i see it now, sorry! One day ill understand these fancy computer things

[nj_bartel]

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.