[noork85]

does this look right?

if not, please point out whats wrong with the mechanism.

https://www.dropbox.com/s/kn2is9cpl41hf96/2013-05-01%2021.11.02.jpg

[betterbesafehero]

I don't think it's right, how come CH₃OH becomes CH₃O^- ?

[noork85]

ok it adds as methanol and not methoxide, but it does lose the H when it bonds to the carbon, because oxygen forms a positive charge.

what else seems wrong???

[TwistedConf]

It's not right at all-- and there are actually so many problems with what you wrote that it's not worth going through it.

Go back and review acid-catalyzed acetal formation reactions and then try it again.

[betterbesafehero]

Try taking 'hemiacetal route', react the alcohol with aldehyde group, it will form an hemiacetal, remove water, attack of carbocation on electron rich site(i.e. the carbon attached with OH), removal of proton, leads to the structure.

If you are not able to understand it properly, I will upload a picture for you..!

[betterbesafehero]

ok it adds as methanol and not methoxide, but it does lose the H when it bonds to the carbon, because oxygen forms a positive charge.

what else seems wrong???

that H goes and stick with O^- to form an hemiacetal..!

and after that the reaction proceeds..!

[noork85]

thanks.....i realize this is material we havent yet covered in my orgo class. i was doing a practice exam of my professors and she tends to recycle her exams, so thats where i got that from. and we havent covered hemiacetal formation yet

[noork85]

Try taking 'hemiacetal route', react the alcohol with aldehyde group, it will form an hemiacetal, remove water, attack of carbocation on electron rich site(i.e. the carbon attached with OH), removal of proton, leads to the structure.

If you are not able to understand it properly, I will upload a picture for you..!

if isnt too much of a problem, can u please upload a picture. thank u

[Dan]

It is standard acid-catalysed acetal formation, no funny business here.

Maybe look up linear vs cyclic forms of sugars, and look up glycosylation for inspiration.

[betterbesafehero]

^^I think I already answered the question...isn't it ?

@noork85: No, not much of problem for me, will upload it in few hours.

[betterbesafehero]

I think that you don't know the mechanism of formation of 'hemiacetal', so first I have shown the mechanism of formation of 'hemiacetal'.

In Step 2:  represents resonating structures, and the one in which C bears the positive charge is more stable.

[Dan]

Right idea, but I think your steps are in the wrong order. Intramolecular reactions are faster than intermolecular reactions.

Please do not give final answers, this is a Forum Rule.

[betterbesafehero]

^^^May I know which steps are in wrong order ?

He already had the answer, I gave him the mechanism. I gave him the hint, he was not able to understand it, it saves time. I gave him the mechanism how hemiacetal forms, which are available on other sites also.

Fine, it won't be repeated again.

[Dan]

^^^May I know which steps are in wrong order ?

I'd swap steps 2 and 6; I think this is an intermediate:

[betterbesafehero]

^^^Yes, I think you are right, but I wanted to show him how hemiacetal really forms. Well, thanks for your keen observation, I also learned something. There are many doubts in intramolecular substitution, you could have easily helped me. Some answers are still pending. I sometimes feel neglected here.

I am a very young student, I am yet to begin my undergraduate studies. I have read many books thoroughly, even multiple times extending it to 6 or 7 times. Whatever is there in the book, I understand it completely. Some topics are not covered in books, my teachers also skipped it.