[HaroTaro]

Please help me with this one? Also... did one of the O just disappeared?

[oc dummy]

Since you have an H+, start with protonation and then go from there 

[HaroTaro]

I was thinking that maybe this quetion has something to do with formation of tetrahedral and a group gets kicked off when O reforms double bond. But I can't seemed to get teh O18 right.

[azmanam]

2 things.  O¹⁸ does not scramble.  Can you draw a mechanism?  Second, an ether is not the byproduct.  A mechanism will do wonders here.

http://www.cem.msu.edu/~reusch/VirtTxtJml/crbacid2.htm#react1

[HaroTaro]

Thanks for the link. It's really useful. A quick question,when the methanol attacks the ester, do we have to show how CH3OH changes into CH3O-? Do we use a base B- to remove it?

[azmanam]

no negative charges in an acid catalyzed mechanism...

[HaroTaro]

that's what I thought... but then how do you remove the H? since you're attaching OCH3 to the ester to kick off the other group?

[macman104]

Thanks for the link. It's really useful. A quick question,when the methanol attacks the ester, do we have to show how CH3OH changes into CH3O-? Do we use a base B- to remove it?

http://www.mhhe.com/physsci/chemistry/carey/student/olc/ch20reactionsesters.html Look at the mechanism for the Acid Catalyzed Hydrolysis of Esters.  Except, where you see H-OH, replace it with CH₃-OH

Transesterification (the act of replacing one alkyl group for the ester with another) is just a form of hydrolysis where the attacking OH is an alcohol and not water.

[HaroTaro]

wow~ completely understood! THANKS EVERYONE!!!

[oc dummy]

i just reawlized its tertiary carbon.. so wouldn't that involve a SN1 reaction or something?

[macman104]

You mean for the ester?  Follow the link here, to look at the special case of t-butyl ester cleavage.  It follows a slightly different mechanism for the exact reason that it is tertiary and forms a stable carbocation.

http://www.cem.msu.edu/~reusch/VirtTxtJml/suppmnt4.htm#top1

[oc dummy]

hmm thaanks! I understand that part, but i'm trying to get the other product (the ester)

Does the methanol attack the carbonyl center, and then a leaving group leaves? but which one? because theres OH and O-

Would I add a H+ on the OH to make it H20 so it leaves?
Thanks.