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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: lrisNil on March 06, 2015, 03:35:15 AM

Title: Breaking Open A Ring
Post by: lrisNil on March 06, 2015, 03:35:15 AM

 :spinup: >:( :spindown:                         :spinup: :) :spindown:

I'm a little stuck on this mechanism.
I believe the first step is to open the ring and create a double bond.
Is there any fast way to know which electrons will do a nucleophilic attack?

Thank you for reading this~! (picture attached)

Title: Re: Breaking Open A Ring
Post by: discodermolide on March 06, 2015, 04:02:12 AM

Think about the sugar, is it always in the cyclic form or can you influence the system to do other things?
Also think about retro-aldol reactions.

Title: Re: Breaking Open A Ring
Post by: lrisNil on March 06, 2015, 07:08:52 PM

Thank you for answering Discoder,

I broke an O-H bond and gave the electrons to the O.
This leads to a series of electron pushing,

when the electrons reach the O in the top center of the molecule,

I threw them onto a random H2O, and this Opened the Ring

Is this correct?

Thank you for reading this

Title: Re: Breaking Open A Ring
Post by: discodermolide on March 06, 2015, 11:06:12 PM

Yes, and an interesting description. So you now have the open form of the fructose.
What next?

Title: Re: Breaking Open A Ring
Post by: lrisNil on March 06, 2015, 11:52:07 PM

Thank you for confirming that this is correct!
By the way, should I write reverse arrows for the steps so far? 
Since I just pushed electrons so far, are these structures resonance?  :resonance:

Anyway, next I rearranged the molecule into vertical shape instead of a ring.
It contains one C=O bond.

I *think* the water can attack that carbon .. then the C=O would become C-OH, but I'm not completely sure >.<
 

Title: Re: Breaking Open A Ring
Post by: discodermolide on March 07, 2015, 03:56:31 AM

It would help you and me if you actually drew the reactions out, with arrows. You can post them here for all to see and comment upon.

Title: Re: Breaking Open A Ring
Post by: lrisNil on March 07, 2015, 05:19:25 AM

Here it is! i hope it's visible  :D 

Title: Re: Breaking Open A Ring
Post by: discodermolide on March 07, 2015, 08:30:49 AM

OK, now what about the next part?

Title: Re: Breaking Open A Ring
Post by: lrisNil on March 07, 2015, 07:51:11 PM

Before attempt to continue, I was wondering does it make sense that the electrons on the H went to the O out of no where? i was thinking of putting a reversible arrow but I'm not completely sure


And for the next step I think I should attack the carbon in the C=O with electrons because it happens so often I just resort to doing that all the time .. hahah  :P 

Title: Re: Breaking Open A Ring
Post by: discodermolide on March 07, 2015, 08:39:02 PM

You have water as a solvent.
Look at the two fragments and see if you can relate them to the open form.
Try drawing some reaction schemes.

Title: Re: Breaking Open A Ring
Post by: lrisNil on March 08, 2015, 07:32:05 PM

Yes! water is the solvent, but I looked it up and water is a bad nucleophile..
is this next step correct?  :-\


Also, Can I use water to do attacks over and over again?

Title: Re: Breaking Open A Ring
Post by: discodermolide on March 08, 2015, 11:08:24 PM

No it's not correct. Look at the two products in your first post. They result from a retro Aldol reaction.
So Google that and see what you can learn there.

Title: Re: Breaking Open A Ring
Post by: lrisNil on March 09, 2015, 02:12:13 AM

Thank you for pointing out my mistake,
After some extensive Googling on retro aldol reactions I came up with this

Title: Re: Breaking Open A Ring
Post by: discodermolide on March 09, 2015, 07:07:52 AM

Yes,in principle, but you should really draw in all the carbon atoms.
So give it another try drawing all the atoms.