orgoman22

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Does anyone know why nitrogen gets the lone pair instead of oxygen? I thought oxygen was more electronegative.
Look closely at the first step.....we have a NUCLEOPHILE. A nucleophile needs to attack an ELECTROPHILE. The carbonyl group is a perfect position. As you can see, the attack allowed the alcohol to add on. This was simply followed by a proton transfer to finish the job. The reaction continues in the same fashion to the opposite side.

I hope this helps.....

Dr. Romano
 

510586

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Look closely at the first step.....we have a NUCLEOPHILE. A nucleophile needs to attack an ELECTROPHILE. The carbonyl group is a perfect position. As you can see, the attack allowed the alcohol to add on. This was simply followed by a proton transfer to finish the job. The reaction continues in the same fashion to the opposite side.

I hope this helps.....

Dr. Romano
I understand that the carbonyl group is good to attack, but I'm curious as to why the double bonded electron doesn't go to oxygen (more EN) instead of nitrogen
 
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orgoman22

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I understand that the carbonyl group is good to attack, but I'm curious as to why the double bonded electron doesn't go to oxygen (more EN) instead of nitrogen
How could it ? O already has an octet......draw them in to start with, and this should be very very clear. The electrons can move toward the N and maintain the octet.
 

510586

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How could it ? O already has an octet......draw them in to start with, and this should be very very clear. The electrons can move toward the N and maintain the octet.
If the electrons go from the double bond to O, it would be a single bond and 3 lone pairs right? I'm not sure how that breaks the octet.
 

510586

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Actually I think if we put the electrons on O, then there would no longer be a carbonyl which is required?
 

plusalpha

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I had the same question as the OP... After the O attacks the carbonyl carbon, why don't the pi electrons in the carbonyl group get kicked up to the carbonyl oxygen instead? Why do the pi electrons delocalize to the nitrogen?

This is OC question #173 in the 2015 Destroyer if anyone is interested in helping out...
 
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Okay, so here's my understanding of it, and this is drawing on experience working for a silicon polymer chemist, so hopefully I don't lead you astray.

The oxygen could for a moment in time obtain the electrons, and it's quite possible it does, but it will not as readily grab the proton as nitrogen will. Often it will just quickly kick the alcohol back out and return to it's original state. Now, that being said, when the nitrogen eventually does hold that negative charge, it will be much more likely to make a nucleophilic attack and grab the proton as seen in the polymerization reaction you have outlined. Mechanisms are just the way organic chemists believe electrons moved based on the final product observed and what steps would result in lower energy states or move the reaction forward via Le Chataliers principle.

What I can tell you for sure is that how these two molecules approach each other (through the medium being used) and their orientation in space, as well as so many other reaction conditions (like temperature, length of reaction time, etc., which I'm not aware of for this problem), could contribute significantly to how the polymer is formed.

I really hope this helps you guys out! And please remember, the true professionals on this forum are Dr. Jim Romano and Nancy Steen. This is just the way I view the problem presented and hopefully it makes sense :)
 
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