how to find the most acidic hydrogen This is a topic that many people are looking for. cfiva.org is a channel providing useful information about learning, life, digital marketing and online courses …. it will help you have an overview and solid multi-faceted knowledge . Today, cfiva.org would like to introduce to you Ch 2 OHV “Identifying the most acidic proton in a molecule”. Following along are instructions in the video below:
This tutorial. Were going to learn how to compare the various protons in a a compound and determine. Which proton is the most acidic proton.
Lets take this as an example lets go ahead and draw all of the protons that are in this compound. And we essentially have four different kinds of protons. Theres a these protons here this one these two and these and we need to decide.
Which proton is the most acidic is one of these protons. The most acidic or this one or one of these or one of these now weve already seen a tutorial for how to compare the acidity of two different compounds and in that tutorial. We saw that there are four factors that we use for comparing stability of conjugate bases.
What atom is the charge on resonance induction. And what orbital is the lone parent. Now might be a good time to go and review that tutorial and go over the rules for comparing acidity of protons.
Were going to use that here to do the exact same thing as we did over there. But now instead of comparing two different compounds for example instead of comparing one compound with another compound. And saying is this proton more acidic or is this proton more acidic now.
Were looking in one molecule and saying. Which proton in the molecule is the most acidic proton and in order to do that were going to need to draw the conjugate base of each one this would be the conjugate base. If we pulled off one of these protons this would be the conjugate base.
If we pulled off this proton. This would be the conjugate base. If we pulled off one of these protons and finally this would be the conjugate base.
If we pulled off one of these protons and what we need to do now is compare all four of these possible conjugate bases using our four factors and determining which of these conjugate bases is the most stable whichever one is the most stable that will tell us. Which proton was the most acidic proton. Lets see how this works lets start with what atom is the charge on here are the charges on a carbon atom here.
Its on a nitrogen here. Its on a carbon and here its on a nitrogen. So we immediately gravitate towards negative charge being on nitrogen negative charge being on nitrogen is better the negative charge being on carbon or here again on carbon.
Why because nitrogen is more electronegative and can better handle the negative charge than carbon can so immediately gravitate towards this one. And this one both of which have n minus. Then we move to our second factor resonance and we look for where we have resonance.
This one doesnt have any resonance. Its c minus with no resonance. We can pretty much cross that one off here we have c minus.
But it does have resonance. Theres a resonance structure kicking up the negative charge up onto the oxygen. Here.
There is no resonance. And here. There is resonance.
Kicking up onto the oxygen. So although. This is n minus.
But we have an n minus. Here with resonance. So we can cross this one off.
Were left between these two. We just have to decide is it better to have the negative charge spread out between carbon and an oxygen atom or is it better to have the negative charge spread out between a nitrogen and an oxygen and the answer is when we compare nitrogen oxygen is better than carbon and oxygen so in fact lets go ahead and draw out that resonance structure. Oh ran out of room.
Here on the side of the screen. So instead of writing. It as nh.
I put one h up here and one h down. Here. But here are our resonance structures.
And we see that we have the negative charge spread out between nitrogen and oxygen and thats going to be better. We dont have any inductive effects or orbital effects. Here.
So. This is going to be the more stable conjugate base. The most stable conjugate base of all the possibilities.
And the most stable conjugate base comes. When we have a negative charge right here on this nitrogen. So.
Which proton is the most acidic. The most acidic proton is the one that gives us the most stable negative charge. The most stable conjugate base.
And thats this one right here. If we pull off this proton. We get a negative charge on the nitrogen atom right here.
And that negative charge is resonance. Stabilized up onto the oxygen. So we see that when were comparing the protons in one molecule.
We use the exact same procedure that we use when we were comparing protons and different molecules. That is we for each proton. We imagine the conjugate base and then we compare those conjugate bases.
Using our four factors. What atom is the charge on resonance induction and orbitals. And after using those four factors.
We can determine. Which conjugate base is the most stable conjugate base. And that in turn tells us.
Which proton is the most acidic proton. .
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