Organic Chemistry
/ Acid and Base Conjugates

- Solutions 32

Draw the conjugate base for each of the following acids:

Hey guys, so in this problem we need to go ahead and figure out the conjugate base for our cyclohexanone, right? Our cyclohexane is this and then we have our ketone on that gives the one at the end, right? So, guys if we go ahead and we take a look we notice that we don't really have any super obvious hydrogen that we can withdraw, right? Because we don't have anything on me O, that would give us a much lower pKa then your regular carbon ring, right? But guys not all alkanes are exactly the same the pKa 50 is very useful when you're dealing with just a regular carbon chain or ring that doesn't have any withdrawing groups or anything that can resonate with but guys if you notice we have something that can resonate you, right? We've got this double bond and we know that this oxygen also has two lone pairs on it, right? So, guys, I'm going to go ahead and draw in our hydrogen, so I've eaten all that we've got how many different types of hydrogen here? we've got three, right? Because we've got this one right here in blue, and we know that we have two there, we've got this one here and then we've got our red here and the reason I'm only drawing it on one side is that we got this plane of symmetry, right? So if we go ahead and draw in our hydrogens, we know that this hydrogen is the same as the other blue hydrogen and this hydrogen is the exact same as the green hydrogen, right? So, guys what we need to worry about here is what, which one of these can resonate once we deprotonate, right? So if we come in and we have our NH2 minus and it comes in and deprotonates this carbon, removes that hydrogen, right? We know that we end up with is now our lone pair here, right? And we have a negative charge but now my question is, can that lone pair resonate to any other position? No it can't, right? Because on both sides. Alright, I'm going to go ahead and draw this in, explicitly the second hydrogen same thing goes with blue, we know that these carbons are fully, are fully bonded to, right? they got four bonds, two of them are hydrogen and two of them are carbons, so we cannot move those electrons, right? And if we were, try to do it in the green section, in the green hydrogen, the exact same thing would happened, okay? The only one that is eligible for a resonance is our blue one, okay? Because if we have our NH2 negative, right? I'm going to draw it a little bit better, if this comes in and deprotonates this carbon, guys, what can happen it's pretty cool, right? What we have is now this double bond O, we have a negative charge here, right? But that negative charge can resonate, right? Remember that this is a lone pair, so I'm going to go ahead and draw them explicitly, this incoming push electron onto here, kick electrons on to the O, right? And now what we end up with is this. Notice that we didn't move any atoms, all we did was move electrons, right? So guys, there we have it, that is our conjugate, that is our conjugate base for a cyclohexanone, either one of these is completely acceptable, there are just different forms, they're just different resonance structures, right? Alright guys, let's move on.