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Video Solution: The structure of montelukast, an antiasthma drug, is shown h...

Problem

The structure of montelukast, an antiasthma drug, is shown here. 

(b) Use Table 1.8 to identify the most acidic and most basic sites in the molecule. (Although you won't find an exact matchin structure, make a prediction based on analogy with similar groups in simpler molecules.)

Video Transcript

So guys, looking at this molecule I can find the most acidic portion and the most basic, okay? this is the most acidic portion because it's got a pKa of about 5, okay? The most basic portion here is this nitrogen that can make more than three bonds, right? And we know that it's got this lone pair here, okay? So, actually what happens in equilibrium is that we get this, we get a carboxylate over here and we get our protonated nitrogen here, okay? With a positive charge and guys, what happens now is that if we treat this with sodium hydroxide? Well, what we get is our neutral nitrogen there, right? We get it back with its negative charge, right? And the reason for the, I'm sorry, isn't neutral charge, it's lone pair, right? And the reason for that is that what has this hydrogen is pKa is about 10, okay? Probably a little bit lower because of all those resonance that I can do, right? But our pKa for our alcohol over here is 16, again probably a little bit lower because it would be able to resonate, but let's just hold them as 10 and 16, okay? Closest to what Johnny has taught us using the pKa chart, so if we treated it with just one equivalent of sodium hydroxide it would go for the most acidic thing, right? And in fact our nitrogen here is about a million times more acidic than this over here, because 16 minus 10 is 6 and 10 to the 6, right? So we end up with is this just our lone pair on it again, and if we were to go ahead and treat it with hydrochloric acid what we end up with, right? It's just one equivalent hydrochloric acid is we'd end up reprotonating this guy over here, after we treated with sodium hydroxide, if we hadn't treated it with sodium hydroxide to begin with we would end up with both of these being protonated. Alright I hope that makes sense, let me know if you guys have any questions, let's move on.

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