3. Which nitrogen atom in the given structure is the most...

3. Which nitrogen atom in the given structure is the most basic and explain why. H?N c 4. Which of the following choices lists the compounds in order of increasing acidity? Explain why to get credit. A) BrCH?OH < CH?NH? < CH?OH B) CH?NH? < CH?OH < BrCH?OH C) CH?OH < CH?NH? < BrCH?OH D) CH?OH < BrCH?OH < CH?NH? E) CH?NH? < BrCH?OH < CH?OH 5. Identify the Lewis acid and the Lewis base in each of the given reactions. Draw curved arrows to show which bonds are broken and formed in each reaction. a) Br + NO? b) + CH?O NO? CH? 0 + Br HO + H?O c) H

Transcript

00:01 Okay, this problem is asking us to analyze these compounds and order them in order of decreasing acidity.

00:05 So if i have three compounds total, that means that number one is going to be the most acidic, and number three is going to be the least acidic, because again, remember, decreasing acidity.

00:13 So looking at these molecules briefly, i recognize a trend.

00:17 I have two carbons and then my nh2, two carbons and then my oh, and then two carbons and then my ch3, otherwise just known as three carbons.

00:26 Okay, so the differences between these co -molecules are the third atom, of each of them, right? i have nitrogen compared to oxygen compared to carbon.

00:34 Okay, so what are those differences and those atoms have to do with the overall acidity of these molecules? okay, it has to do a lot with electron negativity.

00:41 So, electronactivity is a trend in the periodic table for different atoms or elements to want to hold onto electrons more so than other atoms, right? different atoms are happier having an electron, increased electron density than others.

00:56 So for example, if i have a quick sketch of a period of table.

01:00 It's going to look something like that.

01:01 We have fluorine over here, and then we have oxygen, nitrogen, carbon, boron, et cetera.

01:06 Right.

01:06 The electrode negativity trend goes in this direction.

01:10 That means that fluorine is going to be the most electronegative, and then oxygen, and then there are others, but then we have nitrogen, and then carbon, et cetera.

01:18 Right.

01:18 So between these three atoms, or among these three atoms, of these compounds, that means i'm going to have oxygen be the most electron negative atom of these molecules.

01:29 And then i have nitrogen and then i have carbon.

01:32 Okay.

01:32 So again, what does electron negativity have to do with overall acidity of molecules? it has to do a lot with it.

01:38 Because when comparing acidities of different molecules, one of the best ways is to look at the conjugate bases.

01:45 Because when looking at the conjugate bases, we can describe a lot about acidity.

01:49 Because the more stable the conjugate base, the more acidic, the conjugate acid is.

01:54 And vice versa.

01:55 The more, sorry, the least stable conjugate base contributes to the weaker the acid.

02:00 Okay, so let's go ahead and look at these conjugate bases and then talk a little bit about the acidities of those conjugate acids again.

02:06 Okay, so looking at this one, what is the conjugate base of this molecule? it's going to be the deprotonation of this nitrogen.

02:13 I'm going to have to take off a proton from that nitrogen.

02:15 So it's going to look like this.

02:16 Ch3, ch2, and h, in which i have lone pairs on the nitrogen, as well as a negative charge on that nitrogen.

02:24 Okay, so this is just going to be a quick aside.

02:27 A question that might arise is, why did that take off the proton associated with this nitrogen as opposed to a hydrogen associated with this carbon, for example? okay, so i'll just draw that quickly out.

02:37 That would look like this, in which i have a ch2, ch2, and then nh2, with a negative charge slash lone pairs on that carbon.

02:47 Okay, so why is this one the preferred conjugate base as opposed to this one? and that is because, again, electro -negativity differences.

02:54 So, no matter what, whenever we have an acid and we want to deprotonate it, we're always going to make the most stable conjugate base possible.

03:02 Okay, this is going to be the most stable conjugate base possible, and again, that has to do with electron negativity differences, because, as we can see, we have a negative charge on this nitrogen.

03:12 Okay, and then in the other hypothetical conjugate base, we have a negative charge on this carbon.

03:17 Okay, negative charges on nitrogen are much more favorable than negative charges than carbon, and that is simply because nitrogen is more electronegative than carbon.

03:25 Nitrogen wants to have electrons more so than carbon does, okay, because it's more electronegative...

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