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So technically this reaction is at equilibrium and we will cover that at the very end of the video here. So let's look at the mechanism for the acid catalyzed addition of water across a double bond. So here I have my alkene and I have water present with sulfuric acid, right? So sulfuric acid being a strong acid will do... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
So sulfuric acid being a strong acid will donate a proton in solution. And let's say the water molecule picks up that proton. So H2O would go to H3O+. So I'm just jumping ahead to the H3O plus ion called the hydronium ion, right? So here is my H3O plus ion, all right? So put my lone pair of electrons on there and it's ... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
So I'm just jumping ahead to the H3O plus ion called the hydronium ion, right? So here is my H3O plus ion, all right? So put my lone pair of electrons on there and it's positively charged. So what's gonna happen is the pi electrons, right? The electrons in this pi bond here are going to function as a base, right? They'... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
So what's gonna happen is the pi electrons, right? The electrons in this pi bond here are going to function as a base, right? They're going to abstract a proton. They're going to accept a proton. They're going to take, let's say, this proton right here, which would cause these two electrons in this bond to kick off ont... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
They're going to accept a proton. They're going to take, let's say, this proton right here, which would cause these two electrons in this bond to kick off onto your oxygen. So acid-base equilibrium. So I'll go ahead and make this an equilibrium arrow here. And what are we going to get if that happens, right? Well, we'r... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
So I'll go ahead and make this an equilibrium arrow here. And what are we going to get if that happens, right? Well, we're going to have, let's say that the proton added to the carbon on the right, OK? So the proton added to the carbon on the right here. So I'm saying that the blue electrons on the left are going to be... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
So the proton added to the carbon on the right here. So I'm saying that the blue electrons on the left are going to be these electrons right here, like that. And that would mean that I took a bond away from the carbon on the left, right? This carbon over here on the left, this carbon right here, used to have four bonds... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
This carbon over here on the left, this carbon right here, used to have four bonds to it. Now it has only three bonds to it. So it ends up with a plus 1 formal charge, right? So we have a carbocation in our mechanism. So what's left in this acid-base reaction? We took a proton away from H3O+, which leaves us H2O, right... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
So we have a carbocation in our mechanism. So what's left in this acid-base reaction? We took a proton away from H3O+, which leaves us H2O, right? So here we have H2O over here. So we'll go ahead and put lone pairs of electrons in on our water molecule. And we know that water can act as a nucleophile here, right? So th... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
So here we have H2O over here. So we'll go ahead and put lone pairs of electrons in on our water molecule. And we know that water can act as a nucleophile here, right? So this lone pair of electrons is going to be attracted to something that's positively charged, so nucleophilic attack on our carbocation. And this is t... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
So this lone pair of electrons is going to be attracted to something that's positively charged, so nucleophilic attack on our carbocation. And this is technically at equilibrium as well, depending on the concentrations of your reactants. So let's go ahead and show that water molecule adding on to the carbon on the left... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
OK, so the carbon on the right already had a hydrogen or a proton added on to it. And the carbon on the left is going to have an oxygen now bonded to that carbon. Two hydrogens bonded to that oxygen. And there was a lone pair of electrons on that oxygen that did not participate in any kind of bonding. This gives this o... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
And there was a lone pair of electrons on that oxygen that did not participate in any kind of bonding. This gives this oxygen right here a plus 1 formal charge. So our oxygen is now positively charged like that. And we're almost to our product, right? So we're almost there. We need one more acid-base reaction to get ri... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
And we're almost to our product, right? So we're almost there. We need one more acid-base reaction to get rid of that proton on our oxygen. So water can function as a base this time. So water comes along. And this time it's going to act as a Bronsted-Lowry base and accept a proton. So let's get those electrons in there... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
So water can function as a base this time. So water comes along. And this time it's going to act as a Bronsted-Lowry base and accept a proton. So let's get those electrons in there. So this lone pair of electrons is going to, let's say it takes that proton, leaving these electrons behind on my oxygen. Once again, I'll ... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
So let's get those electrons in there. So this lone pair of electrons is going to, let's say it takes that proton, leaving these electrons behind on my oxygen. Once again, I'll draw my equilibrium arrows here, acid-base reaction. And I'm going to end up with an OH on the carbon on the left. And the carbon on the right,... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
And I'm going to end up with an OH on the carbon on the left. And the carbon on the right, there is hydrogen like that. So I added water. I ended up adding water across my double bond. And to be complete, this would regenerate my hydronium ion. I'd get H2O plus H plus would give me H3O plus. So hydronium is regenerated... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
I ended up adding water across my double bond. And to be complete, this would regenerate my hydronium ion. I'd get H2O plus H plus would give me H3O plus. So hydronium is regenerated. And so there you go. So remember, a carbocation is present. So you have to think about Markovnikov addition. | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
So hydronium is regenerated. And so there you go. So remember, a carbocation is present. So you have to think about Markovnikov addition. And since a carbocation is present, you have to think about possible rearrangements. So Markovnikov and rearrangements. Let's take a look at an example where you have a rearrangement... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
So you have to think about Markovnikov addition. And since a carbocation is present, you have to think about possible rearrangements. So Markovnikov and rearrangements. Let's take a look at an example where you have a rearrangement here. So let's look at a reaction. So let's start off with, let's look at this as our st... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
Let's take a look at an example where you have a rearrangement here. So let's look at a reaction. So let's start off with, let's look at this as our starting alkene. And let's go ahead and think about the mechanism. So we know H3O plus is going to be present. So H3O plus right here. So we're adding our alkene to a solu... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
And let's go ahead and think about the mechanism. So we know H3O plus is going to be present. So H3O plus right here. So we're adding our alkene to a solution of water and sulfuric acid. And our first step in the mechanism, the pi electrons are going to function as a base and take a proton from our hydronium ion, leavi... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
So we're adding our alkene to a solution of water and sulfuric acid. And our first step in the mechanism, the pi electrons are going to function as a base and take a proton from our hydronium ion, leaving these electrons in here, letting them kick back off onto the oxygen. So let's see what we would have from that acid... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
And I realize I didn't draw an equilibrium arrow here. I'm more concerned with getting the right product. So this is our carbon skeleton. And which side do we add the hydrogen? Which side of the double bond? Do we add the proton to the left side, or do we add the proton to the right side? Well, we want to form the most... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
And which side do we add the hydrogen? Which side of the double bond? Do we add the proton to the left side, or do we add the proton to the right side? Well, we want to form the most stable carbocation we possibly can. And if we add the proton to the left side of our double bond, we end up with a secondary carbocation.... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
Well, we want to form the most stable carbocation we possibly can. And if we add the proton to the left side of our double bond, we end up with a secondary carbocation. This carbocation right here is secondary, because this carbon that has the positive charge is bonded to two other carbons. So this is a secondary carbo... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
So this is a secondary carbocation. If we had added the proton on to the other side of the double bond, we would have a primary carbocation. So secondary carbocation is more stable. But can we form something that's even more stable than a secondary carbocation? And of course we can. We can form a tertiary carbocation i... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
But can we form something that's even more stable than a secondary carbocation? And of course we can. We can form a tertiary carbocation if we think about the possibility of a hydride shift. So right here, there is a hydrogen attached to that carbon. And if the proton and these two electrons are going to move over here... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
So right here, there is a hydrogen attached to that carbon. And if the proton and these two electrons are going to move over here and form a new bond with our positively charged carbon, so we get a hydride shift at this point. So let's draw what would result from that hydride shift. We move to hydrogen over here. That ... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
We move to hydrogen over here. That took a bond away from this carbon. So that is the carbon that's going to end up with the positive charge now. So we added a bond to what used to be our secondary carbocation carbon. And so that formal charge goes away. The formal charge moves to this carbon right here, which is now a... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
So we added a bond to what used to be our secondary carbocation carbon. And so that formal charge goes away. The formal charge moves to this carbon right here, which is now a tertiary carbocation. If you look at the carbons connected to that carbon, this is a tertiary carbocation. So we know tertiary carbocations are m... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
If you look at the carbons connected to that carbon, this is a tertiary carbocation. So we know tertiary carbocations are more stable than secondary. So now we're at the step of the mechanism where a water molecule is going to come along. So we have a water molecule, which is going to function as a nucleophile and atta... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
So we have a water molecule, which is going to function as a nucleophile and attack our positively charged carbon like that. So let's go ahead and draw what the result of that nucleophilic attack would look like. So we have our carbon skeleton. And we have an oxygen atom now bonded to that carbon. So two hydrogens here... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
And we have an oxygen atom now bonded to that carbon. So two hydrogens here. And once again, one lone pair of electrons did not participate in that reaction, giving this oxygen a plus 1 formal charge. And then finally, instead of showing the last step, a water molecule comes along, takes one of the protons, off of our ... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
And then finally, instead of showing the last step, a water molecule comes along, takes one of the protons, off of our positively charged oxygen, and gives us our major product, with the OH adding on to this carbon right here. So this is a major product. This is our major product. And we would get some of the alcohol t... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
And we would get some of the alcohol that forms from the secondary carbocation. So a minor product, that's what we would get if this oxygen had attacked our secondary carbocation. And you will get some of that. But if your test asks for the major product, you should show the product of this rearrangement. Now, we're lu... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
But if your test asks for the major product, you should show the product of this rearrangement. Now, we're lucky in this instance because our product here, this carbon right here, ends up not being a chirality center. Because I have two methyl groups attached to that carbon. So I don't have to worry about my stereochem... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
So I don't have to worry about my stereochemistry here. Let's do a reaction where we do have to worry about stereochemistry. So let's look at this reaction right here. So we take this as our starting alkene. So I'll put the double bond right there. And let's make that a little bit more clear here. So the double bond is... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
So we take this as our starting alkene. So I'll put the double bond right there. And let's make that a little bit more clear here. So the double bond is between these two carbons right here. And once again, we're going to add water and sulfuric acid, so H2SO4. And when we think about the mechanism, we know that we're g... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
So the double bond is between these two carbons right here. And once again, we're going to add water and sulfuric acid, so H2SO4. And when we think about the mechanism, we know that we're going to add a proton to one side of the double bond. And the other side of the double bond is going to end up being our carbocation... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
And the other side of the double bond is going to end up being our carbocation. So the first thing to think about is, OK, which one of these two sides is going to get the proton? We want to form the most stable carbocation we can. So the proton's going to add on to the carbon on the left. So if I can go ahead and show ... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
So the proton's going to add on to the carbon on the left. So if I can go ahead and show the intermediate here. So for an intermediate, we don't need that arrow. We'll just go ahead and show the proton adding on to the carbon on the left. So we get an H here. And then the carbon on the right of the double bond now ends... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
We'll just go ahead and show the proton adding on to the carbon on the left. So we get an H here. And then the carbon on the right of the double bond now ends up being our carbocation. So this is now positively charged like that. And remember, when we have a carbocation, this carbon is bonded to three other atoms. You ... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
So this is now positively charged like that. And remember, when we have a carbocation, this carbon is bonded to three other atoms. You have to think about what that looks like. So remember, carbocations, when something's bonded to three other carbons, you get this situation, where everything is in the same plane. sp2 h... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
So remember, carbocations, when something's bonded to three other carbons, you get this situation, where everything is in the same plane. sp2 hybridized carbon exhibits trigonal planar geometry, also with your unhybridized p orbital like that. So this is your sp2 hybridized carbocation situation here. So when your wate... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
So when your water molecule comes along and acts as a nucleophile, your water molecule could end up attacking from the top here, or it could end up attacking from below here. So that's where the stereochemistry comes in. So let's go ahead and take our carbocation, and let's see if we can draw the products that would re... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
And then we'll just go ahead and think about the proton going away in our heads for the mechanism. So when you have enough practice, you can do steps in the mechanism in your head. So let's see, what would we get for our two possible products? Well, the OH could have added this way, which would push that methyl group t... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
Well, the OH could have added this way, which would push that methyl group there away from us. So the methyl group would be going away from us. Or the OH could have added from the opposite side. The OH could have been the one back here, and that would have pushed the methyl group out like this. And we know that these a... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
The OH could have been the one back here, and that would have pushed the methyl group out like this. And we know that these are chirality centers. We know that this is our chirality center on these guys. So we get enantiomers here. 50-50% racemic mixture for our products. And we see that the OH adds on in a Markovnikov... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
So we get enantiomers here. 50-50% racemic mixture for our products. And we see that the OH adds on in a Markovnikov fashion. It adds on to the side that's the most stable carbocation here. So one more thing about this reaction. So let's do one that doesn't have any stereochemistry to worry about, and we'll try to make... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
It adds on to the side that's the most stable carbocation here. So one more thing about this reaction. So let's do one that doesn't have any stereochemistry to worry about, and we'll try to make a different point about this reaction here. So this is our reaction. So we're going to add water to this. And we'll put sulfu... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
So this is our reaction. So we're going to add water to this. And we'll put sulfuric acid up here. And we'll make our arrow a little bit different to illustrate the point here. So we could go, let's go ahead and draw an equilibrium arrow here. So let's say this whole reaction is at equilibrium. So let me get this equil... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
And we'll make our arrow a little bit different to illustrate the point here. So we could go, let's go ahead and draw an equilibrium arrow here. So let's say this whole reaction is at equilibrium. So let me get this equilibrium arrow in here. And our product. So if we don't have to worry about stereochemistry, we think... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
So let me get this equilibrium arrow in here. And our product. So if we don't have to worry about stereochemistry, we think, OK, really all I have to do is think about which side of the double bond do I put my OH. And again, in Markovnikov addition, the more substituted carbon is the one that's going to get your OH. So... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
And again, in Markovnikov addition, the more substituted carbon is the one that's going to get your OH. So the more substituted carbon would be the one on the left here. So for your product, you would say, OK, I know all I have to do is really just go and put my OH in there on the more substituted carbon, and I'm done.... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
I don't have to worry about stereochemistry for this reaction. I don't have to worry about rearrangements. It's the tertiary carbocation, so that takes care of it. Now, this reaction is technically at equilibrium. And you could think about water as being one of your reactants. So if water is one of your reactants, and ... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
Now, this reaction is technically at equilibrium. And you could think about water as being one of your reactants. So if water is one of your reactants, and you think about general chemistry, Le Chatelier's principle, how do you shift in equilibrium? If you want to make more of your product, if you want to make more of ... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
If you want to make more of your product, if you want to make more of this, your product, your alcohol, one way to do it would be to increase the concentration of water. So if you increase the concentration of water, the equilibrium will shift to decrease the stress that was put on the system. So you're going to get a ... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
But remember, if you have an alcohol for a product, if you react this alcohol with sulfuric acid, that's an E1 elimination reaction that we saw in earlier videos. So acid catalyzed dehydration, the addition of concentrated sulfuric acid to your alcohol can actually form your alkene. So that's a reaction that we saw ear... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
So you could go back the other way. You could go back to the left. Let's say you decreased the concentration of water. You could shift the equilibrium to the left, and you would actually form your alkene here. So the way to control your equilibrium is if you want to go to the right, you just dilute your sulfuric acid. ... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
You could shift the equilibrium to the left, and you would actually form your alkene here. So the way to control your equilibrium is if you want to go to the right, you just dilute your sulfuric acid. You add more water to it, which would increase this concentration. If you want to shift the equilibrium to the left, yo... | Hydration Alkenes and Alkynes Organic chemistry Khan Academy.mp3 |
Hades is also the name of the god that ran the Greek underworld, Zeus's oldest brother. And it was an appropriate name, although the idea of the ancient Greek notion of the underworld isn't exactly the more modern notion of hell. But it was a hellish environment. You had all this lava flowing around. You had things imp... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
You had all this lava flowing around. You had things impacting the Earth from space. And as far as we can tell right now, it was completely inhospitable to life. And to make matters worse, even though the Earth started to cool down a little bit, maybe the crust became a little bit more solid. Maybe the collisions start... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
And to make matters worse, even though the Earth started to cool down a little bit, maybe the crust became a little bit more solid. Maybe the collisions started to happen less and less as we started to go a few hundred million years fast forward after Thea rammed into the early Earth and formed the moon. There was some... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
And right now the consensus is that whatever we are descended from would have had to come about after the late heavy bombardment. Because this was a time where so many things from outer space were hitting Earth that it was so violent that it might have killed off any kind of primitive, self-replicating organisms or mol... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
That is the sun. This is the asteroid belt that's outside the orbits of the inner rocky planets. That Uranus and Neptune, their orbits moved outward. And I'm not going to go into the physics, but what that caused is gravitationally it caused a lot of the asteroids in the asteroid belt to move inward and start impacting... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
And I'm not going to go into the physics, but what that caused is gravitationally it caused a lot of the asteroids in the asteroid belt to move inward and start impacting the inner planets. And of course, Earth was one of the inner planets. And I should make the sun like orange or something, not blue. I don't want you ... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
I don't want you to think that's Earth. And it also impacted the moon. And it's more obvious on the moon because the moon does not have an atmosphere to kind of smooth over the impact. So the consensus is that only after the late heavy bombardment was Earth kind of ready for life. And we believe that the first life for... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
So the consensus is that only after the late heavy bombardment was Earth kind of ready for life. And we believe that the first life formed 3.8 to 4 billion years ago. Remember, G for giga, 4 billion years ago. And when we talk about life at this period, we're not talking about squirrels or panda bears. We're talking ab... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
And when we talk about life at this period, we're not talking about squirrels or panda bears. We're talking about extremely simple life forms. We're talking about prokaryotes. And let me give you a little primer on that right now, although we go into much more detail in the biology playlist, we're talking about prokary... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
And let me give you a little primer on that right now, although we go into much more detail in the biology playlist, we're talking about prokaryotes. And I'll compare them to eukaryotes. Prokaryotes are, for the most part, unicellular organisms that have no nucleuses. They also don't have any other membrane-bound, what... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
They also don't have any other membrane-bound, what we'd call organelles, or these little parts of the cells that perform specific functions like mitochondria. So their DNA is just kind of floating around. So let me draw this character's DNA. So it's just floating around, just like that. And prokaryote literally means ... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
So it's just floating around, just like that. And prokaryote literally means before kernel or before a nucleus. Eukaryotes do have a nucleus where all of their DNA is. So this is the nuclear membrane, and then all of its DNA is floating inside of the nucleus. And then it also has other membrane-bound organelles. Mitoch... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
So this is the nuclear membrane, and then all of its DNA is floating inside of the nucleus. And then it also has other membrane-bound organelles. Mitochondria is kind of the most famous of them. So it also has things like mitochondria. We'll learn more about that in future videos. Mitochondria, we believe, is essential... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
So it also has things like mitochondria. We'll learn more about that in future videos. Mitochondria, we believe, is essentially one prokaryote crawling inside of another prokaryote and kind of starting to become a symbiotic organism with each other. But I won't go into that right now. But when we talk about life at thi... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
But I won't go into that right now. But when we talk about life at this period, we're talking about prokaryotes. And we still have prokaryotes on the planet. Bacteria and archaea are examples of prokaryotes. And just to give you a little bit of a tidbit right here, this kind of shows our current understanding of where ... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
Bacteria and archaea are examples of prokaryotes. And just to give you a little bit of a tidbit right here, this kind of shows our current understanding of where we think things branched off from. So at this point of the tree is some common ancestor to prokaryotes and eukaryotes. So these are the prokaryotes right over... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
So these are the prokaryotes right over here, the bacteria and the archaea. And here is the eukaryotes. And this first living thing, or this first set of living things, we think might have just been some type of self-replicating molecules. And slowly some membrane might have come around and became a little bit more org... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
And slowly some membrane might have come around and became a little bit more organized. DNA, RNA, maybe RNA was that original self-replicating molecule, became the method of kind of transmitting information from one generation to the next. So it's really still an open question of exactly what that first life is, or eve... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
But based on studying the genetic makeup of current organisms, this is how we think the tree of life came about. So we have one common ancestor, then they broke apart, and then the archaea and eukaryotes have a common ancestor that's different from the bacteria. And we'll talk more about that in the future. And this ri... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
And this right here, just so you can visualize it, this is an example of bacteria. This is E. coli or Escherichia coli. It's just an example of bacteria. It comes in a bunch of shapes and forms. But it's a prokaryotic life form. And the earliest life forms we also think were anaerobes. These are things that did not nee... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
It comes in a bunch of shapes and forms. But it's a prokaryotic life form. And the earliest life forms we also think were anaerobes. These are things that did not need, one, that they did not need oxygen, and they, for the most part, found oxygen poisonous. And the earliest life forms also probably did not perform phot... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
These are things that did not need, one, that they did not need oxygen, and they, for the most part, found oxygen poisonous. And the earliest life forms also probably did not perform photosynthesis. They might have gotten their energy from other sources, chemically, from this kind of extremely volatile environment that... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
So if we fast forward a little bit, and this is actually a major event in the history of Earth. And these are huge timescales we're talking about. I mean, remember, I'm kind of just nonchalantly saying, oh, 4.6 billion years ago to 3.8 billion years ago, that's just 800 million years. Remember, and I'll talk about this... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
Remember, and I'll talk about this, grass has only existed for 50 million years. This is 800 million years. Humans and chimpanzees only diverged 5 million years ago. This is 800 million years we're talking about. From ancient Greece to now, we're only talking about 2,500 years. You multiply that times 1,000. You multip... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
This is 800 million years we're talking about. From ancient Greece to now, we're only talking about 2,500 years. You multiply that times 1,000. You multiply that times 1,000, you get 2.5 million years. And this is 800 million years we're talking about. So these are extremely huge periods of time. And that's why we call... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
You multiply that times 1,000, you get 2.5 million years. And this is 800 million years we're talking about. So these are extremely huge periods of time. And that's why we call them eons. Eons are 500 million to a billion years. Now, the dividing line between the Hadean Eon and the Archean Eon, and it's kind of a fuzzy... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
And that's why we call them eons. Eons are 500 million to a billion years. Now, the dividing line between the Hadean Eon and the Archean Eon, and it's kind of a fuzzy dividing line, but most people place it about 3.8 billion years ago, is kind of the earliest rocks that we can observe. And so we have rocks that are rou... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
And so we have rocks that are roughly 3.8 billion years ago, so we kind of put that as the beginning of the Archean Eon. And so there's two things there. One, rocks have survived from the beginning of the Archean Eon, and also that's roughly when we think that the first life existed. And so we're now in the Archean Eon... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
And so we're now in the Archean Eon. And you might say, oh, maybe Earth is a more pleasant place now. But it would not be. It still has no to little oxygen in the environment. If you were to go to Earth at that time, it might have looked something like this. It would have been a reddish sky. You would have had nitrogen... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
It still has no to little oxygen in the environment. If you were to go to Earth at that time, it might have looked something like this. It would have been a reddish sky. You would have had nitrogen and methane and carbon dioxide in the atmosphere. There would have been nothing for you to breathe. There still would have... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
You would have had nitrogen and methane and carbon dioxide in the atmosphere. There would have been nothing for you to breathe. There still would have been a lot of volcanic activity. This right here, these are pictures of stromatolites. And these are formed from bacteria that are bringing in sediment particles, and ov... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
This right here, these are pictures of stromatolites. And these are formed from bacteria that are bringing in sediment particles, and over time, these things get built up. But the most significant event in the Archean period, at least in my humble opinion, was what we believe started to happen about 3.5 billion years a... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
And this is prokaryotes, or especially bacteria, evolving to actually utilize energy from the sun to actually do photosynthesis. And the real fascinating byproduct of that, other than the fact that they can now use energy directly from the sun, is that it started to produce oxygen. So it starts to produce oxygen. And a... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
And at first, this oxygen, even though it was being produced by the cyanobacteria, by this blue-green bacteria, it really didn't accumulate in the atmosphere, because you had all of this iron that was dissolved in the oceans. And let me be clear, all of the life that we're going to be talking about for really the next ... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
The land was being irradiated. The land was just a completely inhospitable environment for life. So all of this was occurring in the ocean. And so the first oxygen that actually got produced, it actually, instead of just being released into the atmosphere, it ended up bonding with the iron that was dissolved in the oce... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
And so the first oxygen that actually got produced, it actually, instead of just being released into the atmosphere, it ended up bonding with the iron that was dissolved in the ocean at that time. So it actually didn't have a chance to accumulate in the atmosphere. And when we fast forward past the Archean period, we'r... | Beginnings of life Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
Let's start with an aldehyde. Just to refresh your memory about how to recognize an aldehyde, there's a carbonyl present, a carbon double bonded to an oxygen, and there's an alkyl group on one side and a hydrogen on the other side. If we wanted to name this extremely simple molecule over here on the left, we know there... | Nomenclature of aldehydes and ketones Aldehydes and ketones Organic chemistry Khan Academy.mp3 |
If we look at a four-carbon aldehyde right over here on the right, when you number an aldehyde, you want to make your carbonyl carbon number one, so one, two, three, and four. We have a four-carbon aldehyde. What we're going to do is drop the E and add AL for aldehyde. This would be butanal. A four-carbon aldehyde is b... | Nomenclature of aldehydes and ketones Aldehydes and ketones Organic chemistry Khan Academy.mp3 |
This would be butanal. A four-carbon aldehyde is butanal with an AL ending like that. Let's go ahead and look at some more examples. Once again, we're going to number to give our carbonyl carbon the lowest number possible. The aldehyde is going to take priority over things like double bonds and alkyl groups and halogen... | Nomenclature of aldehydes and ketones Aldehydes and ketones Organic chemistry Khan Academy.mp3 |
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