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Current time:0:00Total duration:11:18

Video transcript

we now know how to name aldehydes and ketones and what I want to do in this video is show a mechanism for actually creating one and in particular we're going to create a ketone so let's say we've got ourselves some benzene and the first step of this reaction the benzene is just going to sit and watch we've got some benzene and we've got some acetyl chloride acetyl chloride so it looks almost like an aldehyde or ketone but instead of having a carbon chain here or hydrogen we're going to have a clora a chlorine atom right over there so this is acetyl chloride acetyl chloride sometimes called acyl chloride this is acetyl chloride and we're going to have an aluminum chloride catalyst and a catalyst means that it participates in the reaction but it enters the reaction and it exits the reaction is the same molecule so it just catalyzes it but it doesn't disappear it just changes halfway but then goes back to what it was before so we have some aluminum chloride and it's bonded to one two three one two three chlorines now the first step of this reaction is to turn this acetyl chloride into a good electrophile turn it into something that's really good at nabbing electrons so good that it can break the aromatisse 'ti of the benzene ring and essentially add itself to the benzene ring this is actually the same mechanism we saw with I think electrophilic aromatic substitution I always have trouble remembering the names what I was imagining it's electrophilic substitution either way it's this very similar mechanism and actually that what we're going to show in this video is called friedel-crafts a salacious because this right here this right here is called an acyl group this right here is called an acyl group and we're essentially going to acyl eight the benzene ring we're going to add this group right here to the benzene ring so enough of what's going to happen let's actually see it happen so the first thing to realize this aluminum chloride the aluminum in it is electron deficient at a first cut if you just look at the periodic table if you look at the periodic table you have these chlorines over here pretty electronegative aluminum is in the same row but chlorines way more to the right so it's more electronegative so the chlorines are going to hog the electrons in this molecule the chlorines are going to hog so the aluminum is going to have a partial positive charge chlorines will have slightly partial negative charge on top of that you see aluminum is a group 3 is a group 3 element 1 2 3 so it has 3 valence electrons you see that right here 1 2 3 nowhere close to the magic number of 8 even when it covalently bonds with these chlorines it can only pretend like it has 6 electrons it can kind of pretend like it has these chlorines electrons over here but that only gets it to 6 so it would really like to have more electrons to get closer to that to get closer to that magic 8 number so what you can imagine is is a situation where this chlorine this chlorine on the acetyl chloride this chlorine it's already hogging this green electron from this carbon it was already doing that it's more electronegative so this thing over here will actually be given to the aluminum and so it will then have a bond with the chloride so if that happened what is our reaction look like so if that happened what does everything look like our aluminum our aluminum our aluminum chloride or what was formerly aluminum chloride now just gained an electron and with it and with it it is now bonded to another chlorine so it is now bonded to a another chlorine and since it gained an electron let me make it very clear this is an L my penmanship is deteriorating that's an L and since this aluminum gained an electron it now has a negative charge and normally a negatively charged thing isn't that stable but these guys are electronegative so they might hog a lot of that Elect of that negative charge and on top of it aluminum can now pretend like it has eight electrons it has one two three four five six seven eight when you Kaval covalently bond to someone you can kind of pretend like you have their electrons as well so now you have this anion that was formed from the aluminum chloride and now the acetyl chloride the acetyl chloride will look like this the acetyl chloride let's scroll down a little bit let me make it clear we're in the next step of the reaction we are in the next step of the reaction what was formerly the acetyl chloride has now lost the chloride so it's now really just a acyl group so you have the carbonyl bonded to a ch3 a methyl just like that this guy lost his electron so now he has a positive he has a positive charge and this is actually it's not that stable and you're going to see it's actually highly reactive it's a very good electrophile it wants to steal other people's electrons but it is it will it can exist for a short amount of time especially because it is resonant stabilizing so how is it resonance stabilized well this oxygen over here has two electron pairs that I didn't draw before and let me draw the second one in a different color it has two electron pairs like that so you could imagine a situation the electron this guy this carbon is already he has a positive charge and this oxygen is more electronegative is already hogging his electrons maybe wants to give back a little bit say hey this is positive these electrons all the electrons are hanging out here they'd be attracted to the positive and you could imagine one of these electrons being given back to the carbon and if that happened if that happened then we have another resonance form we have another resonance form that looks like this so this was our original molecule or that's our original or what it looked like we still have this double bond right over there but now this or that pair of electrons now this pair of electrons now forms another bond this electron over here is now on the oxygen end this electron over here is now on the carbon end and now they have a now they have a triple bond and what happened this positive carbon gained an electron so it's now neutral and the neutral oxygen lost an electron so it is now positive and you can imagine this is not a very stable that you wouldn't see this just floating around by itself but it does stabilize this entire configuration it stabilizes this molecule so you can show that these are alternates resonance resonantly stabilized structures right there but as I said these aren't super stable this guy really really really wants to react and now this is where benzene comes into the mix and actually let me draw a little dividing line here just so we know that this was a separate stage of our reaction so that was the first stage then we go over here and now benzene comes into the mix the benzene is floating around so we have our benzene benzene floating around just like that and then I'm going to draw one of the hydrogen's on one of the benzene's all of these car on one of the carbons all of these carbons have hydrogen's on them I just won't draw them all it just makes things complicated but this guy we said is a really good electrophile and it's you have to be a really good electrophile to attract electrons from a benzene ring to break its aromatisse ax t but if it bumps or into this guy in just the right way just the right angle you could imagine that this electron on this carbon right here gets swiped by the acyl group gets swiped by the acyl group so then what do we have so now I will go I will go back in this direction so you have what was a benzene ring so what was a benzene ring it still has we could draw the double bonds here and here here and here and we of course have this hydrogen we have this hydrogen but now this bond which was the double bond there is now bonded to the acyl group so it has that blue electron that the acyl group nabbed and let me draw the acyl group and I'll flip it over I'll flip it over so that we have the methyl on the right-hand side so it's a carbonyl bonded to a ch3 it was positive it now gained an electron it is now neutral it is now neutral this carbon over here lost an electron so it is now positive so it is now it is now positively charged now we mentioned the aluminum chloride is a catalyst so it won't just sit around there as the anion it has to go back to being aluminum chloride so let's bring the aluminum chloride back into the scene so we have our aluminum chloride let me copy and paste it copy and paste so we have our aluminum chloride here and so you can imagine that the benzene ring wants to go back to being aromatic so this this electron right here this electron right here on the hydrogen this electron right here on the hydrogen might really want to go back to this carbon right over here this carbo cation and at the same time if the aluminum if this anion now passes the hydrogen in just the right at just the right angle at the right time while this guy is attracted to this carbon this chlorine can give this green electron to the hydrogen to the hydrogen nucleus which is really just a proton and then the hydrogen's electron can be taken up by what was this carbo cation and then what did we have then we have a situation where our benzene ring is reformed we have the aromaticity again we have that double bond that double bond and now we have this double bond again although now it's using the electron from the hydrogen and we still and now we've substituted this hydrogen which is essentially this acyl group this acyl group right over here so we have a carbon double bonded to an oxygen bonded to a methyl group and now the aluminum or this-this-this anion lost it's an electron so it goes back to just being straight-up aluminum chloride aluminum it goes back to just being straight-up neutral electron deficient aluminum chloride and we've done we're done we've just ASA lized this benzene ring and that's why this is called this mechanism is called friedel-crafts Friedel riedle friedel-crafts crafts isolation isolation and Friedel is actually a former former president of MIT and i did some reading on this and he apparently he did not have a ph.d but because he discovered friedel-crafts isolation and this friedel-crafts actually alkylation as well they said hey you know this guy's a smart dude let's make him the president of MIT but I just wanted to show you that this is a reaction for creating a ketone so this create this this ketone that we've created is a seed of fien own which we've seen before which we learned in is a common name this molecule that we learned in the first ketone video and I'll write it in purple Osito Osito be known and we're done