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Current time:0:00Total duration:8:03

Video transcript

let's explore another mechanism that we can have with the key to and actually it an aldehyde could undergo a very similar actually the same type of reaction so let's say that I had a ketone that looked like this that's my draw my carbonyl group just like that and then it is bonded to a carbon that is bonded to two other ch3 groups and just to make it clear I mean there's three hydrogen's off of this carbon they're implicitly but I'm going to draw the fourth bond here which is to a hydrogen because this hydrogen is going to be important for this reaction now we know that the oxygen has two lone pairs of electrons let me draw it up here and let's just imagine it's floating around in some water and we know that in water there is some concentration of hydronium and let's say that one of the hydronium is right over here so let's see hydronium is just a positively charged so this right here let make it clear this in a different color this is what water looks like this is what water looks like and if water gives away an electron to a proton it looks it looks like this it is hydronium and then it only has one lone pair of electrons it gave away one of the other one of the other electrons and it's other lone pair to a proton so you could imagine a reality well it's like hey I could grab that proton from this hydronium and then this will turn back into water and in that situation the mechanism would look like this this electron let me do it in a different color this blue electron gets given to this this proton if they just bump into each other just right and then the hydrogen's electron gets taken back by what will become a water molecule so if that happens what do our molecules now look like so now our what was a ketone looks a little bit different than a ketone so it looks like this I change it to a slightly lighter color of green so it looks like that we have our lone pair over here but we no longer have this lone pair at this end we still have this magenta electron but now it is in a covalent bond with the blue electron which was now given to the hydrogen proton go up a little bit it was given to this hydrogen proton up here it was given to that hydrogen proton up here and then this hydronium molecule it took back an electron and now it is just neutral water it is just it is now just neutral water took back that magenta electron so now it has two lone pairs again so it is just neutral water now this since this oxygen up here in the carbonyl group gave away an electron it now has a positive charge it now has a positive charge but this is actually resonance stabilized you could see that this is or you could maybe see that this would be in resonance or another resonance form of this would be would be if this guy is positive so he wants to gain an electron so maybe he takes an electron from this carbon the carbon in the carbonyl group right over there so if he takes that electron so then the other resonance form would look like this you would have and we do it in the same colors you have now only a single bond with this oxygen up here this carbon down here is still bonded to the same carbon and then this carbon over here we could call this an alpha carbon this is an alpha carbon to the carbonyl group it still has a hydrogen on it right over there and this oxygen since it gained this magenta electron so now it has two lone pairs again it has this pair over there and then it gained it has this electron and this electron so it has another lone pair and of course it has the bond to the hydrogen it has the bond to the hydrogen since it gained an electron it is now neutral this carbon lost an electron so now it is positive so now this carbon this carbon right over here is positive and these two are two different resonance forms so they help stabilize each other and the reality is actually someplace in between and I could actually draw it in brackets to show that these are two resonance structures now you can imagine just as likely and actually I shouldn't just draw this as a one-way arrow because this guy could take a hydrogen from this hydronium or the hot or a water could take a hydrogen from this guy so this actually could go into in both directions let me make that clear this could go in both directions you can say that they're in equilibrium with each other that you're just as likely to go in that direction is you really for the most part are to go in the other direction but you can now imagine okay this is now turned in from a carbonyl group this is now a hide this is now an OHA piss is now turned into an alcohol though we have this carbo cation here that this does not like being positive and so you can you can imagine where this electron right here being a track on this hydrogen nucleus might want to go really bad to this carbo cation and it just needs something to nab the proton off for it to go there and the perfect candidate for that would just be a water molecule we have this water floating around so let me draw another water molecule just like this it has two lone pairs it can act as a weak base it can give one of its electrons to this hydrogen proton if it does that at the exact same time bumps into it in the exact same way this electron can then go to the carbo cation and if that happened if that happened and you can go in either direction this this reaction is just as likely happening as the reverse reaction so we could put this in equilibrium we could put this in equilibrium but if that were to happen then what started off as our ketone now looks like this it now looks like this we have a bond to an OHA up to an H group just like this and over here lecture let me draw the rest of it we had our molecule that looked like that but now this electron gets given back to this carbo cation we now have a double bond here between between our between our carbonyl carbon or what was a carbonyl carbon and our alpha carbon so now we have this double bond right over here we have this double bond right over here that hydrogen has been taken via the water and now that is hydronium so let me draw the water or the hydronium so that water it had that one lone pair and then the other lone pair got broken up because it gave one of the electrons to this hydrogen right over here and it went back to being hydronium so what happened here we started with a ketone we started with a ketone and we sometimes we call this the keto form of the molecule and then we ended up with something called the enol form an enol or maybe an e yeah I should say that eknoll or enol form an enol comes from the fact that it is an alkene alkene it is an alkene that is also an alcohol you could even call it an alkene all it has a double bond and on one of the carbons it has a double bond it has an O H group and the whole reason I showed you this mechanism is one just to show you a mechanism that could happen with an aldehyde or a ketone this was a ketone but if this was a hydrogen right here this would have been occurring with an aldehyde but even more this is a pretty common mechanism that you'll see in organic chemistry classes and actually has a lot of functions in biology in general and these two molecules these two molecules this ketone and this enol form these are called tautomers these are called tautomers these are called tautomers and the keto form is actually the much more stable form you'll in a solution you'll you won't see much of the enol form but these can occur it can spontaneously through equilibrium get to the actual enol form and so you could imagine these are tautomers so this mechanism is actually called a tautomerization and these are the keto and enol forms of the tautomers