in this video we're going to talk about the microreaction so the first thing we need is a michael donor which is typically a stabilized enolate so let's use a base to remove the alpha hydrogen in the first step and so here we have an enolate that is stabilized by two carbonyl groups and then this is going to react with an alpha beta unsaturated aldehyde here is the alpha carbon and here is the beta carbon now you need to know that the beta carbon and the carbonyl carbon they're both electrophilic and so whenever you have a nucleophile a nucleophile can attack at the beta carbon or at the carbonyl carbon weak bases tend to attack at the beta carbon and strong bases they tend to attack at the carbonyl carbon giving you direct addition whereas a weak base will give you conjugate addition and so in order to get the micro reaction we want this stabilized enolate or weak base to attack at the beta carbon and so that's why it's good that the enolate is between two carbonyl groups because weak bases prefer to attack here now if you want to see why those two carbon atoms are electrophilic here's how you can show it so we know that the carbonyl carbon is electrophilic because if we draw this resonance structure we can put a positive charge on the carbonyl carbon thus proving that it's electrophilic now to show that the beta carbon is electrophilic as well here's what we can do if we draw the resonance structure for that molecule based on those arrows we could put a positive charge on a beta carbon showing that it's electrophilic now let's get back to the reaction so here we have a michael donor it's a stabilized enolate ion and the mycodonor is basically a nucleophile and it's going to react with the michael acceptor which in this example is the alpha beta unsaturated aldehyde the michael acceptor serves as an electrophile and so the carbon with the negative charge is going to attack the beta carbon causing these pi electrons to move to the adjacent bond break in that pi bond and so now let's count the longest chain this is carbon 1 2 3 carbon 3 attacks the beta carbon which we'll call carbon four and so we have a six carbon chain which looks like this on carbon six we have an oxygen with a negative charge and we have a double bond between five and six now on carbon three we have these two carbons so let's put that here and so this is what we now have now in the next step we need to react this with a weak acid so i'm going to use water as an example depending on your solvent it could differ so just keep that in mind as the oxygen bears back down on the double bond it causes the double bond to be nucleophilic except in actually not nucleophilic but more basic rather because it's except in the hydrogen and so we're going to get this product and so this is the product of the micro reaction typically a one five dicarbonyl compound is formed after the microreaction now let's work on another example so let's react this compound with potassium hydroxide and then in the second step we're going to use an alpha beta unsaturated aldehyde and then in the third step let's use water so go ahead and predict the major product for this reaction feel free to pause the video so let's write up a mechanism just like before so in the first step we're going to use the base to remove the alpha hydrogen generating the enolate ion now in the second step we are going to react that with our michael acceptor and so the enolate will attack the beta carbon causing this to move over here breaking the pi bond and so we're going to get this product so we have an oxygen with a negative charge and the double bond and also we have a methyl group on this carbon so you have one two three four carbons that were added and the enolate attacked carbon two so we got to make sure we have the right number of carbon atoms and then in the last step we need to add a hydrogen and so this is the product for the microreaction and the product looks like this once again we have a 1 5 dicarbonyl compound as our product here's a question for you can this enolate ion serve as a micro donor what's going to happen if we react it with an alpha beta unsaturated aldehyde will it attack at the beta carbon or at the carbonyl carbon if it attacks as a beta carbon then that's going to lead to the microreaction if it attacks at the carbonyl carbon it's not going to lead to the microreaction it turns out that this enolate ion is not a very good micro donor now granted it can participate in the micro reaction it could attack the beta carbon however it prefers to attack the carbonyl carbon because this is a relatively strong base and so these two sites are in competition therefore the yield for the micro reaction is not good with this type of enely ion whereas if you have a more stable all right this computer's having issues now if you have a more stable enolate ion this base is not as strong as this one it's actually much weaker and so this will prefer to attack at the beta carbon rather than at the carbonyl carbon and to understand why you can analyze the pka of the conjugate acid so the pka of the alpha hydrogen of a diketone is about nine and the pka of acetone is around 20 and the pka of water is 15.7 the stronger the conjugate acid the weaker the conjugate base the strongest acid is the one of the lowest pka so therefore this is going to be the weakest conjugate base so the strongest conjugate base is the one of the weakest acid or the highest pka so this enolate ion based on the pka values is stronger than hydroxide and hydroxide is a stronger base than the enolate ion that's flanked by two carbonyl groups so we know hydroxide is considered to be a strong base so therefore this is definitely a strong base as well and the enolate ion between two carbonyl groups that's considered to be a weak base and so this is a very good michael donor now let's go back to this reaction so right now this is not going to give us a good yield in terms of the mycologist reaction this ion will prefer to attack at the carbonyl carbon rather than at the beta carbon so the yields will be low for the michael addition product however we can increase those yields even using this enola ion by adjusting the michael acceptor so basically what we need to do is make the beta carbon more accessible towards a nucleophilic attack whereas the carbonyl carbon we want to add some groups to it and make it less accessible so the first thing we could do is instead of using an aldehyde we can use a ketone and ketones are less reactive than aldehydes at the carbonyl group because of the ch3 so this ch3 reduces the accessibility of the nucleophile to the carbonyl group it provides steric hindrance and also it's an electron donating group so it donates electron density to the carbonyl carbon making it less electrophilic and so by using a ketone and alpha beta unsaturated ketone as opposed to an aldehyde you can increase the yield of the microaddition reaction so now it's easier for the nucleophile to attack at the beta carbon than at the carbonyl carbon it could still attack here though by the way because this ketone is not it's not too sterically hindered so it can attack at both we can get a mixture of products however we can increase the yield further if we make the ketone even less accessible let's say if we add if there's a tert-butyl group instead so now it's a lot harder for the nucleophile to approach the carbonyl carbon and so in this case we could say that this will now be a good microreaction even though we have a strong base the best place to attack will be the beta carbon giving us the michael addition product so just keep this in mind a good michael donor is a weak base if you have a strong base it's not a very good micro donor but it can participate in a micro reaction if you use an alpha beta unsaturated keystone that is sterically hindered at the carbonyl site so just keep that in mind now let's work on one more example so here we have nitro ethane and we're going to react it with potassium hydroxide followed by a michael acceptor with a nitrile functional group and then the last step will be h2o so go ahead and predict the major product for this reaction now the alpha hydrogen of nitroethane is relatively acidic the pka is about 9 as well so therefore this is going to be a good micro donor now the first thing we need to do is we need to take off the hydrogen and so let's use hydroxide to do that so the nitro group looks like this and as you can see the carbon with the negative charge is stabilized by the nitro group we can basically put the negative charge on the oxygen if we want to and so this base is a weak base because the negative charge is stabilized by this oxygen atom so now that we have a good michael donor let's react it with the michael acceptor so the carbon with the negative charge will attack the beta carbon pushing the pi electrons here causing this pi bond to break let's call this carbon 1 carbon 2 which connects the carbon 3 and this is 4 and 5. so this is carbon three four and then five is the carbon atom which now has a double bond and the nitrogen atom has two lone pairs and a negative charge and we also have another double bond here which i think i need to redraw it better now the last step is to react with water so this lone pair is going to reform the nitrile group causing this pi bond to break except in hydrogen from water and so now we have our final product so we have a total of five carbons this is three four and then the fifth carbon is part of the nitrile group and then attached to carbon 2 we have the nitro group and so this is the major product of the micro reaction you