I shout out and thank you to my teaching colleague just trying to make the best videos on the internet that explained the data not just transmit the information to you okay listen 20.1 types of organic reactions first of all sn1 sn2 reactions if you have a careful look here that substitution nucleophilic that is a one step and that's a two step of order of reaction so going through the solvent terminology here you will need to know what sort of solvents they are they are all polar solvents by the way because if they're not polar they went dissolve in water and so the reaction won't occur can't work in oil so you need to take polar each time you then need to work out whether it's protic or a protein you will need to learn some of those so the protec the acetone the propound propanone so that's a key time to learn that one as a non and a protic it doesn't release protons all the solvent and water or ethanol are able to release hydrogen's from their bonds so this is a summary for sn2 reactions I think it's best going over this in the actual slide if you look at the video here you'll see that there is no steric hindrance here from the hydrogen atoms so here we can see that the lone pair of electrons comes in from the opposite side it repels the hydrogen's you can see from the data booklet on covalent bond lengths that the carbon chlorine bond is longer than the carbon oxygen bond so there's a shorter bond here so as you can see when the oxygen bonds it's a shorter bond it's a stronger bond that has a greater effect pushing out the hydrogen's and so the chlorine will then the hydrogen's will then push off the chlorine I'm going to go in this in more detail because the mechanism needs to be known as I've said if you look at your data booklet you'll find that this bond here bond enthalpy is much weaker than this one here so that's how you know it's the H binding not the seal binding not the other way around make sure you do this at 180 degrees that's something new in the last year you really need to draw this electron all these electrons coming in and the electrons do the movement that then pushes these out so these are all worth marks here must have the square brackets with the negative charge on the outside and do the dashed line to show that's now shared so this is a transition state so it's not stable it just happens for a momentary point in time and then it jumps over into this here and this the chlorine pops off this is completely dependent on two things the concentration of this and the concentration of this that's why it's two so the order of reaction is two so if I drew that out in the previous slide I'd have both the halo al elahh generic a nucleophile there so that's why it's a - it's a nucleophile it's a negative so that's where the end comes in here and you need an ape and a protic solvent because if you have a protic solvent and then you will have water breaking off into these things for instance and that will then be allowed to react so that's the most important thing with those with the sn2 s so it's a polar a protic solvent and it's also important to go back to your terminology from your earlier units so it's unable to form hydrogen bonds and that will help stop the nucleophile binding to it here and it'll also stop the formation of other species that will interact with the reaction you can see from this little clip here you can see the lone pair of electrons here there's no way there is like with sn2 to come in from the other side because of the steric hindrance from the CH the methyl groups and so what you need to do is wait for the chlorine to pop off and then one that once that's happened you can see it takes the lone pair with it it creates a carbo-cation that allows the lone pair of electrons from the hydroxyl group to come in and bind sn1 reaction T now the key with sn1 is it's completely dependent here on this this very strange thing here this carbo cation for me because that is really the massive inhibition here it's only one thing so this is it just depends on how much there is of this so that's just sn1 that itself is stable because an intermediate not a transition state the solvent here is a protic solvent because in this particular case it will do some interfering but the most important thing is trying to get this stable so it actually occurs and so the reaction actually works which you're going to talk about carbo cation positive induction is what we use to describe how this ch3 groups help support this positive now if they were hydrogen's they would they would have no interest in this being positive that would not help their bonds here so the ch3 groups are much better at supporting the carbon being positive there let's go back to this sn1 reaction so you will have here this carbo cation forming and then you may need to make sure you've done this here this double arrow that's key I would add that as well and definitely the positive needs to be there you then must draw these electrons here attacking the carbo cation I would just play it safe and at the very end still show the chlorine product as well coming off for the periodic table you can see that fluorine is the most electronegative and then it's chlorine bromine iodine so the carbon bonds here this would be more electronegative this would be more electropositive so you would expect the d nucleophilic attack here from an electrophile would be able to be more effective and so that breed of reaction would ink would be greatest for for the fluorines however if you look at the bonds here you'll actually see the carbon fluorine bond is actually the strongest and at the flooring and the halogen alkane bonds actually get weaker down the periodic table so that how that means that further down the periodic table these bonds actually break easier and so this has a more significant effect so the rate actually increases as you go down as you go up the periodic table now that effect to remember on the mechanism tertiary is just sn1 primary is sn2 secondary can be both sn1 and sn2 electrophilic addition reactions we've covered this before but this is high level now so you need to know the mechanism so the double arrow here and the double arrow here gives you heterolytic fission that then creates this carbo cation and the nucleophile can then come in and react same story here just make sure you draw in the correct double arrows here it's also good to write the dipoles here put a negative and the arrows here you may be given a double bond in this sense here and you need to work out whether the hydrogen goes here the hydrogen goes here you need to remember positive induction here so if you have a look here again we said that the the H pluses don't have really much as good an effect as stabilizing this carbo cation as the side groups do so if you look here you'll find that the carbo cation here with the positive induction would be much better than just here so we've sort of reversed sort of the way to say this and so the general rule have a look and draw it out and see where the positive carbo cation is to work out where it goes and so basically the ones the car with the most hydrogen gets the other hydrogen is the basic rule so if you have a look here where is it going to go this one has the most hydrogens on it so you're going to put the hydrogen on here and so you're going to get to bromo propionate propane rather than one bromo propane electrophilic substitution reactions now now you might not know that sulfuric acid is a stronger acid the KA is actually a thousand whereas the KA for nitric acid is only forty three so what I like to do is I picture the sulfuric acid in the nitric acid look at the ability of the oxygens to hold on to the hydrogen and if you look at the ratios you will see from this little clip that the ratios of the nitric acid is much better so it has the greater ability to hold on to the hydrogen so if that's how you're going to remember when you put nitric acid and sulfuric acid together it's actually going to be the nitric acid that's going to be able to grab on to the extra hydrogen so here we see that sulfuric acid is lost out here and it's taken hydrogen and not the nitric acid as being able to grab the hydrogen that's then created a stable compound the water that pops off and here you have your nitronium iron so here we have our electrophile once we have our electrophile we can actually heat this up this is actually a more stable bond but the heat disabled destabilizes the electron structure and say that allows this nitrogen to come in and replace the hydrogen and so that allows this nitronium mine to come in and replace the hydrogen reduction reactions now now to remember these particular catalysts that cause the reduction of these compounds here I use the periodic table so using the periodic table here we know we're reducing them so we need the hydride which is the h minus ion and so we have here lithium aluminium hydride which comes first so that's used for the primary alcohols and then sodium boron hydride so it's just a cross over here and that's one there one pluses and there three pluses so you would expect here that the hydride the before of them so there we go living at el-amin lithium aluminium hydride the four hydrogen's so that's how you remember the catalysts now this is primary this is actually the stronger agent this is the act this is actually the stronger reducing agent and as we saw in the product table this comes first so that's the primary och alcohols here that that have worked on created and here we have the secondary so you just work backwards from your oxidation of alcohols put the hydride in there because you're not oxidized in your juicing and I just showed you how to remember the catalysts the syllabus was unclear about whether the mechanism needs to be known and in truth finding these questions on these sort of things it's really getting quite obscure and it's really getting to the memorization stage so if you have time memorize these otherwise I would leave them if you see that this is created you can sometimes guess where it's coming from because you will need to get a h2o often to how to do that it makes sense because this is quite a common grouping here and acids or bases are often used catalyze this here I would probably memorize this one first before we memorize the second one so how would you get that if you are asked to get this you would think well how am I going to the hydrogen's I'll add some sort of acid in this case it happens to be hydrochloric acid 10 so that goes into the memorization bank