Leaving Group Conversions Summary

So here's what I hope will be a hopeful cheat sheet for you guys to compare the different types of alcohols you could start with and the stereo chemistry that you'll get at the end, all of these reactions remember are going to convert alcohols to good leaving groups but they are going to proceed with different stereo chemistry so because this section has so much to do with stereo chemistry that's why I made this entire axis all about stereo chem, alright? So let's go ahead and start off with what if we want a good leaving group we want to convert alcohol to a good leaving group you want the end product to be racemic, OK? Well if that's the case then we could start with a secondary or tertiary alcohol and we could use Hx in an SN1 reaction, OK? Hx is the only reaction in SN1 that gives us 2 enantiomers that gives us a combination of products, OK? Now you might be wondering well Johnny why is it greyed out here? Why can't I also use that on a primary alcohol, OK? Well remember because primary alcohols don't form good Carbocation and in order to make a racemic mixture you need a good carbocation So I'm just going to write here can't make Carbocation and if you can't make the Carbocation that means you are going to do an SN2 mechanism not an SN1 so that's why it's greyed out, OK? Now one more thing I just want to add remember that what happens in the case of HCL? Can I also just use HCL by itself? No, remember we use or the Lucas reagent HCL over zinc and 2 chorines, the Lewis acid catalyst, OK? Cool so let's keep going what if IÕm starting with alcohol and I want to get inversion of configuration at the end, I don't really care what the leaving group is as long as it's inverted, OK? Well if it's primary alcohol then I can use Hx or SOCL2 and PVR3 so just you know SOCL2 and PVR3 are always good options for inversion, OK? Because of the fact that you get a backside attack every time, why did I only put the HX SN2 here? Why did I not put it in the secondary position.? Because if you guys remember HX will actually if you do it with a secondary it's actually going to wind up giving you an SN1 reaction so that's why we can't use it in the secondary position we can only use it in the primary position if you have a primary Alkyl Halide you will get an SN2, you will inversion but if that secondary remember you make your carbocation again and you would form a racemic mixture, OK? You might be wondering well Johnny why is this greyed out? Why can't I just do an inversion of configuration on a tertiary as well? Why can't I use SOCL2? Because remember you can't do a back side attack on a tertiary it's too crowded, OK? So I'm just going to put here bad backside since it's a bad backside I can never do an inversion of configuration on a tertiary, cool?

Alright so lastly what if I want retention of configuration? I don't really care what the leading group is as long as it's good and I don't want it to be alcohol obviously, well anytime you want retention of configuration you're going to use Sulfonyl chlorides to turn your alcohol into a Solphonate Ester, OK? This one's really easy because it doesn't matter what degree your alcohol is, it always works primary, secondary, tertiary it's always the same thing you're going to wind up getting a Solphonate Ester and it's that easy and then later on you can react it, OK? So hopefully that helps us to kind of organize the different ways that we can convert alcohol to good leaving groups, professors love to test on stereo chemistry here and that's why I really emphasized knowing the differences in stereo chemistry between these options, alright? So I hope that made sense to you guys let's go ahead and move on.