so we will continue with the mechanisms of electrophilic addition reaction the addition of hydrogen halide to a cc double bond so let's take a look at this next example if our alkenes are unsymmetrically substituted which means the two carbon atoms the two double bonded carbon atoms have different substituents like this case the left one has h and a methyl attached to it the right carbon has two hydrogens the double bond is not symmetrical so in this case when we put H and cl to the double bonded carbon in the addition reaction which carbon should get the H which carbon should get the CL so here are the structures of two potential products in the first case we put H in the middle carbon CL on the terminal carbon in the second case I put CL in the middle carbon h on the terminal carbon so that's two po potential products depending on where the hydrogen and the chlorine goes to the double bonded carbon atoms two different double bonding carbon atoms all right so it was found that the second product the chlorine in the middle that is the major product and the first product when chlorine is attached to a terminal carbon that is the minor product so here I want to introduce the concept of radial selective or radial selectivity so this term refers to the reactions that can proceed in more than one direction but One Direction is is preferred so like the addition of HCL to an unsymmetrical alkenes we can get more than one potential products more than one directions but one is preferred we have a major product and minor ones okay major product is the direction that is preferred by the reaction so that's the definition for radial selectivity so we can call this addition reaction this hydrohalogenation reaction as a radiio selective reaction because we have a major product and a minor product okay the rules that hydrohalogenation follows regarding to the radio selectivity is called MAA nikov Rule and the maaf nikov rule states that in the addition reaction of hydrogen halide to an unsymmetrically substituted alkenes the hydrogen adds to the carbon that has greater number of hydrogens and the hogen adds to the carbon having fewer hydrogen atoms okay so a simplified version here for mov nikov rule H add to the carbon with more hydrogens all right so if you look at the structure of this proping the two double bond carbon the middle one is CH terminal one is ch2 H will go to the carbon with more hydrogens that's why H goes to the terminal carbon chlorine will stay on the carbon with fewer hydrogens a middle carbon or another way to say this is H will go to a less substituted carbon CL will go to a more substituted carbon all right let's take a look at the ma mechanism for the reaction or the magntic background that can be used to explain the mopon C rule so the first step in the mechanism the pi electrons of the double bond will be donated to the hydrogen and HCL Bond breaks then the hydrogen will be attached to one double bonded carbon leaving the other carbon a positive charge so here is the first carbo CA that may form H goes to the middle carbon leaving the positive charge on the terminal carbon or another possibility H goes to the terminal carbon leaving the positive charge on the metal carbon so now let's take a look at the difference between these two carbo cines the first carbo cadine is a primary carbo cine the second carbo is a secondary carbo CA right so we have explained previously regarding the stability of carbo secondary caroon will be more stable than primary Comon and if the carbo canine is more stable it's going to form faster all right so secondary carboon is more stable it will form faster and the major product of the reaction will be from the secondary carbo okay the major product is from the more stable carboca intermediates all right so the chlorine atom or the chlorine ion C minus will be added to the mdle carbon in this secondary carboca okay so this is how we explain the Regal selectivity in the electrophilic addition of HCL to the double bond all right so let's take a look at a few examples will you be able to predict the major product from the following reactions the first one one building react with h BR in acetic acid acetic acid is the solvent the reaction follows the mopon C rule so H goes to the terminal carbon BR to the carbon in the middle of the chin double bonded carbon so here is the structure of the final product two bromo butane next reaction two methyl one proing addition of hbr to it same reaction condition what's the product the major product again the reaction will be radiio selective H goes to the carbon with more hydrogen BR to the carbon with fewer hydrogen and here's the structure of the major product next one it's methyl cycop panting reacting with HCL same reaction condition again H goes to the carbon with more hydrogen CL goes to the carbon with fewer hydrogens okay so in the next exam you will be expecting questions asking you to predict the major products of the reactions next topic that I'm going to cover is related to cocine it's called carotin rearrangement let's take a look at this carbo cadine first so the carbon with the charge is in the middle of the gy and it's a secondary carbo now I'm going to focus on the next carbon to the carboon mainly the one on the left we have a secondary carboon but the carbon on the left is a tertiary carbon right so so a tertiary carbon has the potential to form a tertiary carbo CA correct in this case the next carbon has the potential to form a more stable caroal tertiary over secondary the carboca will re re arrange itself to give the more stable caroa how by moving one group on that tertiary car on that tertiary carbon to the carbo cat in this particular case what will be moved is the hydrogen if we move hydrogen from from that tertiary carbo sorry from that tertiary carbon to the caroa along with the pair of electrons in the CH Bond the carbo now will become ch2 and there will be no charge anymore because hydrogen shift with the par electrons but the carbon on the left now we have a positive charge hydrogen shifted along with the pair of electrons now this carbon is giving away its electron density now it will have the positive charge so as a result a new carboon is for formed and this is a tertiary carboca this process involves a hydride shift the hydrogen with two electrons is called a hydride okay so that's a carotin rearrangement and the driving force for the carboon rearrangement is is the formation of a more stable carbo CA okay a side note here different types of hydrogen containing species H+ is called a proton H with a DOT that's the hydrogen atom or a hydrogen radical and H with two dots that's the hydride because of the different electrons they have these species will behave differently in the reactions let's take a look at another combo Canon rearrangement so here we start with a secondary carbo cine the carbon next to it mainly the one on the left is a quinary carbon it has four other carbons attached to it so in this case the carbon to the left of the caroa also have the potential to form a more stable caroa than a secondary carbo in this particular case we are going to move a methyl group from a quinary carbon to the adjacent carbo and again this shift involves a methyl along with the pair of electrons in that carbon carbon Bond okay so after the methyl shift a new carocon will be formed on the initially quary carbon now it's a tertiary carbon okay so again we are going from a secondary carbo cine to a tertiary carbo in this case so let's take a look at the reaction this is our alken and we want to do an hydrohalogenation addition of HCL to the double bond if you just follow the makov nikov rule you would say Okay H goes to the hydrogen with more Hydro uh H goes to the carbon with more hydrogen terminal carbon CL goes to the carbon with fewer hydrogen so the second carbon all right and uh here is the structure that you would expect to be the major product which follows the makov nikov rule right but it turned out that this is not the major product of the reaction so what is going on here so I'm going to list all the potential products for this reaction structure a here is what we would expect from the marov covs rule right and uh structure B is the minor product right we would expect a is a major B is the minor product but it turned out that c is the major product how does c form compound C here through carboon rearrangement so you can imagine in order to form product a hydrogen goes to the terminal carbon leaving the positive charge on the second second carbon which will be a secondary caroa right and this is the same carboca that I described in the previous slide then that carbo Canon will rearrange to give a tertiary carbo catin and the tertiary carbo catin combines with chloride to give the final product C okay so the major product of the reaction is from carbo rearrangement as a result whenever carboon is involved as the reaction intermediate you will have to consider carbo Cat [Music] rearrangement last example here our electrophilic addition okay addition of HCL to the double bond what is the major product so here are the structure of all the potential products a b and c it was found that c is the major product all right so I want you to draw the mechanism of the reaction showing how the major product C is for and we will check the answer in class