marconico's Rule and anti-markconico's Rule firstly let me teach you some important Concepts like understanding Pi electrons let's consider this alkene we know that it contains double bond which has pi electrons these Pi electrons are Loosely bonded I mean if we bring any electrophile like positive hydrogen ion it can easily attack on the pi electrons because the pi electrons are Loosely bonded secondly understanding symmetrical and unsymmetrical alkenes for example consider these two alkenes and this alkene we can see that this is the double bond at the left hand side of the double bond there are CH and ch3 while at the right hand side of the double bond there are also CH and ch3 now at both sides of the double bond there are same species we call such alkenes as symmetrical alkenes on the other hand and this alkene at the left hand side there are CH and ch3 while at the right hand side there is only ch2 hence this is an unsymmetrical alkene thirdly understanding the stability of carbocations let's consider these carbocations this is the first degree carbocation because this positive carbon is attached to only one carbon this is the second degree carbocation because this positive carbon is attached to two other carbon atoms this is the third degree carbocation because this positive carbon is attached to three other carbon atoms remember that third degree carbocation is more stable than 2 degree carbocation and two degree carbocation is more stable than first degree carbocation it is because third degree carbocation has more positive inductive effect lastly understanding the hydrogen halides like hydrogen iodide hydrogen bromide hydrogen chloride and hydrogen fluoride remember that this is the order of reactivity of hydrogen halides also remember that hydrogen iodide is the most reactive because it easily breaks while hydrogen fluoride is the least reactive because we need high energy to break the bond of hydrogen fluoride and marconico's rule we usually take hydrogen bromide when we break the bond of hydrogen bromide we get positive hydrogen and negative bromine the snotted down all these important points now what is marconico's Rule well remember that this rule is only used for unsymmetrical alkenes now let's consider this propene which is unsymmetrical alkene I add hydrogen bromide to it and no other reagent is added to it then the bond between hydrogen bromide breaks we get hydrogen ion and bromine iron we have already learned that this double bond contains Pi electrons which are Loosely bonded no hydrogen ion will attack on the second carbon and bromine will attack on this first carbon we get ch3 CH this positive hydrogen is added to it ch2 and this negative bromine is added to it we get one bromo pro pen Ally there is another possibility this positive hydrogen May attack on this first carbon and this negative bromine May attack on the second carbon we get ch3 CH this negative bromine is 80 to 8. ch2 and this positive hydrogen is added to it we get two bromo propane now listen carefully here is a big problem I mean serious problem which product will I get one bromo propane are two bromo propane after the reaction well here comes the Marconi cow Baba he states that the negative part of halogen acid is attached to the carbon having less hydrogen atoms in the double bond let me repeat it the negative part of halogen acid is attached to the carbon having less hydrogen atoms and the double bond now we can see that in this double bond this carbon has one hydrogen atom well this carbon has two hydrogen atoms now this negative bromine will attack on this carbon because it has less hydrogen atoms let me repeat it this negative bromine will attack on this carbon because it has less hydrogen atoms well this positive hydrogen will attack on this carbon hence we get two bromo propane not one bromopropan or we say this is Major product and this is minor product to summarize this whole concept merconic of rules state that negative part of acid halogen like negative bromine is attached to the carbon having less number of hydrogen just note it down all these important points now let me teach you the mechanism of marconico's rule well I teach this mechanism in three easy steps in the first step I take hydrogen bromide we know that when the bond breaks between them we get positive hydrogen and negative bromine and the Second Step I Take unsymmetrical alkene like propene and I write it two times now there is possibility that these Pi electrons will shift towards first carbon hence negative charge appears on 8 and positive charge appears on second carbon here I take this positive hydrogen of halogen acid we know that this positive hydrogen will attack on this negative carbon we get ch3 CH positive charge and ch3 this is second degree carbocation because this positive carbon is attached to two other carbon atoms secondly there is another possibility that these spy electrons will shift towards second carbon hence negative charge appears on it and positive charge appears on the first carbon now I bring here this positive hydrogen of halogen acid we know that this positive hydrogen will attack on this negative carbon we get ch3ch2 ch2 positive charge this is first degree carbocation because this positive carbon is attached to only one carbon atom now let me ask you on which carbocation well this negative bromine attack can you guess the answer well we already learned that second degree carbocation is more stable than first degree carbocation hence this negative brominewell attack on the second degree carbocation in the third step I take this second degree carbocation and I place it here secondly I take this negative bromine of acetylogen and I place it here we know that this negative bromine will attack on this positive carbon we get ch3ch this negative bromine is attached to it and ch3 this is two bromo propane and it is the major product thus this is the complete mechanism of marconico's rule finally let me teach you anti-markconicles rule remember that it is also known as peroxide effect the anti-markconicles rule is observed only in hydrogen bromide it cannot be seen in hydrogen iodide hydrogen chloride and hydrogen fluoride now consider propene and hydrogen bromide this time I add reagent to it like benzoyl peroxide according to the marconico's rule the negative bromine is attached to the second carbon because it has less number of hydrogen and the positive hydrogen is attached to First carbon but wait a minute an anti-markconicles rule the negative bromine is attached to the first carbon and the hydrogen is attached to the second carbon as a result we get one bromopropan it is the major product just remember that an antimaconicles rule negative bromine is attached to the first carbon and we get one bromo propane now what about the mechanism of anti-markconicles rule well I follow four steps for its mechanism now in the first step I take benzoyl peroxide this is the benzoyl part peroxide part and benzoyl part now this oxygen will draw its own electron and this oxygen also withdraw its own electron and the bond breaks we call such type of bone breaking as homolytic cleavage now there are two benzoyl part as a result we get to free radicals secondly here homolytic cleavage of bond also occurs we get phenyl free radical and carbon dioxide gas similarly here homolytically which of bond occurs we get phenyl free radical and carbon dioxide gas in the Second Step I Take This free radical of phenyl and I place it here I add hydrogen bromide to 8. now the bond of hydrogen bromide also breaks and we call it homolytic cleavage the phenyl radical will gain this free radical of hydrogen we get Benzene plus this free radical of bromine and the Third Step I Take propene No homolytic cleavage of this Bond occurred we get these two free radicals this one is known as 2 degree free radical because its carbon is attached to two other carbon atoms while this one is known as one degree free radical because its carbon is attached to only one carbon atom remember that 2 degree free radical is more stable than one degree free radical now listen carefully the free radical of bromine will attack on this second degree free radical because it is more stable let me repeat it the free radical of bromine will attack on this second degree free radical because it is more stable hence I write 2 degree free radical plus bromine I get ch3ch dot ch2 bromine in the fourth step I take hydrogen bromide and its Bond cleave homolytically I take this 2 degree free radical and I place it here this free radical of hydrogen is attached to this carbon as a result I get one bromopropane which is the major product hence this is the complete mechanism of anti-markconicles rule I hope that you have learned all these important Concepts