laya here from labor sicom and in this video I will take you through the e1 reaction rate and mechanism the e and e one stands for elimination and the one tells you that this is a uni molecular reaction so let's break this down elimination means to remove something or to get rid of something and specifically we're getting rid of a beta hydrogen and a leaving group so this reaction should actually be called beta elimination Union molecular does not tell you that it's a one-step reaction but instead tells you that it's a first-order reaction and can actually involve two or more steps so let's see what happens in a beta elimination reaction the reaction begins when the leaving group breaks away from the parent chain dissolving somewhere in solution and leaving you with a positive charge on the parent chain let's classify the carbons on this molecule the carpet that first held the leaving group and now has a positive charge is considered the Alpha or the first carbon and any carbon directly attached to the alpha carbon can be considered carbon number two or simply the beta carbon on this molecule we have three equivalent beta carbons each of which has three hydrogen's which we'll call beta hydrogen's in the final step of this reaction a base will use its lone pair of electrons to grab one of the beta hydrogen's but only the nucleus and not the bonding electrons when the hydrogen is grabbed the electrons that bound it to the carbon will collapse towards that positive charge forming a PI bond between the Alpha and the beta carbon the final product in an e1 reaction has a PI bond between the alpha and beta carbon where we eliminated the beta hydrogen and the leaving group an important thing to recognize here is that even though the leaving group is departing by itself this is still considered a very slow step because you're taking a neutral molecule breaking something off it resulting in a positive product this is such a slow step it's actually the rate determining step of this reaction let's take a look at the kinetics of an e1 reaction the rate of an e1 reaction is equal to some constant K that you don't have to worry about times the concentration of the molecule involved in the rate-determining step meaning the alkyl chain the final step of the reaction where the base grabs a hydrogen that happened so quickly that the speed is negligible compared to how slowly that carbo cation forms and so the base is not looked at when determining the rate of an e1 reaction since only one molecule shows up in the rate law we have a first-order reaction and this gives us the one in our II 1 or unis molecular reaction this tells you that if you double the concentration of your starting molecule the reaction rate will double if you triple the concentration the reaction rate will triple but if you double the concentration of the base nothing happens to the rate of the reaction because the concentration of the base doesn't do anything to the speed of this reaction let's look at the mechanism for the e1 reaction by analyzing what happens when to bromo to ethyl pentane reacts with h2 so4 in water and heat by using the four part checklist that i analyzed all substitution and elimination reactions for detailed videos on how to analyze each aspect of this checklist visit my website layer for sicom slash substitution - elimination will begin with the alkyl chain specifically looking at both the Alpha and the beta carbons the alpha carbon which holds the leaving group is a tertiary carbon which tells you that you can form a stable carbo cation and therefore a 1 type reaction meaning sn1 or e1 can take place while sn2 cannot take place with a tertiary leaving group we can't rule out the e2 reaction for elimination reactions you also want to look at your beta carbons to ensure that you have hydrogen's that can be removed for the reaction to proceed next we look at the leaving group bromine which forms a stable anion solution is a good leaving group that can depart by itself allowing both a 1 type meaning s o1 e 1 or a 2 type sn2 e2 to take place next we look at the attacking molecule since this is elimination we're not looking for a nucleophile but rather looking for a base the problem is we don't seem to have one in fact h2so4 is an acid so how can we have a base in this solution whenever it appears that you don't have a reactor molecule present look for the concept of solvolysis where the solvent itself acts as the attacking molecule h2o in addition to being the solvent is also a weak base because it's neutral it's not strong enough to forcibly kick out a leaving group and will have to resort to the one type reaction meaning sn1 or e1 where it waits for the leaving group to depart before attacking the molecule and lastly we have h2o as a solvent which is polar protic and that means it can stabilize any charges that form in solution and will therefore also favor our one type reactions you will often see competition between your sn1 and e1 reaction so don't automatically say that only one or only the other can happen in this case we can have both sn1 and e1 take place however there are two things I want to point out the first is that we have the triangle which represents heat and heat tends to favor elimination over substitution the second thing since this is a new one video I'm only going to show the mechanism for e 1 but keep in mind we will have some substituted products forming as well the e1 reaction starts out when the leaving group grabs the two bonding electrons and breaks away from the carbon molecule dissolving somewhere in solution the carbon that used to hold the leaving group is now deficient and gets a formal charge of plus 1 since this is a tertiary carbo cation it is stable in solution and don't forget is also surrounded by the polar protic water molecules stabilizing it even further we can show the BR minus as off somewhere in solution and now let's look at the beta carbons the carbon holding the carbo cation is alpha and any carbon directly attached to that is considered beta on this molecule we have 3 beta carbons and since the molecule is perfectly symmetrical so are the beta carbons the carbo cation is your alpha carbon and any carbon directly attached to that is your beta carbon in line structure you typically do not show hydrogen's but because we're doing a beta elimination I want to show you all the hydrogen's and realize that they're all equivalent given that this molecule is perfectly symmetrical because every beta hydrogen is equivalent I can choose one at random to proceed with the reaction recall that water is a polar protic solvent meaning we have a partial negative oxygen and two partially positive hydrogen atoms water will reach out with the lone pair on the partially negative oxygen to grab one of the beta hydrogen the two electrons that hold the hydrogen to the carbon will break away from the hydrogen and collapse towards that positive alpha carbon the resulting molecule now has a double bond between the alpha carbon and the beta carbon where the elimination took place we also have a positive hydronium in solution which balances the BR minus that departed in the first step a quick charge analysis shows us a neutral starting molecule a negative bromine and a carbo cation for a net charge of zero at the intermediate level and a negative bromine and positive hydronium for a net charge of zero and the products be sure to join me in part two of this series where we analyze the products of an e1 reaction based on zaitsev's rules and the stability of substituted alkenes you can also find my entire substitution and elimination series on my website layer four sicom slash substitution - 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