in the next section we're going to now combine patterns of Arrow pushing so in section 6.8 we looked at the four uh individual patterns that result in uh movement of electrons when we have reaction mechanisms occurring now we're going to combine these uh to kind of see uh movement of electrons throughout a whole reaction so you can see in this example down here um one or more of the four patterns will occur in any given reaction so this example here first we see a proton transfer so you see that characteristic two arrows used and um this first arrow is pointing to a proton and that has um moved right from our um our reactant after grabs a proton we see our new species here so that is indicative of a proton transfer the two arrows and our product after the first step now has that proton attached um then we have in our second pattern here we show loss of a leaving group so that's a single Arrow uh in this Arrow pushing pattern here and we see over our reaction uh Arrow here that there's a negative H2O so that's a good sign that um something's going to be leaving if we have this minus sign here above our Arrow the next Arrow pushing pattern that we see is the carbocation rearrangement so we have a again a secondary carbocation here and if possible if a methyl methide shift or a hydride shift can occur to stabilize this carbocation it will so not only um do we see right this methide right down the on the next carbon there but we see in our product after this reaction we see this carbocation rearrangement to a tertiary so more stable carbocation and we have our electrophilic site now this uh carbocation and we have a nucleophile here our bromide ion so now we can see our last um Arrow pushing pattern shown with this nucleophilic attack so um often times we can see two patterns in a single mechanistic step so that's shown down here where not only do we have um right our nucleophile here so our nucleophilic attack occurs with this first Arrow but then we also see so this is Arrow one nucleophilic Tack and then our second Arrow shown here um shows us the loss of a leaving GR group right so there's our alcohol after the nucleophilic attack and our leaving group right our LG over here is our chloride ion so these happen simultaneously so let's take a look at um this example here so again um we have our curved Arrow which starts at a pair of electrons so on our moon pair here and the head of the arrow goes to this electrophilic site uh so we saw through induction that um when we have an electron withdrawing group this could be uh right a partial site a partial positive charge because of this electron withdrawing group so that's where our nucleophilic attack will happen at this electrophilic Center and that causes in the second Arrow um the movement of the electrons in this bond to move to our chloride ion here and what we C is our product after our nucleophilic attack and our loss of leaving group on the bottom here um they show you an example of what not to do not to start your arrow here but rather at this site here as we saw above so the Arrow Head um should end up on the chlorine the same but the arrow tail should start um specifically on the bond that's breaking with our loss of leaving group so don't make that mistake um you may see questions that show you both uh right as a multiple choice answer for example so be careful so our next example um we're going to look at uh when we have a formation of a bond right so we have our bond forming between this um lone pair and this electrophilic center with our nucleophilic attack and then we have again in the second Arrow we see our loss of leaving group and the electrons shifting to our chloride ion um one thing to be careful or note when you are um doing this type of uh Arrow pushing um you cannot violate the octet rule so in this case um we cannot have uh just one Arrow one uh Arrow pushing pattern shown here with the nucleophilic attack right because this would um oh sorry over here this would violate the octet Ru because we already have four bonds to that carbon so what we have to show is this second Arrow over here where the electrons are leaving in this Bond and going to the chloride atom so that's why we need this loss of leading group as well because we do not we're not able to violate the octet rule carbon cannot have um an expanded octet because it's only a second period atom it's only in the second row so any of these uh curved arrows um should be you know describing one of these four patterns discussed so far um so we saw nucleophilic attack we saw loss of leaving group um now the arrow uh shown below here um they say is unreasonable it violates the octet and it also doesn't match any of the four patterns that we saw before so theoretically right you can move electrons from one carbon to another that are involved in a pi Bond but um we can't violate the octat um and we also can't you know move electrons um you know three or four carbons down they can only move to an adjacent carbon atom so that's everything uh as far as our discussion on combining these Arrow pushing patterns uh we'll continue with our next section during our uh next lecture