so let's take a look at the following example in which our goal is to determine the absolute configuration of the new stereogenic carbon carbon number one that is formed in Alpha and beta animers of D glucopyranose so let's begin by looking at our straight chain glucose and its ring counterpart so when we have our D glucose in its straight chain form we basically have a molecule that looks some like this we have six carbons carbon number 1 2 3 4 5 and six now the D part of the D glucose implies that the hydroxy group that will act as the nucleophile this group here basically points to the right and not to the left now if we had L glucose this hydroxy group would point in the opposite direction it would point to the left side now notice on the straight chain D glucose we have only four stereogenic carbons so carbon number two 3 four and five the carbons that contain the asterisk next to them are basically the stereogenic carbons they contain four different groups attached to them the first carbon and the last carbon are not stereogenic now when our intr molecular nucleophilic reaction takes place and this hydroxide acts as the as our nucleophile it can basically attack this carbon either from the top or from the bottom if it attacks from the bottom we form the beta D glucopyranose if it attacks from the top we form the alpha D glucopyranose now the difference the main difference between these two molecules is the orientation of the hydroxide group that is attached to carbon number one so on this molecule this is our first carbon second carbon third carbon fourth carbon fifth carbon and this is our sixth carbon so carbon number one is this carbon here carbon number two is this carbon here three four and five as well as six so when this oxygen acts as a nucleophile forms a bond with this carbon that's basically this Bond here eventually this oxygen here is protonated to form this hydroxy group and this oxygen is deprotonated to form this oxygen here that is bonded to our two carbon atoms now notice in the straight chain case this carbon of the carbonal group was not a stereogenic carbon because we only contained three groups attached to our carbon but this carbon carbon number one that is formed when we form the Alpha and beta animer this carbon does become a stereogenic carbon we have one group two group three group and four groups so in this case the straight chain form we had only four stereogenic carbons but now we have 1 2 3 4 five stereogenic carbons attached to our molecule now the question that we want to answer in this lecture is what is the absolute configuration of this new stereogenic carbon for the beta animer as well as for our Alpha animer whatever it is for the beta animer it should be the opposite for our Alpha animer and we'll see exactly that so let's begin with our beta case so whenever we determine the absolute configuration we have to determine the four different group so we have to label them from the least to the greatest where four is the the least and one is the greatest so let's use I guess purple to designate our numbers so let's begin with the least the least is obviously number four it's this H atom it it is given the least priority now what about the greatest priority which atom or which group gets the greatest well in the first case if we go this way we have an oxygen if we go this way we have a carbon if we go this way we have an oxygen so an oxygen is heavier than carbon so the oxygen wins out so it's either this oxygen or this oxygen here to determine which one it is we have to go to the next atom across in this case we have the oxygen followed by the H in this case we have the oxygen followed by a carbon so because a carbon is heavier than H this gets priority number one while this gets priority number two and so because this has a four priority this must have a third priority so our molecule basically looks something like this now this carbon bond is coming out of the board while this is going into the board so if we look at our molecule let's suppose we're looking at our molecule this way if we're looking at it this way then these two groups are pointing out of the board while these two groups are pointing into the board so let's draw this carbon as our Center carbon so this is our stereogenic carbon so we have our molecule o that points coming out of this way we have our other molecule the H which which coming which is also coming out of the board going this way and we have the other two groups which basically Point into the board we have our let's say we're looking at it this way uh so this is our uh oxygen and this is basically our carbon and the rest so this contains a priority of number two this contains a priority of number one this contains a four and this contains a three so basically we want to orient this in such a way so that the fourth priority points into the board so that we can't actually see it so basically what we do is we rotate it in such a way so that this H goes into the board and if we rotate it basically if we pull on this this way until this points all the way into the board we get the following pictures so we have our o um we have our o on this side and our Carbon on this side so we have a priority of one will be here we're pulling this downward so this is two and this is three so basically we want to go from 1 to three so we go in this direction and this is our clockwise so that means this is the r absolute configuration so this beta D glucopyranose contains the first stereogenic carbon that is our absolute configuration and because the two groups are switched in this case the alpha must contain the S configuration and let's make sure that's true so let's take a look uh looking at our molecule this way so this is labeled as basically four this is labeled as one this is labeled as three and this is labeled as two so now we're looking at it this way so when we look at it that way we basically get the following Di diagram so looking at it this way these two basically come out of the board these two go into the board so we have a molecule that looks something like this we have our H atom so we have the fourth here we have our two here we have our one here and we have our three here so now we basically want to orient it going this way so now when we Orient it when we pull this up we basically contain we have our two pointing this way we have our three pointing this way and our one pointing this way so now if we follow one two 3 pattern now it's going to go in a counterclockwise Direction so this will be our s absolute configuration so our beta for our glucose molecule the beta animer contains this first theogenic carbon that contains our absolute config configuration while the alpha anomer contains the S absolute configuration on that new stereogenic carbon carbon number one