let's take a look at another example now once again the first thing we have to do is identify the longest carbon chain in the molecule here it's still pretty simple, it's just gonna be this one in the horizontal plane. now it may not always be so depending on how tricky your professor is you may want to investigate as to whether there is another direction that is going to give you a longer carbon chain, so definitely be careful, make sure you are selecting the longest carbon chain possible. so now we have identified the long as carbon chain we must decide which direction to number it left to right or right to left, again we're gonna choose the direction that gives a substituent occurring soonest, in this case we're gonna have to number right to left because a substituent occurs on the second carbon from the right whereas from the left he would occur on the 3rd so we're gonna number this right to left and we're gonna see that there are therefore two alkyl substituents. we have a two carbon substituent here and one carbon substituent here so that means that this molecule overall is a heptane and there is a methyl substituent and this two carbon substituent is an ethyl substituent. so we know that this is a heptane but now separately from the algorithm that we use to number the molecule a different algorithm is going to be used to figure out in what order we name all the parts of the molecule we are gonna have to list these in alphabetical order so ethyl starts with E methyl starts with M and for that reason alone we're going to list the ethyl group first on the carbon that it occurs so that is 5-ethyl 2-methylheptane so once again this is a completely arbitrary rule but if we all follow it we will be able to come up with the same name for the molecule E before M, ethyl before methyl just as a point of convention in between words and numbers we will have a hyphen and later we will see that in between numbers there is a comma let's look at a slightly trickier example once again, the first thing we're going to do is identify the longest carbon chain in the case that we have a substituent occurring at the same position regardless of whether we begin numbering from the left or the right we are going to give priority to the substituent that occurs soonest alphabetically so in this case because they are both alkyl substituents they have the same priority. later we will see other types of substituents that take priority over alkyl but in this case we're just gonna go with alphabeticity so we have a methyl and we have an ethyl occurring on carbon 3 regardless of whether we start from the left to the right but ethyl before methyl alphabetically so we will number right to left now we identified that we have a methyl group on carbon 5 a methyl group on carbon 4 and an ethyl group on carbon 3 if it is the case that we have multiple substituents of the same type on a given molecule we're going to list them simultaneously with a prefix indicating how many of them there are but that prefix will not be taken into account for alphabeticity so ethyl is before methyl so we will write that first so we have 3-ethyl, and then we are going to say 4,5-dimethyl heptane so the point is that we have identified that there are two identical methyl groups so we want to list them at the same time but with the prefix "di" indicating that there are two of them and then the numbers 4 and 5 separated by a comma indicating that they occur on carbons 4 and 5 in the molecule however it remains the case that E before M in other words these prefixes which would be di, tri, or tetra are not taken into account for the alphabetically. now let's take a look at a couple of groups that have names that are common names they don't follow IUPAC rules but we use them so frequently we're going to need to know how to use them regardless so don't pay attention to the main molecule I just drew a molecule to show you these different kinds of substituents this first one is an isopropyl group so it's a propyl group because it is a 3 carbon alkyl substituent and iso is regarding the shape basically if it were a straight chain propyl group we would just have 1, 2, 3 carbons extending from the main chain but this is an isopropyl group because the center carbon is connected to the main chain. and now we have a couple of butyl alkyl substituents, the sec butyl group is a four carbon substituent and it is connected by one of the middle carbons whereas the tert butyl group is connected in this fashion and the isobutyl group is connected in that fashion now the names sec and tert come from the fact that if you were to remove this from the main chain you would see that it is a secondary carbon that is attached to the main chain whereas if you remove this, this carbon here would be a tertiary carbon that is connected to the main chai tertiary meaning it is connected to three other carbons here secondary meaning it is connected to two others and then the isobutyl group looks like this. so these are some common names for a few alkyl substituents that we're going to have to know because the come up a lot. now one other interesting point about this is that sec and tert are prefixes that just like di and tri are not taken into account for alphabeticity so sec butyl is B for butyl but for some reason, and I really honestly have no idea why, the prefix iso is taken into account for of alphabeticity so isopropyl is I for isopropyl not P for propyl so just keep that in mind for alphabeticity what iso is doing but all the other ones you do disregard the prefix for alphabeticity thanks for watching guys, subscribe to my channel for more tutorials and as always feel free to email me questions