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