so now let's take a look at some
other kinds of substituents other than alkyl substituents
a very common one is halogens. when you have a hydrocarbon
with halogen substituents these are called haloalkanes
so here's one, and now all the rules are the same
so first we can identify the longest carbon chain
being very careful to realize that this
bromine atom is not a carbon atom, this is a bond to a bromine atom so that
does not count as a carbon
so we have a five carbon chain
we are going to number right to left because there is a substituent
on carbon one on this side
luckily the rest is the same at this point so we're going to see that we have
a methyl group
and then we have 3 halogen groups
and these are going to be abbreviated thusly
we have bromo,
chloro, fluoro
and iodo, depending on whether it is a bromine, chlorine, fluorine or iodine atom
and the rules for alphabeticity are also the same
so the substituent that occur soonest alphabetically
is bromine and we have two of them, one on carbon 1
and another on carbon 3 so we will list that first but we do have two of them
so we will list them simultaneously
it's going to be 1,3-dibromo
next we have a chlorine on carbon 2 so that is
2-chloro
and then lastly the methyl group on carbon 4
and it is a pentane
once again alphabeticity dictates that we are going to have bromine
before chlorine before methyl and
bear in mind that the prefix di is not taking into account for alphabeticity.
let's talk about another substituent, the hydroxyl group
a hydrocarbon that bears a hydroxyl group is called an alcohol
so a hydroxyl group is the OH group that we see here
now be the hydroxyl group is a group that modifies the behavior
of a molecule sufficiently that we
deem it necessary to modify the suffix of the molecule
so this is no longer going to be an alkane
it is an alcohol and so the suffix is no longer
ane, its ol, O-L. so here
we see that we have a five carbon molecule
we're going to have to number this right to left to give the hydroxyl group
occurring sooner and so now what we're gonna call this
is 2-pentanol
so we are going to have to
say where the hydroxyl group occurs
but we're going to list the presence of the hydroxyl group in the suffix
of the molecule now so this is ol for an alcohol
now here's the thing, the hydroxyl group
takes priority over alkyl and halogen
in terms of the priority of numbering left to right or right to left
so what that means is for this example we will identify the longest carbon
chain just as we normally do,
however whereas before we would
probably have decided to number left to right because an iodo group would occur
on carbon 1 if we number from the left, because the hydroxyl group takes priority
over any alkyl or halogen substituent we're gonna have to number
from the right to the left because that will specifically give
the hydroxyl group occurring soonest
so we will number this way only for the reason
that it gives the hydroxyl group occurring sooner
so now we will simply as you would expect list
what we have, we have
6-iodo-2-hexanol
so let's summarize what we learned today. if we want to name
a simple hydrocarbon there are two things we must do, the first thing we have to do
is identify the longest carbon chain. then we have to number that chain
from left to right or right to left depending on which direction gives a substituent
occurring soonest. if a substituent occurs on the same carbon regardless of
which side we start from
we will number it so as to give the
one occurring sooner alphabetically as
occurring soonest or if we have a hydroxyl group or some
other substituent that takes priority over
alkyl or halogen we are going to number it so as to give
that substituent occurring the soonest. once we have numbered
the carbon chain the second thing we must do, that is completely separate
from the algorithm that we used to assign the
carbon numbers is that we must list the substituents
alphabetically. if one particular
substituent occurs more than once we will name
all of them at the same time with a prefix indicating
the frequency with which that substituent occurs
also remember disregard almost all prefixes
in terms of alphabeticity except for iso
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