Let's talk about IUPAC nomenclature of alkanes.
So this video specifically addresses an introduction to IUPAC nomenclature considering alkanes
but predating IUPAC nomenclature involving priority groups and stereochemistry so we
are not quite there yet involving this video and more videos will follow that add priority
groups and stereochemistry to the equation.
So let's look at our nomenclature roadmap, these are the four general steps that we have
to do to give ourselves the most likelihood of getting to the right answer and getting
to that IUPAC name.
So the first three steps are like diagramming sentences we are going to circle the parent
chain, we are going to label the names of groups intersecting the circle then we are
going to number the chain physically on the page so that we have all the tools that we
need to put the name together using the proper formatting at the end so the first three don't
actually get us the name on paper but they get us ready to assemble that name properly
using all of the steps and tiebreakers involved.
And so the details and the tiebreakers must be followed in order so there is a rhythm
to this there is a method to it and if we go in order we will get to the right answer
if we go out of order we are going to run into trouble.
So number one we have to identify the parent chain and the longest to longest carbon chain
and if we have a carbon to carbon chain that's tied, multiple chains, then the most branched
is going to win.
Ok so we've got to do enough practice to see that and we'll look at a few examples at the
end getting the rules out here.
There are more tiebreakers than this but my course will not look at examples with more
tiebreakers than this but you can find the additional tiebreakers in the IUPAC Blue Book
and currently it's available in an online html version although that is not guaranteed
to last forever but currently it is there.
So the next thing we've got to do is name the groups and so we have our simple prefixes
based on number of carbons to which we add the suffix -yl to so methyl, ethyl, propyl
depending on how many group carbons there are.
And then we have branched groups that have common names ok so we are going to look at
these first here if we consider an infinitely long parent chain here that we have circled
intersecting this parent chain we have an isopropyl group here ok so the branching this
iso- functionality here is what designates an iso- group so i've included an isobutyl
to kind of designate that so four carbons isobutyl 1,2,3, and 4 carbons and then isopentyl
we would have 5 carbons involved again that branching at the end is what gives it the
"iso-" and the iso is always acceptable it not ambiguous at all, however, there are only
limited other prefixes that we can use and other designations "sec-butyl" for example
looks like this and there is no other sec that we can use without being ambiguous so
sec-butyl or s-butyl and the butyl is alphabetized but not the "s", iso- does get alphabetized
with the name ok so we alphabetize by iso but not by sec and not by "tert" so butyl
here and pentyl would be alphabetized so we've got sec-butyl we have tert-pentyl or tert-butyl
excuse me and then tert-pentyl as unambigous groups and then I've compared the iso group
isobutyl to sec butyl considering this infinitely long parent chain, that's how they would look
after you circle the chain.
That's how they would look, ok.
So you're getting plenty of rules here and examples teach this better but we've got to
get them down so just copy these down or pause or whatever you have to do to get them down
because we are going to read through these a little bit fast and then practice as we
go so branched groups, groups with groups.
We can name the ones that have common names as they are or we could name those as branched
groups as complex groups and the way we do that is wherever we are attached to the parent
chain so here I'm going to circle the parent chain, wherever we are attached to the parent
chain we have to assign the number 1 to that position and then we find the longest chain
either way using the parent chain rules for that group and we circle that, and then anything
intersecting that's a group of a group we give a name to, methyl there's methyl again,
and then we number that chain 1,2,3 just like we did so the 1 position is already there
but 1,2,3 on the group as well, and for this particular example we write the name of the
group we place it in parentheses, it would be a 1,2-dimethyl..three carbons is a propyl...and
it goes in parentheses in the final name.
Ok and so we'll practice putting those into a name momentarily.
Ok so number 3 in the road map, we've circled the parent chain, we've named our groups,
number 3 we number the parent chain we put the lowest number on the first group, so it
doesn't matter how long the parent chain is, it's better to put a single one on a bromine
on this side of the chain and put 1,2,3,4,5,6,7,8,9,10, 11, two 11's here in the name than it is to
put two two's and then 1,2,3,4,5,6,7,8,9,10, 11 on bromine ok so it's much better to name
it with a lower number initially than the average number, so the lowest number on the
first group possible and then we if we have a tie we move on to the next and if there
is an absolute tie it depends on the alphabetical order of the group names and we'll see that,
ok for example if we are numbering this chain, bromine wins it gets the 2 instead of fluorine
because it comes before fluorine in the alphabet.
And the last thing we have to do is assemble the name, ok, and every groups that is named
that intersects that circle has to get a number.
If we have multiple of the same groups we use this set of prefixes, di ,tri, tetra,
penta, hexa, hepta, octa, nona, deca hopefully we won't have more than that if we do there
are prefixes for it, but we'll have to look those up.
Separate numbers from numbers with comma's so if we have a 1,2-dimethyl and separate
letters from numbers with dashes ok so we've got a dash here and we've got a comma here,
and then we order the groups in alphabetical order in the name not based on the number
based on the alphabetical order and we don't number based on alphabetical order unless
we reach that tiebreaker so we have to go in order in order to get the correct name.
Parent name goes at the end with no spaces ok so lets do a couple of examples where we
put all the rules together.
Rule number one circle the parent chain so we've got to have the most branches, we've
got a couple of options here.
Ok so we've got 1,2,3,4,5,6,7 then 1,2,3,4,5,6,7 ok and then if we go 1,2,3,4,5,6,7 we have
a seven membered parent chain.
So the most branches, so we circle this parent chain because we end up with 3 branches instead
of 2.
Either of the other two would have only given us two branches and the rule says we have
to maximize the number of branches if there is a tie.
So we have methyl, we have methyl, and we have 1,2,3 carbons is propyl, so there's number
2 we write the names of the groups.
Then 3 we number the chain putting the lowest number on any group so we can put a 2 here
or a 2 here numbering from either side 3,4 or 3,4 so there's a tie looks like this is
a symmetrical chain so why not just pick one and go 1,2,3,4,5,6, and 7 ok we can number
the other way and get the same name because of symmetry there, and then finally we put
the name together following our rules we have a in alphabetical order a 2,6-dimethyl-4-propylheptane.
Ok no spaces.
For the second example we have a 5 membered ring and a 1,2,3,4,5 membered chain so the
rule is if we have a ring vs a chain the ring if it's tied in number of carbons wins.
If chain is longer, the chain wins.
If the ring is larger in number of carbons then that wins.
The one thing we cannot do is go through a ring and into a chain so THIS is illegal,
we cannot go past this point and take a ring into a chain we have to separate the ring
from the chain and pick one or the other in this case the tiebreaker 1,2,3,4,5 in a row
vs a 5 membered ring, the ring wins.
Right the names of the groups so we have a bromo, so alkyl halides end in "o", bromo,
chloro, fluoro, iodo and then methyl again, and then finally we have a 1,2,3,4,5,6 membered
iso type group so this is an isohexyl, we could also name it as a complex group and
say OR either one we could say carbon that attaches is carbon 1, circle, methyl, and
then 1,2,3,4,5 we have a 4-methylpentyl group.
Either or isohexyl or 4-methylpentyl work so lets name it two ways.
Ok so if we name it as an isohexyl, the "i"gets alphabetized, if we name it as a 4-methylpentyl
we always take the first letter unless we have a 3-methylpentyl, then we would have
to use the 3 instead of the 4, but since it's just letters at work here unless everything
is identical the number drops out and we just use the letters so we're alphabetizing here.
So let's do isohexyl first, two different names based on how you decided to name those
groups.
So let's actually number the chain first we forgot number 3, so we've got to put the lowest
number on any group and so the lowest number could be a 1,2,3,4 so a 1,2,3,4 if we start
with the methyl 1,2,3,4 so that's tied and we can get 1,3 so the isohexyl's out because
the best we can do is 1,3 so we end up putting a 1 on the bromo because it's alphabetically
before methyl if we can do a 1,2,4 with both bromo and methyl so we take the bromo since
it's alphabetically first we can lower the number that way so back to putting the name
together.
We have 1-bromo iso comes next, 4-isohexyl, 4-isohexyl, 1-bromo-4-isohexyl-2-methyl...cyclo
for the ring...parent chain is a cyclopentane so 1-bromo-4-isohexyl-2-methylcyclopentane
is put together.
Now if we named it as a 4-methylpentyl, now 1-bromo still comes first but then methyl
vs methylpentyl, methyl ends and methylpentyl is still going so the methyl is going to come
first alphabetically and then finally making sure we put this in parentheses we have a
4-(4-methylpentyl)cyclopentane all one word ok so we've...let's make sure we get this
all as one word if we can...there we go ok so 4 and again when we write this up here
we should put parentheses here alright (4-methylpentyl)cyclopentane as we diagram this out.
Last example.
Ok we've got quite a chain here and so we want to pick the longest carbon chain with
the most branches so we've got a 1,2,3,4,5,6 a 1,2,3,4,5,6, a 1,2,3,4,5 no 1,2,3,4,56,
ok so that is six as well.
1,2,3,4 branches I think we've got one, 1,2,3,4 branches looks right to me here.
As we went through those 1,2,3,4,5,6.
Ok so 4 branches wins the others seem to have only 3 branches each and so then as we write
the names of the groups fluoro, chloro, ethyl, and ethyl, and looking through at numbering
number 3 we can number a 2,3,4,5 or a 2,3,4,5 so we are tied as far as numbering goes so
we've got to resort to alphabet, so if we start with chloro vs. fluoro 1,2,3,4,5 and
6 so we lower the alphabetically first group in the name.
Now that we've got it numbered we can put this together , chloro coming first we have
a 2-chloro-3,4-dimethyl...the di- is not alphabetized, what you write up here is what gets alphabetized
not the prefixes thats why we write those before we add the prefixes so 3,4-dimethyl-5-fluorohexane