Hydrocarbons - Naming Highly Branched Alkanes (IUPAC Style) Video Lecture

[Music]
hey everyone its Casey from the Montreal
student Network and today we're gonna be
looking at the you pack names associated
with the highly branched alkanes we're
basically going to look at what happens
when we have different kinds of
substituents so say a methyl group and
an ethyl group in the same compound on
the same parent branch now remember the
main rule number one you want to look
for the longest branch so let's do this
we're gonna start the numbering while
talking and you can see right now I've
switched over to bond line four when you
get over to these longer chains it's
because it's really really
time-consuming to draw out the ch3 ch2
ch2 you know so you really want to get
used to the bond line and I'll walk you
through it in case you're still a bit
flimsy with it so first we're going to
count the longest carbon chain and it's
pretty evident from this picture I'm not
trying to trick anybody so one two three
four now it's a longer chain if we
continue in this way five six seven and
eight now we want to make sure we
associated the lowest possible number to
this substituent right over here so we
can count one two three four five if we
were to went backwards we were to had a
five over here and that would not have
been the lowest possible substituent so
that would have been the incorrect
answer so this is the correct way to
number it so we see that we have eight
carbons and that would be octane so
we're gonna remember that octane right
now and that's going to be our parent
compound actually let's write it over
here
octane octane parent now what is our
substituent that we have well using the
alkyl group naming that we looked at in
the previous video we can count one two
and there is two carbons over here two
carbons
and that is a derivative of ethane its
ethyl ethyl group so we're gonna use the
standard u-pack naming and we're gonna
call it four - Ethel so that indicates
that our ethyl group with two carbons is
on the fourth parent compound and the
parent compound is octane so for ethyl
octane is what we have right here now
that was simple that was a little start
a little warmup
now we get into the more complex stuff
down here so like we do we're gonna have
to number it to give the lowest number
to the first branch now we don't care
what the branch is we see all right over
here we have an ethyl group and right
over here we have a methyl group now
here I'll circle the carbons that are
belonging to these groups you guys can
see those are two carbons and this one
carbon for the methyl group right down
there
so we know we have e is a starting
letter for this one and we have M
starting letter for this one we're gonna
want to arrange them when we do the name
in alphabetical order now saying that we
do not want to number them in
alphabetical order we do not want to
give the lowest number to ethyl if it
doesn't actually appear first we want to
give the lowest number to the first
branch that appears when numbering from
one of the ends of the longest carbon
chain now we know the longest carbon
chain is right over here
we can either number it one two so bad 2
1 2 3 and give three right here or we
would number one two three four I'll
write them out one two three four five
would be the lowest no that's not good
that is not Laura last time I checked
five is not lower than three so we're
gonna continue numbering it in this way
three four five six seven and eight so
it's obviously another octane parent
like the previous problem we to keep it
octane parents for this video and we see
we have a methyl group on the third
carbon and an ethyl group on the fourth
carbon so how are we going to name this
now we have two two
substituents we want to arrange them in
alphabetical order it does not matter
that the 4 is associated with ethyl
which II comes before M and the 3 is
there that does not make a difference so
when we're gonna be writing out this
name we're going to just take it solely
we're gonna write 4 - Ethel now we're
gonna put another - always put hyphens
to separate the numbers from the letters
let's make it that the common rules so
you don't get mixed up with commas when
you have multiple substituents of the
same kind three methyl now what is our
parent compound and octane and once
again octane thinking of an octagon for
eight carbons so what do we see with
this radio this speaks a lot this
teaches us a lot of things this teaches
us that four is where we can find the
Ethel three is where we can find the
methyl and our parent compound has eight
carbons and arranging them in
alphabetical order is the key right out
e comes before M in the alphabet and
remember like I said last video when you
have butyl substituents if you don't
have any other beutel's only one
substituent you will just use consider
as a b but say you had sexual and
tert-butyl you would be ranking them s
for sec-butyl and T for tert-butyl so
you can compare those two but against
anything else it's considered a B it's a
little confusing but once you get into
the more advanced examples you'll see
what I'm talking about I'll talk about
those in the next video when I do a bit
of problems from the book that we've
been using so let's move down to the
last example that we have right now
whoops I forgot to add a branch right
there there we go that's the example we
want to look at right now simple we're
just gonna be making it a little bit
more confusing that's that's how we do
we slowly stack on more confusing
entities to the problems and we can see
right now that we're gonna have the
Greek die prefix going on because we
have two methyl groups so in case you're
still struggling with bond line I'll
circle the carbons that belong the to
each of the appropriate alkyl groups so
we can see a methyl group right over
here another methyl group over here and
an
the group right here spread it out
methyl methyl and ethyl and our parent
compound it's still gonna be octane
we're keeping it like that we don't want
to change anything up right now so we're
gonna number it and we're gonna number
it giving the lowest first number to the
first branch that appears and you can
see that numbering one two three
opposed to numbering 1 2 3 4 3 is a
lower number so 3 will be the lowest
start like that 6 9 and 8 now what we're
gonna want to think about here is you'll
see we're gonna put everything out
you're gonna have two methyl groups
right now and like we talked about
that would be dimethyl we're gonna put
you know gonna have the numbers before
and then we're gonna write and I mess up
now we get a little bit of a problem
we have dimethyl and then we have the
ethyl substituent up here which one
comes first you know the M comes B comes
after the e but the D comes before the e
so what rule takes you know what what
takes precedence over the other you do
not consider the Greek prefixes to
indicate how much of a certain
substituent you have when doing
alphabetical order so as far as you're
concerned this is valued at an M this is
valued at an e so to name it the e comes
before so ethyl is on the fourth carbon
so we can call this for - ethyl another
- because we're always separating
numbers from letters with hyphens now we
have two different you know methyl
groups here so we need to write both of
them and you're going to want to put
those in increasing order so put the
lowest one and then followed by the
higher one so three comma five numbers
are separated by commas - two separate
now we're gonna have dimethyl and then
our parent compound has eight carbons
octane and that is how you name these
advanced structures so we learned a lot
of things we see here that alphabetic
order is important and you do not
consider dye when doing the alphabetical
order or tri or tetra or Penta or hexa
or whatever you go up with the Greek
prefixes you do not take those into
consideration you only take the actual
substituents name so you see right there
that's how you name it and E comes
before M in the alphabet and that's you
want to do it if you have more
substituents you follow this exact same
pattern very specific rules if you
follow the protocol I'm showing you
right now you will not get confused if
you just try to tackle everything at
once you know it does become a lot of
information to look at so we saw how to
you know we're starting to get more into
bond line right now it's important that
you start adapting to it because if
you're going to write this all out ch3
ch2 ch2 it's going to take a lot of time
so we have any questions any comments
you can either reach me on Twitter or
you can leave a comment on this video
and I will get back to you as soon as I
possibly can thank you very much for
watching and have yourselves a great day