Let's talk about IUPAC nomenclature of substituted benzenes, so we are going to follow the same
road map that we always have but there will be a few differences. First circle the parent
chain, label the groups, number that parent chain and number four we are going to put
the name together and we are going to remember stereochemistry at the end. So with monosubstituted
benzenes, one substituent, there's a few compounds we just have to learn the name of, they are
going to be our priority groups for benzene nomenclature, they are going to act like a
"parent chain". So first aniline here we have NH2, anisole is an ether, benzenesulfonic
acid, benzaldehyde, benzonitrile, benzoic acid, phenol, and styrene, also toluene is
one that we are going to learn for the monosubstituted benzenes. Going to be named as parents we'll
see more on that coming up. Ok other substitutions such as chlorobenzene just take the simple
name of the group and add benzene at the end. and nitrobenzene, ok so we might have bromobenzene
and so forth. If there are alkyl groups on the monosubstituted benzenes, if they are
nonambiguous groups, you can still name as a benzene, so isobutylbenzene, four carbons,
isobutyl there's no ambiguity about what "butyl" we are talking about it's isobutyl so we call
it isobutylbenzene and there should be no space there and ethylbenzene is also non ambigous
because we can attach to either position of an ethyl group and it is the one position
no matter which carbon we attach to. But if the side chain is ambiguous, we have to name
the side chain as a phenyl group on the parent chain, so 1-phenylpropane looks like this,
1,2,3 carbons where the parent chain is actually propane, 2-propane is isopropane or isopropyl,
so isopropylbenzene is an acceptable name because isopropyl is unambiguous but we say
propane it could be the one or the two position so we say 1-phenylpropane, and generally anything
larger than an ethyl group is going to need this system of nomenclature. So we could also
have 2-phenylpentane, so the parent chain is 1,2,3,4,5 and we connect at the two position
of pentane so that's a 2-phenylpentane, that phenyl group there. For disubstituted benzenes
we have substitution patterns of ortho meta and para, and so ortho looks like this, if
we have one group here ortho to that group would be at this position or ortho could be
at the other position here, ok, so the same positions are both symmetrical for ortho substitution
so two groups side by side on the benzene because it's planar. meta would then refer
to 1,2,3 away, theres the meta position, there's ortho, there's meta. the other meta position
would be there so either one of these two could be called meta. And then para is directly
opposite the benzene ring so the benzene substituent is in the 4 position relative to the original
group. So let's look at a couple of...well these three we have to name with common names
because they have specific names that are retained in the IUPAC system, there are many
more of these but these are the only 3 we are going to learn for this class. Especially
those with carboxylic acids, there's tons of special names that you could learn if you
wanted to. We'll stick with these 3. So there's ortho-xylene, two methyl groups so if it's
ortho-xylene we'd say o-xylene, then cresol is a methyl group and a hydroxy so it's like
a phenol but it's also got a methyl, that's called cresol, there's ortho cresol, we could
also have meta cresol and then toluidine has a methyl and an amine so we could end up having
para toluidine. Just got to learn those substitution patterns. And if this disubstittuted benzene
has a priority group, we have to circle the parent chain so circling the parent chain
includes the priority group, it does so for both of these. Name anything that intersects
the circle, then we number starting where our parent is and minimize the group, 1,2,3...4,5,6.
1,2,3,4,5,6 and then we want to put that name together. So this is 3-chlorophenol it could
also be called meta or just m-chlorophenol. And then the other that we have here is a
2-ehtylaniline or it could be called an ortho-ethylaniline. Either one works. What if this disubstituted
benzene does not have a priority group and so here we would have a para...well let's
go through our naming rules in order (never take a shortcut) so no parent here so they
are named as regular groups. there's chloro...there's nitro vs. ethyl and so we then number we have
a tie, either one can get the 1 or the 4 because they are both chloros but here ethyl gets
the 1 because it's lower alphabetically. So the same alkane nomenclature rules apply,
put the name together and we have a a para...a para dichlorobenzene or we have a 1,4-dichlorobenzene.
Either one works. Ok then for our other example we have a 1-ethyl-2-nitrobenzen or an ortho
ethylnitrobenzene. Either one is acceptable. If we have 3 or more substituents, and we
have to consider the case where we have priority groups. OK so here we have an anisole and
here we have, oh 2 priority groups, benzoic acid and phenol. In our priority chain carboxylic
acids have greater priority than aldehydes and ketones have greater priority than alcohols,
and so we end up picking the priority group here. So this would end up being a hydroxy,
this would be an ethyl and so we number, putting the 1 on the priority, then lowering the next
number 3,4,5. 1 on the priority, lower the next priority group 2,3,4,5,6. So then we
put it together and we have a 2,5...can't use ortho, meta or para here because there's
more than 2 substituents...so we have a 2,5-dichloroanisole. We also have a 6-ethyl-2-hydroxybenzoic acid.
and there is a second word here for acid. 6-ethyl-2-hydroxybenzoic acid. Then if we
are without priority groups or we have more than one of the same priority so here we have
no priority groups so the parent is benzene, but if we have more than one of the same priority
that group loses it's priority. so we can see the same thing occur with toluene as well
and if we go through and look at this..we end up when we number 1,2...1,2,3,4,5...1,2,3,4
so we can put a lower number overall of 1 next lowest would be 2 and then a 4 (as opposed
to a 1,2,5). Here we can have a 1,2,3 here we can have a 1,2,3 as well. What we end up
with we end up with alphabetically bromine comes first, 2-bromo-1,4-dichlorobenzene and then where we have more than one of the
same priority group we lose our priority because you can't pick one or the other and so you
end up with a 1 or excuse me a benzene-1,2,3-triol so it's named like a normal alkane alcohol
and then here at the end we have alkyl groups that would not be named with that split convention
(benzene-1,2,3,-triol) we have methyls instead so here we have a 1,2,3-trimethylbenzene so
remember alcohol nomenclature we could also say 1,2,3-benzenetriol as well. Ok so either
one works there but trimethyl benzene would be the other so a couple of examples to finish
out the more elusive rules that we don't normally see in the textbooks.