Nomenclature of Polycyclic Compounds: Naphthalene, Biphenyl, Anthracene, Spiro, Bicyclo

Sharing buttons:

hey guys I wanted to go over some more nomenclature stuff with you specifically

dealing with some of these polycyclic structures that you might see since we

actually never really talked about how to name those and instead of drawing

them on the board I wanted to use chem doodle because there are some

interesting features that allow you to sort of explore the nomenclature rules

as you go. I'll show you what I mean first let's just do a quick review just

to kind of get on the same page and do this simple alkane so just to remember

how we name these guys we've got to find the longest carbon chain so that is

going to be 1 2 3 4 5 6 we've got to have 6 carbons right, that's gonna be a

hexane so we can't look at this and go alright we got 5 and then an isopropyl

that's actually not gonna work so we do want to make sure we have this longest

chain and then we have to number from starting from the side that will give

the substituents occurring soonest so we want to start here this has got to be

number 1 2 3 4 5 6 and then we've got methyls on 2 & 3 so just to make sure

that we're right let's go ahead and add that name ok so we've got 2 3 dimethyl

hexane like we said so here's 1 and then 2 as a methyl 3 has a methyl 4 5 6

that's correct just to show you a feature here this is

fun you can you can alter it as you go so how many carbons do we have to attach

here to make this side to side this is this left to right chain the longest

chain well okay so what have we done here now it's still it's still this

right it's still 1 to ethyl sorry on the methyl

3 we have an ethyl 4 5 6 so that's still keeping the same parent chain the way it

before if we add one more finally we've got this this is now the parent chain

and this has become an isopropyl group instead of part of the main chain so

that is that's that one that was just a quick warmup

because now I want to get to the polycyclic stuff we've already done that

kind of stuff so let's go over some new things that we have not discussed the

nomenclature for so let's take this let's put this over here and this is

called naphthalene okay so when you have two benzene rings like this they're

fused at these two carbons this is now called naphthalene so what happens when

we start attaching things here well okay so let's put a methyl over here so one

methyl naphthalene okay so but let's look at something this is this is why

this is a cool feature we can we can see what happens if we do different stuff

instead of having to draw a bunch of structures for you we can do this very

quickly so we see that this is also one methyl what if I put it over here this

is also one methyl again and lastly this is also one methyl and so what what do

we what does that tell us well these are all identical positions at first because

we can rotate that molecule right we can rotate it any way we want we're gonna

get the same thing so that's why all those positions are identical but let's

say we put the one there where can we go all right well what is this so we've got

one two so clearly we're gonna be numbering in this way this looks like

position 3 this will be position 4 now what about this this cannot

accommodate a bond so we're actually not gonna count these two carbons in the

numbering scheme so this will be position 5 this would be 1 5 dimethyl

this would be 1 6 dimethyl this would be 1 7 dimethyl and then lastly this would

be 1 8 dimethyl now what if we start with something else let's put it over

here now we've got 2 methyl so that's counting this as carbon 1 so this has

changed what we count as carbon 1 so let's take that and then let's add

another one let's go over here but now look at what happens we

do not keep this as carbon one as carbon two and this is carbon one remember that

we're going to number it so as to give the lowest set of locants to the

substituents so before this was carbon one and this was carbon two and we had

two methyl naphthalene but if we put it over here it's automatically going to

count this carbon is carbon one remember that any of these four could have been

carbon one and if it does this now we've got one two three four five six one six

is lower than if we went to three four five so that's gonna be a better

numbering system for that and we can just draw a methyls everywhere and and

see what ends up happening we can just look at the name so clearly this is one

two three four five six seven tetra methyl instead of one two three four

five six so we always want the lowest set of numbers and specifically starting

with the lowest number that you can so that's naphthalene let's move on to

another type of molecule let's do a by phenyl so let's take this let's get the

name so there's our by phenyl so this is different than naphthalene

right because they're not fused at two carbons worth we're just connected by

this single sigma bond here between these two rings so that's by phenyl now

let's start adding substituents so what what if we do this so now it says ortho

phenyl toluene so by adding this substituent we're changing the naming

scheme because we're counting this whole part as toluene right because toluene is

a benzene ring with a methyl group on it and there's a phenyl substituent alright

this is a phenyl substituent and they are specifically they have an ortho

relationship to one another because they're one apart we have a methyl right

here and we have a phenyl right here they're one away so that's an ortho

relationship so--that's ortho phenyl toluene now let's add another one and

see what happens so now we have three phenyl ortho xylene

so it seems that what's happening is that we're changing the parent name on

the basis of the substituted phenyl and what that becomes because the thing is

that a benzene ring with two methyls on it is called a xylene right so let's

just for reference let's show this name so that's toluene and we can see that

that's ortho xylene that's meta xylene and that's para xylene so clearly xylene

is the name for a phenyl ring with a benzene ring with two methyl groups on

it and then we have ortho meta or para to describe their spatial relationship

so over here we're taking this to be the main part of the molecule we're saying

that this is an ortho xylene and then on ortho xylene right if these are the two

right carbons with the methyls there if we go one two three remember lowest

numbering scheme possible so this would be one two three on carbon three we have

a phenyl group so that's three phenyl ortho xylene and we could have all kinds

of fun with this we could we could then come over here and start adding carbons

over here and see what happens so now three meta tolyl so this is now not

three phenyl but we're saying that it's a tolyl because it's a tall toluene

substituent and it's on carbon 3 so this 3 refers to carbon 1 2 3 and then this

meta refers to this meta relationship this methyl is meta to this whole group

over here so starts to get pretty complicated but

what's cool about this is you can just start putting carbon stuff anywhere you

want and see what happens to the name and as you look at what changes with the

name you sort of the nomenclature rules so okay so that's

a biphenyl let's look at something else now let's look at we did naphthalene so

let's do that was two rings put together now let's put three phenyl rings in this

way and let's get that name and that's called anther scene so naphthalene two

rings three root three rings we've got an through scene and so how is this

numbering scheme gonna go let's try let's try one there okay so that's one

methyl anther scene if we put that there again one methyl there's one methyl

there's one methyl okay so clearly we've got four options here for where number

one it's going to go and that makes sense because if we take that molecule

and we rotate it 180 degrees like that in the plane it would end up over here

so they'd better be the same spot that makes perfect sense so let's do number

one okay so which which way were you going to go let's see what this position

is so that's clearly two so we have one and two because if we have one to

dimethyl that's what it would be over there we've got three over there we've

got four okay so clearly we're going around the ring in this way so should

this be five let's see if this is five no it's not that's ten so what what is

five instead if we go over here okay so if we continue in clockwise fashion to

the other edge most ring outermost ring now we've got five now we've got six

over there now we've got seven over there and we've got eight over there and

then we go to these central carbons if we continue in clockwise fashion we've

got nine right there and we've got 10 right there so we have just sort of

discovered the numbering scheme for anther scene we know that we're gonna

define carbon one and then we're going to go a

that ring whoops we're gonna go around that outermost ring and then we're gonna

skip over to the other outermost ring and finish that off before we do the

middle too so we can we can throw some methyls on there so this if we put that

there we're defining this to be carbon one because that would make this too and

that's the lowest that can be and then let's put that over here so that'd be

2 10 so that's how we're gonna number that and we can just arbitrarily put a

few on here and see what we get 2 7 9 and we can just do examples all day

and see what happens to the to the name there okay so we've done some aromatic

ones let's try some aliphatic ones let's try this let's try we're gonna take a

three membered ring here and now let's attach a ring there actually before I do

that let's name it

okay now let's attach a ring right here so what is the what is this scheme here

clearly we're going to call with we're gonna use this word spiro here and so we

what what it is is we've got a cyclopropane but we can't we can't name

this a cyclopropane substituent it's not a cyclopropane substituent we would need

a sigma bond between them so that's not that that's not the way we can go with

this instead we have to recognize that this is a this is a we're gonna call it

a pentane because it has five carbons so one two three four five but it's a Spiro

compound and what these numbers mean is we're naming the number of carbons

present in each ring apart from the one that joins them so here's two and here's

two and there's five total so we say it's spiro, spiro refers to this

orientation and then there's two carbons here two carbons there and there's five

total so it's a pentane so what if we add a four membered or a five membered

ring right there so again Spiro we're gonna see Spiro with all of these and

then now that we have two different sized rings we're gonna name we're gonna

we're gonna refer to the smaller one first

so here are two carbons that's the two right there and then here's one two

three four so there's four carbons there and so four plus two plus the one that

joins them remember there's always going to be one more because we're not

considering this one that connects the two rings in this scheme so add one to

get seven that's a heptane likewise let's put six so again it's pretty easy

to see it's pretty easy to know what to do we've got a three membered ring we

don't count that one so we've got two we've got a six membered ring we don't

count that one so we've got five but then altogether the five plus the two

plus the one that joins them that's eight so this is Spiro two five octane if

we want to start adding substituents let's say like that this is how we're

gonna number it we've got two everything is the same but if we've

added a methyl group let's get rid of that we're going to we're going to

number from the smaller ring so we've got two carbons here this would be

number three and then four so that's how we're gonna number we're not going to

start numbering on the larger ring we're gonna start numbering from the smaller

ring okay let's do one more type of one more type of compound here let's take a

let's do a seven membered ring and then let's get the name so we have it so

we've got cyclohexane and now let's make a bridgehead carbon okay so we've made a

bicyclo structure so the other one was Spiro now we're looking at bicyclo and

the way that we're going to name these is first we say it's bicyclo and then

we're gonna we're gonna just it's kind of like the Spiro we're gonna we're

gonna give the numbers of carbons associated with each ring and so we're

gonna go from biggest to smallest so over here we have one two three so

that's your three one two three and then over here we have two and so that's the

two and then right there we've got one so there's your one and total there are

eight carbons remember we had cyclo heptane and then we added one more so

that's eight that's octane so this is bicyclo three two one octane now let's do

something kind of cool because this looks confusing what if we clean it up

and do that okay so that gives you a little bit of a better sense of what

this molecule actually looks like we can see how you can there's a five membered

ring over here this is a six membered ring this is a seven right if you can

just kind of see the different rings in this pseudo three-dimensional way

let's do nine why not okay and then

let's do let's go like that so what do you think this is gonna be it's gonna be

by cyclo and then how are we going to number this remember we've got the most

first so one two three four we need the four and then we've got three and then

we've got two so we need four three two and then we refer to the total number so

that's an indicator so because we started with nine we added

two more for total 11 that's an undecane and we have four three two

and one more time let's just make this look the way it should look and that's

what that looks like so that's it I just wanted to show you some fun ways to

explore nomenclature rules for these trickier polycyclic compounds obviously

we could do this all day there are many more types of molecules we could look at

but that's what I want to go over for now those are some common ones with

naphthalene anthracene and the Spiro compounds and the by cyclo compounds so

I'll see you next time