Aromatic Ring Polymers

[Captain Kremmen]

Are there any?
If not why not?
They would have some interesting properties I think.


This is a Phtylate, which starts off well, but then gives up on the job.
The chemical smells as satisfying as its appearance.
It is what gives cars their new car smell.
Beautiful, isn't it.

http://www.xushengchem.cn/images/image009.gif

[Forceman]

If there is a benzene ring in the middle of the resonance formula, why does it not produce a revolting odor?

[Roman]

There are structures of linked rings. Naphthalene, Anthracene, Phenanthrene, Pyrene, Benzo[a]pyrene, and Coronene, to name a few. Benzo[a]pyrene is a major carcinogen in cigarette smoke. It gets converted into a diol epoxide, which binds to DNA's amino groups, causing mutations.


If there is a benzene ring in the middle of the resonance formula, why does it not produce a revolting odor?

Because the side groups are what gives things odor. You'll find benzene rings in all sorts of aromatic compounds. Thyme and vanilla, for instance, both have phenols (benzene with an -OH) in them. Curry also contains two phenols, and has been shown to have anti-cancer properties due to angiogenesis inhibition.

[Captain Kremmen]

That's not quite what I meant.
I meant polymers, where the chain goes on for hundreds, perhaps thousands of units.
I've found this natural one, lignin in wood.
Are there any man made ones?
http://sci.waikato.ac.nz/farm/images/lignin%20structure%20RF.jpg

[leopold]

You'll find benzene rings in all sorts of aromatic compounds.
if i'm not mistaken "aromatic" is the standard name for any compound that contains a benzine ring.

[Roman]

Ohhh, polymers.
Right.

Chitin is scleretized with quinones. I can't find any images of it though. I'm unsure if it's what you're thinking of, where the aromatic rings are attached to each other. I think the quinones are added as side groups.

Here's polyether ether ketone (http://www.scielo.br/img/revistas/jbchs/v19n1/a16fig01.gif). According to encylopedia britannica (http://www.britannica.com/EBchecked/topic/468503/polyetheretherketone), they're pretty bomber.

Makes sense, as most of the bonds aren't very reactive.

Wikipedia also has an article on them. Looks like they're relatively simple to put together.

[Roman]

if i'm not mistaken "aromatic" is the standard name for any compound that contains a benzine ring.

Yup.
I was being a little tongue in cheek, since aromatic comes from a certain physical property that compounds that demonstrate aromaticity share.

[Captain Kremmen]

Yes, you've got what I mean now.
Poly ether ether ketone (PEEK) would be one.
This is a molecular diagram I found for PEK.
http://pslc.ws/macrogcss/images/tg07.gif

There's another one in the family too.
SPEEK, sulphonated........

They make very strong plastics, and are heat resistant.

[Roman]

So how do plastics work? Is it simply one VERY long string of molecules, or is that stuff held together with dipole moments?

[Captain Kremmen]

Dipolar molecules do form chains.
Water does.

[Roman]

Dipolar molecules do form chains.
Water does.

1. Water isn't structurally strong.
2. Water hydrogen bonds, which is the strongest of intermolecular forces.

PEEK is very sturdy, and doesn't look like it can form any hydrogen bonds. I am wondering what intermolecular forces hold it together.

[Captain Kremmen]

Polystyrene has rings, but they do not form part of the chain.
It must be difficult to get rings to string together.
PEEK was only made in 1962.

http://www.physics.nyu.edu/pine/research/nanocopoly/polystyrene.jpg

Thanks for your efforts in keeping this thread alive, Roman, but keeping a thread going on this section is like threading a needle wearing boxing gloves.

[Trippy]

if i'm not mistaken "aromatic" is the standard name for any compound that contains a benzine ring.


Yup.
I was being a little tongue in cheek, since aromatic comes from a certain physical property that compounds that demonstrate aromaticity share.

That was the origin of the term, the most odiferous substances in nature tend to be terpenes.

The term Aromatic in its current usage in chemistry actually refers to having a set of conjugated double bonds that are capable of undergoing resonance.

Specifically, we have Hückel's Rule, which essentially states that in order for a molecule to be aromatic, it must be planar, and it must have 4n+2 π electrons.

For example:

[14]Annulene:
http://upload.wikimedia.org/wikipedia/commons/thumb/c/c2/14Annulene.svg/200px-14Annulene.svg.png

and [18]Annulene:
http://upload.wikimedia.org/wikipedia/commons/thumb/3/33/(18)Annulene.svg/166px-(18)Annulene.svg.png

Are Aromatic, however...

[Trippy]

[16]Annulene:
http://hackberry.chem.trinity.edu/blog/wp-content/karney-cmpd1b.gif

[10]Annulene:
http://chemistry.boisestate.edu/people/richardbanks/organic/nomenclature/aromatic16.gif

And Cyclooctatetraene (or [8]Annulene):
http://www.geocities.com/athens/thebes/5118/obc/arom_fig/c8.gif

Are not aromatic.

The interesting thing about Hückel's Rule is that it brings into play some interesting aromatic compounds.

So for example, while Cyclopentadiene is not aromatic, the cyclopentadienyl anion is.

Cycloheptatriene is not aromatic, but the cyclopentatrienyl cation (tropylium ion) is aromatic, as is the cyclopropenyl cation.

There's also a class of compounds that are classed as being Anti aromatic.

Aromatic hydrocarbons have a lower total energy then their straight chain counterparts.

Antiaromatic hydrocarbons have a higher total energy then their straight chain counterparts.

[Trippy]

Then there's compounds that are classed as non-benzenoid aromatics, such as Azulene:

http://medplant.nmsu.edu/Diseases/strep/strep_azulene.gif

Which, unlike most of the Annulenes, doesn't have anything that resembles the benzene structure, or benzene structural components.

I should also point out that Hückel's Rule is only applicable to monocyclic structures. For example, Pyrene is aromatic, even though it has a non-Hückel number of electrons (14).

However, if you pay attention to the peripheral structure, it resembles [14]Annulene, and 14 is a Hückel number. Based on this you can predict that the periphery of Pyrene might be aromatic by itself, and this has been confirmed by experiments involving trans-15,16-Dimethyldihydropyrene (Pyrene with two methyl groups added trans across the central double bond) which still behaves in an aromatic fashion.

I hope that this is at least somewhat useful.

[Roman]

If you bridge [10]Annulene at the 1,6 positions with a methyl, it becomes aromatic. This is because it becomes planar, with the cloud of pi electrons above and below.

I just has a test on aromatic compounds :D

[Idle Mind]

If there is a benzene ring in the middle of the resonance formula, why does it not produce a revolting odor?
Unless they messed up the image, that would be a cyclohexane in the middle there.

[Captain Kremmen]

http://www.xushengchem.cn/images/image009.gif
Looking again at that phtylate, why wouldn't it form polymers?
Surely, in place of one of those OH groups it could bond to another phtylate molecule.

[Idle Mind]

Yes, but you would end up with a messy polymer, since you likely wouldn't have control over which phosphate bound to which.

[Captain Kremmen]

Messy polymers. I get your meaning.
Ones that bond all over the place.

Do they exist, and are they used for anything?

[Captain Kremmen]

http://www.xushengchem.cn/images/image009.gif


Looks a bit like Matisse's dancers
http://tbn2.google.com/images?q=tbn:WVOaprBjo1fRwM:http://www.hotsalsa.co.uk/danceMat.jpg

[Idle Mind]

Messy polymers. I get your meaning.
Ones that bond all over the place.

Do they exist, and are they used for anything?
Ha, that's not an official term, I just used the adjective "messy". I'm sure there are some that exist, but I can't think of any applications off the top of my head.