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Topic: graphite ring conformation?  (Read 9366 times)

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Offline discodermolide

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Re: graphite ring conformation?
« Reply #15 on: October 13, 2013, 02:39:11 AM »
Why not look at this page?
http://en.wikipedia.org/wiki/Graphite
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Offline iScience

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Re: graphite ring conformation?
« Reply #16 on: October 13, 2013, 04:05:47 PM »
i've already been to that website. it just says "C" for chemical formula. This doesn't tell me why there is no fourth group.
and for crystal structure it said hexagonal, which i already knew. i'm sorry, is this really such a stupid question? my understanding was that graphite nothing more than sheets of graphene, sheets of poly cyclohexanes. cyclohexanes have hydrogens on them. i'm asking why there is no hydrogens for each cyclohexane unit. unless adjacent layers are contributing to the fourth bond for each carbon? looking at the crystal structure of graphite i don't see how this can be the case, but if there are no hydrogens in graphite, the fourth bond must be bonded to a carbon, which has to be from one of the adjacent layers, but how can this be the case? graphite has a hexagonal close packed configuration. and some of the carbons in a cyclohexane unit will be too far away from the other carbons on an adjacent layer to form any bonds.

http://i.imgur.com/eFsrbYG.gif

i drew a red circle around the carbon that i'm referring to; the one i'm saying that would have a hard time forming any bonds with the adjacent layer. Am i looking at this the wrong way?.. should i be looking at the space filling model?..
« Last Edit: October 13, 2013, 04:19:11 PM by iScience »

Offline Altered State

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Re: graphite ring conformation?
« Reply #17 on: October 13, 2013, 06:25:25 PM »
it just says "C" for chemical formula.

Maybe that is becouse it's just formed out of Carbon.

Please, link the source where you saw that carbon was formed of cyclohexanes...

Offline discodermolide

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Re: graphite ring conformation?
« Reply #18 on: October 13, 2013, 07:32:32 PM »
That is because it is ONLY carbon. It is an allotrope of carbon.
No hydrogen, nothing but carbon, the element carbon.
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Offline willug

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Re: graphite ring conformation?
« Reply #19 on: October 14, 2013, 04:45:41 PM »
You could try googling 'bonding in graphite'. This was the first result for me. Copied below from; 'http://www.chemguide.co.uk/atoms/structures/giantcov.html'

The bonding in graphite

Each carbon atom uses three of its electrons to form simple bonds to its three close neighbours. That leaves a fourth electron in the bonding level. These "spare" electrons in each carbon atom become delocalised over the whole of the sheet of atoms in one layer. They are no longer associated directly with any particular atom or pair of atoms, but are free to wander throughout the whole sheet.
   
If you are interested (beyond A'level):  The bonding in graphite is like a vastly extended version of the bonding in benzene. Each carbon atom undergoes sp2 hybridisation, and then the unhybridised p orbitals on each carbon atom overlap sideways to give a massive pi system above and below the plane of the sheet of atoms.

The important thing is that the delocalised electrons are free to move anywhere within the sheet - each electron is no longer fixed to a particular carbon atom. There is, however, no direct contact between the delocalised electrons in one sheet and those in the neighbouring sheets.

The atoms within a sheet are held together by strong covalent bonds - stronger, in fact, than in diamond because of the additional bonding caused by the delocalised electrons. So what holds the sheets together?

In graphite you have the ultimate example of van der Waals dispersion forces. As the delocalised electrons move around in the sheet, very large temporary dipoles can be set up which will induce opposite dipoles in the sheets above and below - and so on throughout the whole graphite crystal.



Offline Enthalpy

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Re: graphite ring conformation?
« Reply #20 on: October 14, 2013, 08:57:38 PM »
[...] I heard that natural graphite is a mess; that it's not really clean layers and there are kinks and bumps all over the graphite structure.

Graphite is absent from Nature. It's strictly man-made by pyrolysis of varied compounds like tar, sisal, polyacrylonitrile, gaseous hydrocarbons.

Especially coal is a hydrocarbon, with some more elements. It's carbon-rich, but a hydrocarbon - this allows to light it, while graphite doesn't burn.

Docs about graphite differ an awful lot from an other (except when copied as usual), even for properties as basic as density. The start compound defines much the produced graphite, the process also: impregnation steps, atmosphere, pyrolysis duration. Carbon is known precisely only as diamond.

I have never read a report about a graphite single-crystal, from which some properties like density could have been measured. Since graphite sublimates first, it takes 108 bar to melt it at 4,600K ±300K (admire the precision), so I guess nobody has crystallized it.

Most materials are usually polycrystalline, but graphite is much worse: its pure and ordered form is unknown.

Offline Borek

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Re: graphite ring conformation?
« Reply #21 on: October 15, 2013, 02:50:54 AM »
Graphite is absent from Nature. It's strictly man-made by pyrolysis of varied compounds like tar, sisal, polyacrylonitrile, gaseous hydrocarbons.

Not true, http://lmgtfy.com/?q=graphite+mine
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Offline magician4

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Re: graphite ring conformation?
« Reply #22 on: October 15, 2013, 10:30:25 AM »
in addition:

Anthracite coal is up to 98% pure , naturally occurring carbon, mostly graphite

regards

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Offline Enthalpy

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Re: graphite ring conformation?
« Reply #23 on: October 16, 2013, 03:28:27 PM »
Benzene also is 92% pure carbon like anthracite is - but I wouldn't call it graphite.

As it look, mining companies also call "graphite" a coal that contains more carbon than anthracite, but it's far from what users expect from technological graphite. A matter of wording then.

Offline magician4

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Re: graphite ring conformation?
« Reply #24 on: October 16, 2013, 04:53:12 PM »
Quote
(...)but it's far from what users expect from technological graphite
no Sir: this is "technological" graphite, with all the bells and whistles  (> 94% C , if memory serves)

somewhat more than half of the world's demand in technical grade graphite of approx 1,12 million t/a  is being mined this way


regards

Ingo
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Offline WW

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Re: graphite ring conformation?
« Reply #25 on: October 18, 2013, 08:26:32 AM »
Each carbon shares three of it's free electrons with another carbon, leaving one free electron to be delocalized about the structure.  So yes graphene is an example where carbon doesn't form four bonds.  because of the free electron it can conduct electricity, one of the few nonmetallic substances to be able to do so

Offline Enthalpy

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Re: graphite ring conformation?
« Reply #26 on: October 18, 2013, 08:28:28 AM »
Technological graphite is manufactured in a long process. It's not a natural product. At 94% carbon, you have naphthalene for instance, which doesn't qualify as graphite.

You may have a look for instance at:
Survey and future trends of graphite technology, by E.J.Dunn, in 1962, ASD-TR4I1-35
www.dtic.mil/dtic/tr/fulltext/u2/274027.pdf

"There  are presently  three  practical  approaches  to  the manufacture  of graphites:  the
conventional method,  the  hot  working method,  and  the  pyrolytic method.  The  hot  working
and pyrolytic  methods  have  been  developed  to  the  point  of practicality  since  1958.

Conventional Method

The  conventional  production method  wherein  a  filler  such  as petroleum  coke  is
mixed with  a  binder,  coal  tar pitch,  baked  and  then graphitized  upward of  4500°F..."

I feel reasonable that refractory material used to make ovens differ from a fuel.

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