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Author Topic: How many isomers does C6H12 have?  (Read 59782 times)

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SimoneMeyer

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How many isomers does C6H12 have?
« on: September 06, 2009, 01:01:37 PM »

I was asked to draw every structural diagram for all isomers of C6H12. I have nine so far, but was wondering how many there actually are in total.

Thank you!
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SimoneMeyer

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Re: How many isomers does C6H12 have?
« Reply #1 on: September 06, 2009, 06:49:20 PM »

* I have these so far:




Are they correct, or completely off? Sorry, I'm just a tad confused with this chemistry course.
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MrTeo

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Re: How many isomers does C6H12 have?
« Reply #2 on: September 06, 2009, 08:40:01 PM »

There are a lot of them, in fact it's a pretty boring exercise, but it could be also quite interesting from some aspects...
Anyway, the structures you've written so far are ok, even if they are (almost all of them)  written twice, flipping the molecule horizontally. This doesn't change the nature of the molecule or its geometry: here are your attemps matched together when they represent the same species.



The two structures written in red are the cis-trans isomers for hex-3-ane, you can find out the same isomers for both hex-1-ane and hex-2-ane, while the last two don't have this isomerism (try to understand why). There are still more structure to be found: my suggestion is to start from the double bond (writing the structure in the form of my E/Z hexanes) and add substituents, remembering not to skip any cis-trans isomerism. Moreover remember that a formula in the form CnH2n can refer to an alkene but also to a cycloalkane  ;)
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SimoneMeyer

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Re: How many isomers does C6H12 have?
« Reply #3 on: September 07, 2009, 06:45:34 AM »

My brother thinks that there are 18 isomers in total, is this correct?
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SimoneMeyer

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Re: How many isomers does C6H12 have?
« Reply #4 on: September 07, 2009, 06:49:53 AM »

I found this link:

glory.gc.maricopa.edu/~elodge/C6H12Isomers.doc

It has 16 drawings and not 18... Are they correct, because some of the drawings don't resemble the ones given in my book.

Also, I've circled triangle like shapes and was wondering what the difference was between the doted and solid ones.

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sjb

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Re: How many isomers does C6H12 have?
« Reply #5 on: September 07, 2009, 07:09:20 AM »

The ones in the link are all the saturated ones ([mono]cycloalkanes). The ones you have started to draw out are the alkene isomers. Have a look at http://courses.chem.psu.edu/chem210/tutorials/stereo-drawings/stereo-tutorial.html for instance to hopefully start explaining the "dotted and solid" lines.

So neither are wrong, and both are right. This is part of what MrTeo was pointing at.
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MrTeo

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Re: How many isomers does C6H12 have?
« Reply #6 on: September 07, 2009, 08:42:17 AM »

Anyway I don't think they want you to draw also the steroisomers, it's far too difficult... my suggestion is to start from the ones you wrote and try some others (first using the double bond, then working on cycloakanes) and forget the suggestions got from the net or from you brother (even if, if i remember well, he's right  ;)) as you'll need them to check all the structures but not to write them...

Moreover consider that exercises like this don't really want you to find out all the structures (18 or even 16 are really a lot of isomers...) but to make you practise on this kind of things, so don't worry about the real answer as I think that very few of us could draw all the isomers if asked but they'd probably forget some  ;D
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The way of the superior man may be compared to what takes place in traveling, when to go to a distance we must first traverse the space that is near, and in ascending a height, when we must begin from the lower ground. (Confucius)

SimoneMeyer

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Re: How many isomers does C6H12 have?
« Reply #7 on: September 07, 2009, 08:54:01 AM »

Unfortunately they wrote: "Chaque isomère possible."
Which means every isomer possible... Would they accept the steroisomers in my answer or do you think that they would consider them as incorrect?
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MrTeo

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Re: How many isomers does C6H12 have?
« Reply #8 on: September 07, 2009, 10:40:24 AM »

Well, I think that considering that you couldn't spot the difference between dotted and solid wedged bonds you aren't really "into" stereochemistry... at least not enough to understand these isomers...

Anyway also if you want to draw steroisomers you have to start from the other isomers: finding all of them it's already a good trial  ;)
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The way of the superior man may be compared to what takes place in traveling, when to go to a distance we must first traverse the space that is near, and in ascending a height, when we must begin from the lower ground. (Confucius)
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