Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: lira on October 17, 2009, 03:39:38 PM
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I have who question on the subject of alkanes and alkenes which I can't figure out.
I have to give the structures and IUPAC names and common names of all C4H9- alkyl groups and identify them as 1o 2o, 3o alkyl groups as appropriate.
I know how to identify does alkyl groups as 1o 2o, 3o but I don't know what structures do I supposed to write
Second thing is : Draw possible structures of chair conformation of all possible isomers for dimetylocyclohexane. Indicate which isomer is the less stable, and identify the reason for its decreased stability.
I found only one structure
And the last thing for now is I have write the organic product of the reaction of styrene with HCl and peroxide as a catalyst
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For the first one just start drawing things like butyl, isobutyl etc. and keep going until you've exhausted all possibilities.
For the second one there are alot more than one isomer for dimethylcyclohexane. I found a bunch of them on one page by Googling "dimethylcyclohexane isomers". If you find a few more let me know and I'll come back and help explain why some isomers are more stable than others.
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dimethylcyclohexane There are many conformationabout it,first,you can find some different position on the ring of the cyclohexane to put the methly on .there are some isomer in the picture .Except the first isomer,each isomer have two conformations (I think it might be 7 isomer in all)
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Thank you for the replies.
So I found all of those seven isomers and for each two chair conformation but I couldn't find which is the less stable and why.
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first of all draw the chair conformers as these are the most stable form cyclohexane conformers. Now, the molecule will be more stable if the methyl (here) groups are in the equatorial positions.
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trans-1,2-dimethylcyclohexane and cis-1,3-dimethylcyclohexane both have conformers withe methyl groups in the equatorial positions but cis isomers are more stable then trans isomers so the most stable would be the cis-1,3-dimethylcyclohexane. The rest of the isomers have one methyl group in axial position and one in equatorial and trans-1,3-dimethylcyclohexane is a trans isomer so it is the less stable one.
Do I understand it correctly ?
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trans-1,2-dimethylcyclohexane and cis-1,3-dimethylcyclohexane both have conformers withe methyl groups in the equatorial positions
trans-1,4-dimethylcyclohexane has a conformation with only equatorial methyl groups too...
but cis isomers are more stable then trans isomers
Why?
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I overlooked trans-1,4-dimethylcyclohexane
but cis isomers are more stable then trans isomers
Why?
I found that: 1,3-series is the only cas where the cis-isomer is more stable than the trans-isomer. I misunderstand what I read but still I do not know how to find which is the less stable
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I misunderstand what I read but still I do not know how to find which is the less stable
Have you taken steric effects into consideration?
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I didn't take it to consideration because I don't know what to do with it ???
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I didn't take it to consideration because I don't know what to do with it ???
Steric effects are when the electron clouds of substituents interact with each other or other atoms such as hydrogen. Since the electron clouds are negatively charged it will cause the substituents to be repulsed away from each other. Any way, steric effects are not "good" for a molecule. So if a methyl group is axial it will be interacting with the hydrogens on the ring. Therefore, the most stable conformations will have the methyl groups in an equatorial position as this conformation minimizes steric effects.
So, looking at all the conformations of dimethylcyclohexane on that website, which ones minimize steric effects? Which ones have the methyl groups in equatorial positions?
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trans-1,2-dimethylcyclohexane, cis-1,3-dimethylcyclohexane and trans-1,4-dimethylcyclohexane have the methyl groups in equatorial position and I do understand that they are most stable and now from the rest I shoud find the less stable but I don't know how to do that
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sorry- I forgot to post the link!
http://www.cem.msu.edu/~reusch/VirtualText/sterism2.htm
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Thanks, I found what I needed
Another thing: I have to identify the more stable stereoisomer in each of the pairs
1. cis- or trans-1-isopropyl-2-methylcyclohexane
2. cis- or trans-1-isopropyl-3-methylcyclohexane
3. cis- or trans-1-isopropyl-4-methylcyclohexane
I read that in most cases trans isomers are more stable than cis isomers, so in this three cases also ?
And i don;t know which isomers are which on this picture below
(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fimg21.imageshack.us%2Fimg21%2F9606%2Fdsc0408300x119.jpg&hash=cbf6f00b3185ca5dec0d9f3d273ff649f09a83fa) (http://img21.imageshack.us/i/dsc0408300x119.jpg/)
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And i don;t know which isomers are which on this picture below
It would be alot easier for you to answer the question if you found a pic of 1-isopropyl-4-methylcyclohexane. The pic you posted is of 1,2,4-trimethylcyclohexane.
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Sorry I wrote it wrong (english is not my first language) I ment that on this picture are four more diffrent isomers that I have to identify and then say which are more stable and I know that on this picture are isomers of 1,2,4-trimethylcyclohexane but I don't know which are cis and which are trans
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Do you know what the dashes and the wedges indicate? The dashes indicate that something, in this case a methyl group, is going into the plane. A wedge indicates that something is coming out of the plane. If you have a model set I suggest you make a model- it will become immediately clear which ones are trans and which ones are cis because in cis all the methyl groups will be on one side (the drawing will either have all dashes or all wedges) and in trans at least one of them will be on the other side (so you will have wedges mixed with dashes).
But yeah- if you don't have a model set get one! A model set makes problems like this easy ;)
Good luck!
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I didn't know that. Thanks I will try to do that like you said.