[lira]

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  1^o 2^o, 3^o alkyl groups as appropriate.
I know how to identify does alkyl groups as 1^o 2^o, 3^o 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

[KritikalMass]

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.

[jinclean]

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) 

[lira]

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.

[orgoclear]

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.

[lira]

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 ?

[Dan]

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?

[lira]

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

[KritikalMass]

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?

[lira]

I didn't take it to consideration because I don't know what to do with it 

[KritikalMass]

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?

[lira]

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

[KritikalMass]

sorry- I forgot to post the link!


http://www.cem.msu.edu/~reusch/VirtualText/sterism2.htm

[lira]

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

[KritikalMass]

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.