Multiple products from a cyclic alkane undergoing an SN1 reaction?

[CycloEicosanone]

I am asked to predict product(s) of the SN1 reaction below and label the major (most stable) product if applicable.

 

Should I be drawing more than one conformation of that product? Ex. a conformation that has the isobutyl group in the axial position, since there could be more than one 1,4-cis conformation?

 

Any help sincerely appreciated, thanks!!

[hermanntrude]

it's tradtitional to only draw one conformer of any organic compound, unless one is discussing conformations specifically. Multiple conformers doesn't mean multiple products, since usually conformers interchange frequently over time except at low temperatures or when there is steric hindrance.

 

The group you referred to is a tert-butyl group, not an isobutyl

[ecoli]

since it's an SN1 reaction, you will technically get both stereoisomers. Unless you're specifically asked for both structures on a test, you could just get away with writing "(racemic mixture)" underneath the drawing.

 

edit: The way you drew it is more stable, and will be the major product, but I think some of the other stereoisomer will still form.

[CycloEicosanone]

Hey guys, thanks for the help - it's much appreciated.

 

However, I was just thinking and theoretically, could both cis and trans isomers be formed from the reaction? By that I mean the OCH3 group could be in the axial or the equatorial position. (Therefore, the trans form would be most stable since there'd be no 1,3-diaxial interactions?)

 

Lemme know what ya think!

[ecoli]

since it's SN1, it should be able to attack from either side, but actually the equitorial (in this case the trans) conformation would be more stable. Equitorial positions are, in general, more stable than axial. This is because there will be interactions between other axial hydrogens. Equitorial is more stable because it puts the large group (the ether in this case) away from potential interactions and increases stability.

 

However, you're probably still going to get the axial position as a minor product.

[CycloEicosanone]

since it's SN1, it should be able to attack from either side, but actually the equitorial (in this case the trans) conformation would be more stable. Equitorial positions are, in general, more stable than axial. This is because there will be interactions between other axial hydrogens. Equitorial is more stable because it puts the large group (the ether in this case) away from potential interactions and increases stability.

 

However, you're probably still going to get the axial position as a minor product.

 

Great, all I needed to know is that there will be cis AND trans isomers of my product...I know a lot about stereochemistry involving cis and trans isomers, enantiomers, etc but I'm just a bit unfamiliar with the products formed from a cyclic substrate.

 

Thanks for clearing things up!

[ecoli]

the exact ratios are difficult to predict anyway, and you most likely will only be held responsible for conceptual understanding.

[CycloEicosanone]

the exact ratios are difficult to predict anyway, and you most likely will only be held responsible for conceptual understanding.

 

As it turned out, there were several questions related to this matter on my o-chem test Monday and I got them all right...thank you once again

[ecoli]

As it turned out, there were several questions related to this matter on my o-chem test Monday and I got them all right...thank you once again

your welcome... it was a popular topic when I took it as well.