final 2007 6b

[004253593]

Question 6B on the Winter 2007 Final Exam states:

"Draw a structure which clearly shows the most stable conformation for 1-ethyl-1-isopropylcyclohexane."


i know its a chair but how do you know which to put in axial in which to put in equatorial.

also is the molecular formula for isopropyl CH(CH3)2
what is the iupac name for isopropyl??

[ch1995]

The substituents with the larger atoms/longer chain will usually be on the equatorial plane.
isopropyl is CH(CH3)2, or 1-methyl-ethyl in iUPAC naming

[004253593]

do molecules with more carbons in a ring have more or less ring strain than molecules with less carbons in a ring?

cause on 4c on test2011 it stays that the ring strain of the cyclooctane has higher ring strain than cyclohexane-

[ch1995]

What page is the question on? (I can't find a 4C on 2011) But I think if there are too little or too many carbons in a ring structure, both will be unstable/have high strain. (5 to 6 carbons in a ring structure is most ideal I think)

[irisc23]

5 and 6 members rings are most stable because they are closest to the optimum of 109.5 in their planar structures (108 and 120, respectively). This results in the least bond angle strain. Cyclooctane in its planar form would have a bond angle of 165, very unstable. You could argue that you can stagger them by making the molecule nonplanar, however, that would result in a crowding of carbon atoms and a lot of electron electron repulsion. Therefore the most stable cyclic molecules are cyclopentane and cyclohexane.

[Chem_Mod]

In response to the first question about which is the most stable confirmation...

Always make the bigger functional group equatorial. Thus, the isopropyl group would be equatorial, and the ethyl group would be axial.

[Francesca Genera 3F]

thanks!