Achiever Ochem Question

[DAT-Scared]

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Hey Guys,
I have come across this question on DAT Achiever.
Stable conformations for disubstituted cyclohexane are exhibited in
I. cis-1,4-dimethycyclohexane
II. trans-1,4-dimethycyclohexane
III. cis-1,3-dimethycyclohexane
IV. trans-1,3-dimethycyclohexane

for some reason, I do think the explanation is enough. I thoght 1,3 diaxial will occur but the answer is II and IV.

Any help will be appreciated.

 

[Notoriousjae]

Hey Guys,
I have come across this question on DAT Achiever.
Stable conformations for disubstituted cyclohexane are exhibited in
I. cis-1,4-dimethycyclohexane
II. trans-1,4-dimethycyclohexane
III. cis-1,3-dimethycyclohexane
IV. trans-1,3-dimethycyclohexane

for some reason, I do think the explanation is enough. I thoght 1,3 diaxial will occur but the answer is II and IV.

Any help will be appreciated.

stable conformations are exhibited in the trans form because when they are on the opposite sides of the plane of the molecule there is lesser steric strain and more stability.

 

[messenger]

i took this exam yesterday and the answer, it says, is
II. trans-1,4-dimethycyclohexane
III. cis-1,3-dimethycyclohexane

can anyone explain this in more depth? 🙂
messenger.

 

[mlle]

i took this exam yesterday and the answer, it says, is
II. trans-1,4-dimethycyclohexane
III. cis-1,3-dimethycyclohexane

can anyone explain this in more depth? 🙂
messenger.

That's correct.

if you look at the chair conformation and imagine sticking in the appropriate methyl groups you should see that for greatest stability the methyls should be oriented equatorially as per the description of the answers. do you see it?

 

[Clover]

1) draw out the cyclohexanes in chair conformation

II. trans-1,4-dimethycyclohexane
III. cis-1,3-dimethycyclohexane

For these, in one conformation, they are both axial and in another they are both equitorial (less strain - more stable)



I. cis-1,4-dimethycyclohexane
IV. trans-1,3-dimethycyclohexane

For these, in both conformation, either one is axial and the other equitorial or vice versa. They can't both be equitorial so will not be as stable as choice II and III.

 

[DonExodus]

The 1-4 trans I completely see- both are equitorial, opposite ends of ring- cant get more stable.

The 1-3 cis also has them both equitorial, but it STILL wont be as stable as 1-4 trans because of the proximity.

To me, proximity (1-3 vs 1-4) would be more important than axial vs equitorial: provided they arent both axial. Thoughts?
IMO, the question should ask for the most stable. Asking whats stable is too relative....

 

[mlle]

The 1-4 trans I completely see- both are equitorial, opposite ends of ring- cant get more stable.

The 1-3 cis also has them both equitorial, but it STILL wont be as stable as 1-4 trans because of the proximity.

To me, proximity (1-3 vs 1-4) would be more important than axial vs equitorial: provided they arent both axial. Thoughts?
IMO, the question should ask for the most stable. Asking whats stable is too relative....

being equatorial is much more important than being 3 c's apart versus 2.