Steric Hindrance of differences of conformers of 1,2-trans dimethylcyclohexan

[jw1985]

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Hi All,

I was reading the TBR Ochem and it notes that [1,2-diequatorial > 1,2-diaxial by 2.8kcal/mol] of 1,2-trans dimethylcyclohexane. The equilibrium is also shown to favor the diaxial.

Why is this the case? I thought that there would be more steric hindrance with the diequatorial molecule because of the H's on the adjacent axial methyl groups. I thought that the deaxial would experience less hidrance because they are trans.

I have attached an image of what I'm describing.

Thanks in advance!

 

[BestDoctorEver]

Hi All,

I was reading the TBR Ochem and it notes that [1,2-diequatorial > 1,2-diaxial by 2.8kcal/mol] of 1,2-trans dimethylcyclohexane. The equilibrium is also shown to favor the diaxial.

Why is this the case? I thought that there would be more steric hindrance with the diequatorial molecule because of the H's on the adjacent axial methyl groups. I thought that the deaxial would experience less hidrance because they are trans.

I have attached an image of what I'm describing.

Thanks in advance!

Because there are more steric interactions in the equatorial presentation that is why 1, 2 diequatorial > 1, 2 diaxial. The repulsion of the methyl groups make the diequatorial molecule less stable (higher in energy).