Most stable chair conformation question

[exquisitemelody]

A carbon-deuterium bond is shorter than a carbon-hydrogen bond. Using this idea, how many deuterium atoms assume axial orientation in the most stable chair conformation for the following molecule? (picture of cyclohexane with 3 cis H's on neighboring carbons).

The answer is 2 and the solution says that having D in the axial position is more stable. Why would the axial position be more stable? I'm going to guess it has something to do about the bond length, but I don't really get the connection...

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[BilalL]

A carbon-deuterium bond is shorter than a carbon-hydrogen bond. Using this idea, how many deuterium atoms assume axial orientation in the most stable chair conformation for the following molecule? (picture of cyclohexane with 3 cis H's on neighboring carbons).

The answer is 2 and the solution says that having D in the axial position is more stable. Why would the axial position be more stable? I'm going to guess it has something to do about the bond length, but I don't really get the connection...

Because the deuterium- carbon bonds are shorter than C-H bonds they constitute less steric hindrance than hydrogens. So you want to place as many hydrogens in the more stable equatorial positions and thus less deuteriums in the equatorial position or more in the axial position.

This question poses Hydrogens as "bulkier" than Deuterium which is not what you are used to.

 

[exquisitemelody]

Because the deuterium- carbon bonds are shorter than C-H bonds they constitute less steric hindrance than hydrogens. So you want to place as many hydrogens in the more stable equatorial positions and thus less deuteriums in the equatorial position or more in the axial position.

This question poses Hydrogens as "bulkier" than Deuterium which is not what you are used to.

Ohhh got it. Thanks

 

[MD Odyssey]

Remember that the it's largely the repulsion of electron clouds that is responsible for the energy differences between axial and equatorial configurations.