Thank you very much for the pictures! But would like to just clarify, why isn't there any diaxial interaction for the first structure? Isnt it 1,3 diaxial interaction? So since CH(CH3)2 is in axial, can it have diaxial interaction with the Hydrogen at the third carbon?

I wrote :

'There are no diaxial interactions between it and the equatorial OH and CH3 groups'

The 'it' here refers to the bulky group.

This doesn't mean that the bulky group has no diaxial interactions with the axial Hs.

For the configuration on top, you have 1 bulky group having 1,3-diaxial interactions with 2 axial Hs.

For the configuration below, you have 1 OH and 1 CH3 group having 1,3-diaxial interactions with 1 axial H, as well as with each other.


OH and CH3 are both bigger substituents than a single H (hydrogen is the smallest atom in the entire Periodic table).


So the combined interactions (i.e steric) between the OH,CH3 and axial H will be bigger and outweigh the interactions between bulky group and two small Hs.

Ohh yes! Finally understand now. Thank you very much!!

Welcome!