Synthesis of an epoxide from 1,2-diol

Why is there no formation of epoxide when the two OH-groups are on different planes? I do understand the epoxidation mechanism. However, I would be grateful if someone cleared the specific requirements for epoxidation.

• Read up on under what conditions SOCl2 reacts with ROH to give RCl. One set of conditions is SN2; another "internal return", i.e., no inversion. – user55119 Jun 30 at 11:41

Extending this to the current question , alkyl chloro sulfite 2 is formed.$${Cl^-}$$ attacks in a $${S_N^2}$$ mode to give 3.
Alkoxide and chloride in 4 are in correct trans configuration for a $${S_N^2}$$.This results in 5(B in your scheme).
If we take C in your question , and follow the scheme above, 9 is formed.In 9 alkoxide and chloride are not in correct configuration for $${S_N^2}$$.Therefore C in your question does not undergo epoxidation.