equatorial bond

It is known that axial bonds are more hindered than the corresponding equatorial bonds.

Phosphoranes adopt a trigonal bipyramidal molecular geometry with the two apical bonds longer than the three equatorial bonds.

As can be seen on the model of cyclohexane, the trans configuration comes with a price: the only possible way to join the two six membered rings in the trans position means the second ring needs to start from the two equatorial bonds of the first ring.