Model building initial molecular models

The reaction of bromine with cyclohexene involves anti addition, which generates, initially, the diaxial conformation of the addition product that then undergoes a ring flip to the diequatorial conformation of rn r-l,2-dibromo-cyclohexane. However, when the unsaturated bicyclic compound I is the alkene, instead of cyclohexene, the addition product is exclusively in a stable diaxial conformation. Account for this. (You may find it helpful to build handheld molecular models.)... 

The initial functions taken for the starting point in the model-building process are called basis functions. We shall use this terminology henceforth. The reason for introducing a new term instead of just continuing to call the starting functions atomic orbitals is that molecular orbitals can themselves serve as starting functions in an interaction model. 

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