Bromocyclohexane, conformational equilibria

Look at Figure 4.12, and estimate the percentages of axial and equatorial conformers present at equilibrium in bromocyclohexane. 

One major difference between cyclic and acyclic systems is the inability of cyclic systems to undergo rotation about carbon-carbon bonds, leading to relatively well-defined conformations. If trans-A-tert-h ity - -bromocyclohexane is used as an example, there is the usual equilibrating population of the two chair conformations (sec. 1.5.D). The diequatorial conformer is significantly more stable and accounts for the major portion of the equilibrium (sec. 1.5.B). According to Corey s calculations from Section 1.5.D, the equatorial form predominates (>99.99 <1, diequatorial/diaxial). To predict the major product, nucleophilic backside attack on both conformations must be considered, and the less sterically hindered pathway is usually preferred. In this case, the diequatorial conformation is more reactive. 

---