Hydrogens equatorial

Equatorial halide is gauche to axial and equatorial hydrogens on adjacent carbon cannot undergo anti elimination in this conformation... 

FIGURE 1.6 The two chair conformations of cyclohexane a = axial hydrogen atom and e = equatorial hydrogen atom. 

Figure 4.8 Axial (red) and equatorial (blue) positions in chair cyclohexane. The six axial hydrogens are parallel to the ring axis, and the six equatorial hydrogens are in a band around the ring equator.

With the radical 29, even though loss of an equatorial hydrogen should be sterically less hindered and is favored thermodynamically (by relief of 1,3 interactions of the axial methyl), there is an 8-fold preference for loss of the axial hydrogen (at 100 ( i. The selectivity observed in the disproportionation of this and other substituted cyclohexyl radicals led Beckwith18 to propose that disproportionation is subject to stereoelectronic control which results in preferential breaking of the C-H bond which has best overlap with the orbital bearing the unpaired spin. 

Oxygen moves away from equatorial hydrogens no torsional strain... 

Equatorial hydrogens the hydrogen atoms lie around the perimeter of the ring of carbon atoms. 

Not much information is available for the five-membered ring pyrrolidine (4). MM2 calculations predicted that the 2-half-chair form is preferred over a host of other conformers by an average of 0.3 kealmol-1 with a 4.37 kealmol-1 barrier to planarity. The equatorial hydrogen is calculated to be favored by AE = 0.20 kealmol-1 over the axial one. 

For example, cyclohexane gives a single averaged resonance in the H NMR at room temperature, but separate signals are seen for the axial and equatorial hydrogens when spectra are acquired at very low temperature. 

Correspondingly, the interconversion of the twist-boat intermediate into the other chair form can be viewed as rotation about the opposite ring bond. Overall, two independent bond rotations , pausing at the high-energy (but stable) twist-boat intermediate, effect conversion of one chair structure into another equivalent chair, and at the same time switch axial and equatorial hydrogens. 

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