Cyclohexane, axial bonds conformational analysis

X-ray analysis has shown that cyclodecane in its most preferred conformation exists as shown below in which the two chain forms of cyclohexane are joined by 1,3 axial bonds and six hydrogen atoms are intraannular and 14 peripheral. 

Conformations of Cyclobutane and Cyclopentane Conformations of Cyclohexane 127 Axial and Equatorial Bonds in Cyclohexane 129 Conformational Mobility of Cyclohexane 131 Conformations of Monosubstituted Cyclohexanes Conformational Analysis of Disubstituted Cyclohexanes Boat Cyclohexane 140 Conformations of Polycyclic Molecules 141... 

The analysis of H and C data, particularly H chemical shifts and C-H coupling constants, is indeed often used to determine C-H bond orientation. In cyclohexane, / C-H coupling constants of equatorial C-H bonds ( /c-Heq) greater than those of axial bonds ( /c-Hax) (the Perlin effect). This effect also operates in 1,3-dioxanes for the C-2 position protons <73ACS2676>. In contrast, the C-5 position protons display a reverse Perlin effect when the conformation is locked by a 2-t-butyl substituent <94JCS(P2)ii5i>. Such a reverse Perlin effect has been observed for all ring protons in... 

Aspects of cyclohexane conformational analysis. A. Interconverting chair forms of cyclohexane, with axial and equatorial locations labeled. In the left structure letters x are axial while letters y are equatorial. Note that the chair flip moves axial substituents to the equatorial position and vice versa. B. Newman projections down the C1-C2/ C5-C4 bonds of methylcyclohexane. In the axial form, there is a gauche butane interaction between the methyl and C3. C. Views of cyclohexane, equatorial methylcyclohexane, and axial methylcyclohexane. Note that chair cyclohexane is a relatively disk-shaped molecule, and an equatorial methyl does little to disrupt this shape. In contrast, an axial substituent puts a "kink" into the structure. Also evident is the steric interaction between one methyl hydrogen and the two axial hydrogens on C3 and C5. 

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