Butane, bond distances conformational energies

One-electron oxidation of alkanes leads to a-radical cations (equation 5.55). ° Such ionization removes an electron from an orbital associated with cr bonding among carbon atoms. The radical cation of butane, for example, shows elongation of the C2-C3 bond to a distance of about 2.0 A and a much lower difference in energies of the anti and gauche conformers than is the case with the parent hydrocarbon. Ionization of methane... 

The energy of butane as a function of the dihedral angle about the bond between carbons 2 and 3.The lowest energy conformation occurs when the two methyl groups are the maximum distance apart 9 = 180°). The highest energy conformation occurs when the two methyl groups are eclipsed (9 = 0°). 

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