The torsional potential function for n‐butane

The energies of four different conformations for n ‐butane were calculated by the ab initio method using an STO‐3G basis set. Fully relaxed molecular geometries obtained from molecular mechanics (MM2) were used. The two energy minima [anti ( C 2h ), gauche ( C 2 )] and the two maxima ( C 2 , C 2v ) had the following relative energies: 0.0, 0.88, 3.56, 5.99 kcal/mole. These are approximate Hartree–Fock numbers. It is estimated that inclusion of electron correlation in the calculation would lower the last number to about 5.1 kcal/mole while leaving the first three values essentially unchanged.