High level ab initio energies and structures for the rotamers of 1,3-butadiene.

High level ab initio calculations, utilizing coupled cluster theory with quasi-perturbative triple excitations and augmented quadruple zeta level basis sets, have been used to determine the structures and relative energies of the four stationary points on the 1,3-butadiene torsional potential curve. Corrections were applied in order to minimize the residual basis set error, as well as account for core/valence correlation and scalar relativistic effects. Higher order correlation recovery was also included to improve our estimate of the relative energies. The transition state separating the trans and gauche rotamers lies 26.8 kJ/mol above the trans global minimum. The gauche rotamer lies 12.6 kJ/mol above the trans rotamer and the s-cis form is a transition state 2.0 kJ/mol higher than the gauche rotamer (excluding zero point energies).