 The three hydrogens at each end are free to pinwheel about the central carbon-carbon bond, provided that there is sufficient energy to overcome the barrier of the carbon-hydrogen bonds at each end of the molecule bumping into each other by way of overlap (exchange) repulsion.Also at Harvard, Pitzer also helped formulate the perturbed Hartree–Fock equations in a form for calculating the effects of external electric and magnetic fields on molecules.He was a postdoctoral fellow at M.I.T.