Pauli exchange steric repulsion

NBO analysis has been used to dissect the contributions of the three principal contributors to ethane s structural preferences and separate steric and hyperconjugative interactions. It was found that removal of vicinal hyperconjugation interactions yields the eclipsed structure as the preferred conformation, whereas Pauli exchange (steric) and electrostatic (Coulombic) repulsions have no decisive influence on the preference for a staggered conformation. The hyperconjugative preference for the staggered conformation is attributed to the antiperiplanar stereoelectronic requirement sununarized in Figure 6.5. 

EX Exchange energy. Part of the interaction energy between static charge clouds of two subunits, resulting from Pauli exchange between them. Similar to steric repulsion for molecular interactions. 

The major barrier forming steric (Pauli exchange) repulsion changes are given for fully relaxed rotation in the six... 

Section 5.3) of steric effects which compared Pauli exchange repulsions for fully relaxed and rigid rotations, we now partition the fully relaxed barrier energy, AE. into partially relaxed energy terms ... 

---