Localized orbitals for NH₃, C₂H₄, and C₂H₂

Localized orbitals were obtained for NH₃, C₂H ₄, and C₂H₂ by the Lennard-Jones and Pople criterion of minimizing the interorbital and maximizing the intraorbital Coulomb and exchange energy. Orbitals conforming to the chemical-bonding picture (an inner shell, three N-H bonds and a lone pair) were obtained for pyramidal NH₃. "Bent bonds" were obtained for planar NH₃. In the cases of C₂H₄ and C₂H₂ there are the usual inner shells and C-H bond orbitals (the latter being bent for twisted ethylene), while the C-C bonds are equivalent "banana orbitals," two for the ethylene double bond and three for the acetylene triple bond. Some cases of nonuniqueness of the localized-orbital description are discussed.