Electron Donation in the Water–Water Hydrogen Bond

Donation is not from an sp3 orbital: Decomposition analysis, based on absolutely localized molecular orbitals, provides an alternative and somewhat unconventional view of hydrogen bonding in the water dimer. A new description of the electron-donating orbital is uncovered: unlike sp3 lone pairs, a single donor–acceptor orbital pair forms, in which the donating orbital changes its orientation according to the relative positions of the two molecules.