Comment on "A quantitative definition of hypervalency" by M. C. Durrant, , 2015, , 6614.

Consideration is given to (electronically) hypervalent increased-valence structures, which possess 2c-1e bonds, fractional 2c-2e bonds, and usually normal 2c-2e bonds. For singlet-spin electron-rich systems, increased-valence structures, with Heitler-London 2c-2e bond wavefunctions, are equivalent to resonance between non-hypervalent Kekulé and Dewar (or singlet diradical) type Lewis structures. Dewar structures are not considered in the 2015, , 6614 Edge article on hypervalency. Using one-electron delocalizations from lone-pair atomic orbitals into separate bonding molecular orbitals, increased-valence structures for PCl, O, SO, NO, NO and S2 reactions are derived from the Edge-article's Kekulé-type Lewis structures, and compared with the Edge article's hypervalent structures with 2c-2e bonds. It is also shown that Durrant's method to determine the parameter for -type systems that possess a symmetrical 3c-4e bonding unit is related to the -atom charge density.