The electronic structure of 1,3-dipoles: hypervalent atoms

Abstract

Spin–coupled theory is applied to the π electrons of the 1,3-dipoles diazomethane, fulminic acid, and nitrone, and to the inorganic molecules O₃, N₂O, and NO₂. The linear molecules are treated as planar species, in the spirit of 1,3-dipoles taking part in cycloaddition reactions as systems with four π electrons. A very simple, albeit unexpected picture arises for the bonding in these π-electron systems. The central nitrogen atom in CH₂N₂, for example, takes part in five covalent bonds. We use the label ‘hypervalent’ for such a situation, and we identify hypervalent atoms in all of the molecules considered. We discuss the consequences of our model for the chemistry and properties of 1,3-dipoles.