Three-Electron Two-Center Bonding in Cycloimmonium Ylides

摘要

We explore the possibility that a 3-electron-2-center bonding exists in cycloimmonium ylides.To detect this bonding in a polyatomic system,3-electron-l-hole density operators,characterizing a Pauling 3-electron bond,are used in the framework of second quantization formalism.The weights of 3-electron resonance structures are calculated and compared with the weights of 2-electron structures for the ylide bond of pyridinium dicyanomethylide; the correlations of(arrow up arrow down)and(arrow up)electronic events,involved in the 3-electron resonance structures,are also investigated.The calculations are performed in various approximation levels,and both orthogonal and nonorthogonal natural atomic orbitals are adopted.All calculations show that a 3-electron bond exists between N and C atoms of ylide bond,but this bonding is not extended in C atoms of the pyridinium group.The interactions of alpha,beta electrons(at the configuration interaction[CI]level)increase the localization of electrons,the weights of 3-electron resonance structures,and thus the probability for 3-electron bonding.