E. Del Rio et al., On the structure of phenonium ions: The important role of back-bonding interaction in carbocation chemistry, J PHYS CH A, 104(23), 2000, pp. 5568-5571
Binding in phenonium ions [C6H5-C-2(OH)(4)](+), [C6H5-C-2(CH3)(4)](+), [C6H
5-C2F4](+), [p-NC-C6H4-C2H4](+), [p-OHC-C6H4-C2H4](+), [C6H5-C2H4](+), [p-F
-C6H4-C2H4](+), [p-H3C-C6H4-C2H4](+) [p-HO-C6H4-C2H4](+), [C6H5-C-2(CHO)(4)
](+), and [C6H5-C-2(CN)(4)](+) was investigated with the B3LYP/6-31G* metho
d. The analysis of the Kohn-Sham orbitals and a Bader analysis of the compu
ted electron density of the phenonium ion, [C6H5-C2H4](+), clearly show tha
t back-bonding from the phenyl cation moiety to the ethylene fragment deter
mines the formation of the three-membered cycle, rendering the shielding of
the ipso carbon atom similar to that for an sp(3) C, while an extension of
the conjugation occurs as both pi systems merge with each other. The impor
tant stabilization gained from this process determines the orthogonal confo
rmation of the phenonium ion.