Hueckel molecular orbital .pi. resonance energies. New approach

Abstract

the neutral base must approach closer to the Sn2 center than the charged base for the same extent of CH3F distortion, C-F (leaving) charge buildup and bond weakening, and C-base bond formation.

Graph Theory of Aromatic Stabilization

“…16 The TRE concept was devised with the images of DRE and HSRE in mind. As will be seen, TREs calculated for a variety of cyclic conjugated hydrocarbons are compared favorably with their respective DREs and HSREs.…”

“…Hess and Schaad employed eight parameters to reproduce the total π-binding energy of acyclic polyene. 16 They argued that the 'polyene' π-bond energy depends not only on the bond type but also on the bonding status of the conjugated atoms. Normal π-bond energies for eight types of CC π-bonds 16 are listed in Table 2.…”

“…16 They argued that the 'polyene' π-bond energy depends not only on the bond type but also on the bonding status of the conjugated atoms. Normal π-bond energies for eight types of CC π-bonds 16 are listed in Table 2. The definition of HSRE is similar to that of DRE in eq 1:…”

“…TREs and HSREs are a kind of vertical ASE, in the sense that they are calculated on the assumption that a polyene-like reference π-system has exactly the same geometry as a real π-system. 16,25,26 By contrast, DRE is a kind of adiabatic ASE, since additive bond energies used to estimate the energy of a polyene-like reference are those derived from bond-alternating acyclic polyenes. 6 In general, bond lengths in acyclic polyenes are different from those in aromatic π-systems.…”

“…16,17 In fact, SSE(LA) is consistently 1020% larger than TRE, probably because circuits larger than length-six are counted doubly or multiply. 113 As can be seen from Figure 31, the following least-squares line was obtained between TRE and SSE(LA) for 20 familiar PAHs:…”