Stabilization energies, estimates

Pyrrole is believed to be more aromatic than furan, with an aromatic stabilization energy estimated to be 100-130 kj mole-1, thus only with such extremely powerful dienophiles as tetrakis(trifluoromethyl)Dewar thiophene were the IEDA adducts isolated. Therefore, several attempts to achieve an IEDAR with pyrroles using high pressure have been made [9-14]. 

Fig. 20-32. Dissociation energies of the hexammines of some divalent metal ions. Solid circles are the total energies. Open circles are the total energies minus the ligand field stabilization energies estimated from spectroscopically derived A0 values.

Harmonic Oscillator Stabilization Energy Estimation of Canonical Structure Weights and Stabilization Energy from Bond Lengths... 

Basis set effect on hydrogen bond stabilization energy estimation of the Watson-Crick type nucleic acid base pairs using medium-size basis sets single point MP2... 

We might be hard pressed to estimate the individual resonance stabilization energies in Eqs. (7.23) and (7.24), but the qualitative apphcation of these ideas is not difficult. Consider once again the styrene-vinyl acetate system ... 

Benson17 has tried to collect some thermodynamic data based on a number of empirical rules for this class of radicals. He estimated heats of formation for HS02, MeSO 2) PhSO 2 and HOSO 2 as —42, —55, —37 and — 98kcalmor respectively. He also estimated a stabilization energy for the benzenesulfonyl radical of 14 kcal mol"1, which is very similar to that of the benzyl radical. However, recent kinetic studies18 (vide infra) have shown that arenesulfonyls are not appreciably stabilized relative to alkanesulfonyl radicals, in accord with the ESR studies. 

Using results from the DFT calculations, combined with databases of segregation energies, estimate the stability of the alloys in working reaction environments. 

In order to compare the structural options for transition metal compounds and to estimate which of them are most favorable energetically, the ligand field stabilization energy (LFSE) is a useful parameter. This is defined as the difference between the repulsion energy of the bonding electrons toward the d electrons as compared to a notional repulsion energy that would exist if the d electron distribution were spherical. 

It was expected that participation of the dipolar forms b in the ground-state hybrid of 7/8 might introduce the special electronic stability of the delocalized 2 tr-configura-tion to compensate for the high strain energy estimated for these molecules, (e.g. 8 ... 

Of the 17 kcal mol-1 total error, about half is estimated to arise from the single hp— h[ j sigma-type interaction shown in Fig. 2.8, while the remainder arises from weaker pi-type interactions (2-3 kcal mol-1 each). For example, we can carry out a partially localized variational calculation, similar to that described above but with only h prevented from delocalizing into tip (hisleads to a stabilization energy (at 7 = 1.6 A)... 

Sigma- and pi-type donor acceptor interactions Further details of the leading hp —hM donor-acceptor interactions are gathered in Table 2.5 and Figure 2.21. For each such interaction the table shows the hybrid form of the donor (hp)23 and acceptor (hM) orbitals, the occupancy of the acceptor, and the second-order estimate (cf. Eq. (1.35) or (2.7)) of the donor-acceptor stabilization energy. Let us now discuss some of the trends displayed in Table 2.5. 

Figure 3.62 Leading n-

Figure 3.65 The prototypical no-uco anomeric donor-acceptor interaction in dihydroxymethane (estimated second-order stabilization energy 14.43 kcal...

Figure 4.40 Hyperconjugative ctwh->-0 wc interaction in FHWfCO) (cf. Fig. 4.38(a)), with estimated second-order stabilization energy 11.6 kcal mol-1.

Figure 4.62 Ti- H2 donor-acceptor interactions at R = 1.8 A (with estimated second-order stabilization energies in parentheses) (a) o-HH nTi and (b)...

Figure 5.25 The strongest (innermost) nF->- ohf interactions in (HF) chain (a)-(c) and cyclic (d) clusters (cf. Fig. 5.23), with estimated second-order stabilization energies in parentheses. These innermost interactions best approximate the limiting case of an infinite cyclic structure.

---