A-stabilization energies

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. 

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)... 

Figure 5.14 Correlation of net H-bond energy (A2shb, squares) and principal n-a stabilization energy (AEn a,(2), circles) with intermolecular charge transfer (Qcr) cf. Table 5.15. (Approximate trend-lines are shown for each quantity to aid visualization.)...

Theoretical calculations predict that the highest occupied Walsh orbital of the cyclopropene ring in 1 should stabilize a positive charge at C2, ° and this prediction was experimentally confirmed. Appearance energy measurements for the loss of Br from ionized 2-bromobenzocyclopropene (202 X = Br) suggest that the benzo-cyclopropen-2-ylium ion 291 is stabilized by more than 27.6 kcal/mol over the phenyl cation 292. Calculations (3-2IG ) give a stabilization energy of 23 and 22 kcal/mol of 291 over 292 and over the m-isomer 293, respectively. ... 

DMDO epoxidation of cyclohexene (Table 5) is rednced by 4.1 kcalmoD when a single water molecule is hydrogen-bonded to the distal oxygen of DMDO (a bimolecular process relative to a prereaction clnster of DMDO, H2O) and by 6.3 kcalmoD with two complexed water molecules [B3LYP/6-311+G(d,p)]. The H-bonded DMDO-CH3OH prereaction cluster has a stabilization energy of —6.9 kcalmoD. The calculated barriers for the DMDO epoxidation of -2-butene with and without water catalysis are 11.0 and... 

Exercise 21-7 1,3-Butadiene has a substantial stabilization energy, whereas ethene has none, yet attack of Br on 1,3-butadiene occurs more readily than on ethene. Explain how 1,3-butadiene can have a stabilization energy greater than ethene but still be more reactive toward reagents that donate Br ... 

Exercise 21-8 The experimental —AH0 (25°C) is 707.7 kcal for combustion of one mole of gaseous 1,3-cyclopentadiene to liquid water and carbon dioxide. From this value compute a stabilization energy for cyclopentadiene with the aid of the heat of vaporization of water (10 kcal mole-1) and any required bond energies. Show your... 

Let us start by looking at these four-coordinate geometries. The a stabilization energy, (o), derived using Eq. (6) and the energy-level... 

Figure 2.3 Schematic representation of CT transitions. EA(A) = electron affinity of species A IP(B) = ionization potential of species B A = stabilization energy of AB. Adapted from ref [19],...

Various molecular orbital calculations " provide plausible stabilization energies for cyclopropenone. Photoacoustic and bomb calorimetry have provided the heat of formation of diphenylcyclopropenone as 350 16 and 354 + 21 kJ mol respectively, which leads to a stabilization energy of 46kJmol In contrast, the physical and spectroscopic properties of the cyclopropenones have been explained without recourse to aromatic stabilization, but this is contrary to what is generally accepted. 

Table 4 Results of B3LYP calculations for the position of energy minima, (in A), stabilization energies, AE (in cm ), and force constants, K (in eV/A ), for several electronic...

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