Valence-bond model radicals

Figure 2.21. The composition of the adsorbate orbitals of symmetry in a perturbational treatment for N2 adsorbed on Ni. Polarization is achieved through intergroup and intragroup mixing. In terms of a valence bonding model, this can be seen as the partial breaking of the N2tt bond, forming nitrogen radicals. From Ref. [3].

R. Mereau, M. T. Rayez, J. C. Rayez, P. C. Hiberty, Phys. Chem. Chem. Phys. 3, 3650 (2001). Alkoxyl Radical Decomposition Explained by a Valence Bond Model. 

Evaluated In a photoionization mass spectrometric study from the difference in the thresholds for PHJ from PH3 and PHJ from PHg [1 ]. This value is only 4 kJ/mol higher than the almost coincident values calculated with the 4th-order Moller-Plesset perturbation procedure [1, 8] and with the generalized valence bond model [9]. - From the electron impact ionization of PH3 and PHg. - From the fluorescence excitation of PH3 photolysis fragments. - From the appearance potential of PHJ in electron impact studies of PH3 and the ionization potential of PHg. - From the appearance potential of PH2 from PH3 (2.2,2.3 eV) and the electron affinity of the PH2 radical (1.25 eV, see p. 62) [5] for earlier results (D<326 kJ/mol), see [10]. - From the highest populated rotational-vibrational level of HF, which is produced in a hydrogen abstraction reaction of PH3 with F atoms in a flowing afterglow experiment [6] for earlier results, see [11]. - Literature value based on the upper limit D<326 kJ/mol. 

Valence-bond models of bonding in (a) benzyl cation, (W benzyl radical, and (c) benzyl anion. Overlap of the 2p orbital of the benzylic carbon with the IT system of the benzene ring creates an extended n system that stabilizes each one by electron delocalization. 

Alkoxy Radical Decomposition Explained by a Valence Bond Model. 

Linnett used the concept that an octet of valence shell electrons consists of two sets of four opposite-spin electrons to show that in diatomic and other linear molecules the two tetrahedra are not in general formed into four pairs as we have discussed for F2 and the CC triple bond in C2H2. This idea is the basis of the double-quartet model, which Linnett applied to describe the bonding in a variety of molecules. It is particularly useful for the description of the bonding in radicals, including in particular the oxygen molecule, which has two unpaired electrons and is therefore paramagnetic This unusual property is not explained by the Lewis structure... 

Figure 6-21 Atomic-orbital model, valence-bond structures, and resonance-hybrid formula for the 2-propenyl radical...

In the valence-bond (VB) model, this effect results from the fact that radicals of this type can be stabilized by resonance (Table 1.1, right). In the MO model, the stabilization of radical centers of this type is due to the overlap of the n system of the unsaturated substituent with the 2pz AO at the radical center (Figure 1.5). This overlap is called conjugation. 

Ponthieux S, Paulmier C (2000) Selenium-Stabilized Carbanions.208 113-142 Raimondi M, Cooper DL (1999) Ab Initio Modern Valence Bond Theory. 203 105-120 RenaudP (2000) Radical Reactions Using Selenium Precursors.208 81-112 Roeggen I (1999) Extended Geminal Models. 203 89-103... 

Unlike thiophene radical cation the SOMO for this species is 2bl with considerable spin density on sulfur. The reversible electrochemical oxidation potentials for 129 and some of its derivatives in l,l,l,3,3,3-hexafluoro-2-propanol are listed in Table 8. The reactions of 129 with radicals and with nucleophiles has been studied [275]. The position of attack by radicals on 129 should reflect the spin density at that position as found by EPR spectroscopic analysis. Indeed reaction with N02 occurs predominantly at S, C(2) and C(4) as expected. The valence bond configuration mixing model leads to the prediction that nucleophiles should preferentially attack 129 at C(l) and C(3) with little attack at S, C(2) and C(4). This is partly but not completely validated experimentally. Radi-... 

A simple valence bond (VB) model was used to account for this chameleon nature of Cpd I, as shown in Figure 2.12 - The electronic structure of Cpd I can be constructed from two resonance structures, a> and b> a> describes a thiolyl radical and a closed-shell iron-oxo porphyrin, while ]b> is an ion pair composed of a thiolate anion and an iron-oxo porphyrin cation... 

To elaborate point (i), we chose thiophene oligomers as model systems [41]. In the present context, it is convenient to characterize the geometry with a single relevant parameter, the inter-ring C-C bond length this bond shortens in radical-cations in agreement with the valence-bond scheme shown in Figure 1.7. The results of ab initio and semiempirical HF spin-restricted open-shell self-consistent field... 

We apply our second-order Ehrenfest method to a model system benzene radical cation. Ionization of the neutral from the degenerate HOMO/HOMO-1 leads to the Jahn-Teller [15] effect in the cation. There is a peaked conical intersection between the two lowest-energy eigenstates Dq and Dy at geometries with D h symmetry. Figure 1 represents the surrounding moat of the conical intersection seen from above. It contains several valence bond (VB) resonance structures three equivalent quinoid structures... 

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