Triplet electronic configuration

The experimental evidence is clear that, not only is the cation not stabilized in the same way as the anion, it also has a triplet electronic configuration. These facts agree with the molecular orbitals of Figure 21-13 for a cyclic system with five p orbitals, and also with the An + 2 rule, because 34 has six 77 electrons, whereas 35 has only four. 

In contrast, the following should be unstable with 4n tt electrons and triplet electronic configurations ... 

The carbene thus reacts with O2 to form an orffio-benzoquinone O-oxide, and with an aliphatic alcohol as H-donor to form a phenoxyl radical (plus an aliphatic radical not shown in Scheme 1). The ground state triplet electronic configuration of this carbene accounts for its reaction behavior, in particular for the fact that it reacts very slowly with the solvent, H2O. In agreement with the intrinsically faster intersystem crossing of 2-bromophenol compared to 2-chlorophenol, the quantum yield of the carbene pathway was higher for the former = 0.04) than for the latter compound (< = 0.003). In contrast, the quantum yields of photo contraction were comparable (< = 0.04). The transient absorption data were confirmed by photoproduct analysis, showing the formation of phenol from 4-bromophenol in the presence of H-donors [16]. 

Fig. 2.1. Schematic representation of the electron distribution over the MO s for open shells in the restricted (RHF) and unrestricted Hartree-Fock (UHF) methods (D stands for doublet and T for triplet electronic configuration)...

A sufficiently comprehensive classification of the radical reactions has been suggested in Ref [2]. Regarding the structure of electron shells of the reactants, the radical reactions are subdivided into two classes. The first of these comprises the reactions in which the common electron shell is closed or has a triplet electron configuration (2n electrons), i.e., the reactions of recombination and those of radical pair and biradical formation. To the second class (free-radical reactions) the transformations belong in which one of the reactants has a closed shell and the other—one unpaired electron (total number of electrons is 2n + 1). 

Scheme 8 Electron configuration and polarization in the triplet diradicals...

As well known, the methylene lowest state is a triplet, with electronic configuration (Ifli) (2ai) (162) (3 i) (l ), which lies somewhat below the fundamental singlet state, Mj. In addition, the companion singlet state, fii, is also known. To... 

Figure 2 Different electronic configurations arising from the relative strengths of orbital overlap (AE) and pairing energy (PE) AE > PE favours a closed-shell diamagnetic singlet (a) whereas AE

Fig. 13 Qualitative molecular orbital energy level diagram of the dimer d orbitals with the 14 electrons showing the electronic configuration 525 27i47i 4o2 (singlet) and the first excited state 828 2it4it 4a1CT 1 (triplet)...

It is found that triplet (S = l) is the ground state for a linear Fe-O-O conformation, with the same electronic configuration as found for the open-shell singlet ... 

The minimum of the triplet state corresponds to a larger Fe-O-O angle (131°) than the S = 1 state (121°), as we also found for a small FeP(Im)(02) system [6b]. On the other hand, an S = 0 closed-shell state is well separated in energy in the linear conformation (22 kcal mol-1 relative to the ground triplet state), but becomes very close to the ground state in the bent conformation (1.4 kcal mob1). Its electronic configuration can be shown schematically as ... 

Most stable ground-state molecules contain closed-shell electron configurations with a completely filled valence shell in which all molecular orbitals are doubly occupied or empty. Radicals, on the other hand, have an odd number of electrons and are therefore paramagnetic species. Electron paramagnetic resonance (EPR), sometimes called electron spin resonance (ESR), is a spectroscopic technique used to study species with one or more unpaired electrons, such as those found in free radicals, triplets (in the solid phase) and some inorganic complexes of transition-metal ions. 

Specific examples are now used to demonstrate these concepts. First, consider the group Ru(bpy)j2+ (luminescent), Os(bpy)32+ (slightly luminescent), and Fe(bpy)32+ (nonluminescent) (Table4.1). For Fe(bpy)32+, despite an exhaustive search no emission has ever been detected even at 77K we routinely use it as a nonemissive solution filter. All three iso structural eft systems are in the same oxidation state with the same electronic configuration (ft6). The Fe(II) complex has an intense MLCT band at 510 nm, and the Ru(II) complex at 450 nm the Os(II) complex has intense MLCT bands that stretch out to 700 nm. The n-n transitions are all quite similar in all three complexes with intense absorptions around 290 nm and ligand triplet states at 450 nm (inferred from the free ligand and other emissive complexes and the insensitivity of these states to coordination to different metals). 

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