Singlet-triplet energy separation states

Table 1 Spin preference of ground state and the calculated singlet-triplet energy separation of some selected Jt-conjugated diradicals...

It is well known that double bonds have a different effect on the singlet-triplet energy separation and thus on the reactivity of the carbene than alkyl groups. The description of the electronic structure of such carbenes is rendered more difficult by the fact that several low-lying electronic states are possible. For... 

The chemistry of phosphinidene and phosphenium systems continues to be an active area. The electronic configurations of vinylnitrene and vinylphosphinidene have been compared in a theoretical study, which predicts that both have triplet ground states. A triplet ground state is also found for phenylphosphinidine, whose properties are very similar to those of methylphosphinidene. A theoretical consideration of factors affecting the singlet-triplet energy separation in phosphinidenes has concluded that the singlet state is favoured by substituents... 

Figure 7. Fine structure constants D, hyperfine structure constants A, activation energies of the thermal reaction and singlet triplet energy separation of the dlradlcal and dlcarbene triplet states. There is a characteristic change of all properties when the structure changes from diradicals to dlcarbenes.

In contrast, the B state can be described with one CSF, and the HF wavefunction is thus expected to be a reasonable approximation to the correct wavefunction. As a consequence, HF theory treats the triplet and singlet states of methylene in an unbalanced way. The triplet state is described better than the singlet state, resulting in singlet-triplet energy separations which are too large. 

Fig. 30 (a) Experimental and calculated (TD-B3P86/6-311G(d)) singlet-triplet energy gaps, AESX, for the charge separated states,... 

Figure 4. Transient states and interconversion pathways for porphyrin-futlerene dyads. The solid bars represent energies for free-base porphyrin-fullerene dyad 26, and the dashed bars represent energies for the zinc-porphyrin-fullerene dyad. Solid bars represent singlet or charge-separated states, and hollow bars stand for triplet states. The energies of the charge-separated states refer to polar solvents.

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