Singlet migration

It is important to emphasize that the fusion model described by Eq. (2) explicitly neglects the spatial variables of the excitons, an assumption which is strictly valid only when the randomization time is rapid compared to the annihilation rate (12, 1 ). For singlet migration... 

In alicyclic hydrocarbon solvents with aromatic solutes, energy transfer (vide infra) is unimportant and probably all excited solute states are formed on neutralization of solute cations with solute anions, which are formed in the first place by charge migration and scavenging in competition with electron solvent-cation recombination. The yields of naphthalene singlet and triplet excited states at 10 mM concentration solution are comparable and increase in the order cyclopentane, cyclohexane, cyclooctane, and decalin as solvents. Further, the yields of these... 

Hydrogen and 1,2-carbon migrations are the most common singlet carbene rearrangements. They involve simple shifts of substituents from an adjacent carbon to the carbenic center, affording an alkene product Eq. 7. 

We have seen that 1,2-H migrations in singlet carbenes may be affected by (e.g.) the participation of carbene precursor excited states, QMT, stabilization of the hydride shift transition state by polar solvents, and temperature. Here, we consider our third principal theme, the effect of substituents on the kinetics of carbenic rearrangements. We first examine the influence of bystander and spectator substituents (as defined in Eq. 22) on 1,2-H rearrangements of alkyl, alkylchloro, and alkylacetoxycarbenes. 

Spectator substituents, bonded to the carbene s migration terminus (Ci), directly influence the lifetime and philicity of the carbene, but they do not primarily alter the migratory aptitudes of migrants on C2. Oxa spectator substituents stabilize singlet carbenes by electron donation to the vacant carbenic p orbital (LUMO) cf. resonance hybrid 69. 

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