Thennal shift

Electron transfer processes, more generally transitions that involve charge reorganization in dielectric solvents, are thus shown to fall within the general category of shifted harmonic oscillator models for the thennal enviromnent that were discussed at length in Chapter 12. This is a result of linear dielectric response theory, which moreover implies that the dielectric response frequency a>s does not depend on the electronic charge distribution, namely on the electronic state. This rationalizes the result (16.59) of the dielectric theoiy of electron transfer, which is identical to the rate (12.69) obtained from what we now find to be an equivalent spin-boson model. 

The second step, which yields vitamin D3, is a thennal [1,7] sigmatropic shift of a hydrogen atom. Based on the symmetry of the HOMO of a heptatrienyl system, the transfer of the hydrogen must occur antarafacially. Both the number of single bonds and the number of atoms provide sufficient ffexibihty for this reaction to occur. 

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