Triplet structure isomers

Polarization Transfers and Reaction Mechanisms. Polarization transfers include the previously mentioned electron-nuclear Over-hauser effect and the nuclear-nuclear Overhauser effect. In this section we will discuss only electron-electron polarization transfer via a secondary chemical reaction involving a primary polarized radical. Again we shall use the photoreduction of quinone (t-butyl-p-benzoquinone) as an example. In solvent containing isopropanol, reaction of triplet quinone by phenols leads to two structural isomers, radicals I and II ... 

In 1987 we reported26 that the three possible C3H2 isomers S-2, T-36, and S-37 can be transformed into each other under photochemical conditions. For several reasons propargylene (36) attracted our attention On the one hand the first C3H2 parent species, identified by direct spectroscopic methods, was triplet propargylene (T-36). Its ESR spectrum was published in 1965,63 and, based on the zero-field-splitting parameters, a linear or nearly linear structure was derived. On the other hand, the structural elucidation of 36 by comparison of the calculated and experimental IR spectra turned out to be rather difficult.64... 

In the lower triplet state, the silabenzene molecule retains its planar structure whose energy is higher by 107 kcal/mol than that of the structure of the singlet ground state (STO-3G) (78JA6499). Like benzene, silabenzene is more stable than its isomers (259)—(262) by, respectively, 38.4,... 

The integrated difference of majority and minority spin electronic charges, denoted by M, is given in column 3 of Table 4. The spectroscopic multiplicity of the complex is M +1. We see that for MA complexes Au O with even (odd) n, that is, with odd (even) number of electrons, the minimum energy isomer is a doublet (triplet). These M +l values coincide with the ones found by Yoon and coworkers , except for 4c and 7b structures, where these authors obtained M =3 and M =2, respectively. Note that these two cases are the only MA complexes with significant different values compared to our results. 

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