A comprehensive overview of the taiwaniaquinoid family of natural products is presented. A summary of the isolation, biosynthesis, and biological activity of these compounds is followed by a discussion of various synthetic strategies to the skeletal framework and a detailed discussion of 12 published syntheses of members of this family. This review covers the literature from the discovery of the first taiwaniaquinoid in 1995 until June 2009.

The taiwaniaquinoids: a review.

The equilibrium isotope effects (EIE) for the one-electron transfer between pyrene and seven regioselectively deuteriated pyrene isotopic isomers in dimethylformamide with 0.1 M tetrabutylammonium hexafluorophosphate were measured electrochemically. These data correlate linearly with the free energies (ΔG°) obtained in tetrahydrofuran using electron paramagnetic resonance (EPR) techniques. However, the slope of the resulting line is not unity, and it indicates that the EIE in the DMF system is only two-thirds of that in the THF system. PM3 calculated ΔG°'s, which would correspond to the gas phase electron transfers, also correlate linearly with both sets of experimental data, but the predicted magnitudes of the EIE's are smaller than those observed experimentally by either technique. The nonunity slopes probably reflect slight differences in ion solvation and/or ion association parameters between the anion radicals of the isotopic isomers. No general relationship between the EIE and the charge on the hydr...

Relative solution electron affinities of selectively deuterated pyrenes: correlations between voltammetric, electron paramagnetic resonance, and semiemperical PM3 data

Appreciable 14N/15N equilibrium isotope effect has been observed for the electron-transfer process between N,N,N‘,N‘-tetramethyl-p-phenylenediamine (TMPD) and its radical cation perchlorate (TMPD+•...

14N/15N Isotope Effect on the Electron Transfer Process between N,N,N‘,N‘-Tetramethyl-p-phenylenediamine and Wurster's Blue

Ion-molecule chemistry

14n/15n isotope effect on the electron transfer process between phenothiazine and its radical cation

Ion cyclotron resonance and electron spin resonance have been utilized to determine the equilibrium constant for the electron transfer from the nitrobenzene anion radical to VN labeled nitrobenzene (Ph UNO2 + Ph VNO2 in equilibrium Ph UNO2 + Ph VNO2Z. It was found that the equilibrium constant is within experimental error of unity at 305 K. Molecular orbital calculations indicate that this might be accounted for by the shortening of the C-N bond and a counterbalancing lengthening of the N-O bonds upon electron attachment to nitrobenzene. An equilibrium constant that is much larger than unity can be observed in liquid ammonia at 208 K when K serves as the gegenion (K/sub eq/ = 2.1). However, when Na serves as the gegenion, the solution electron affinity of Ph UNO2 is greater than that of Ph VNO2 (K/sub eq/ = 0.4). These results are explained in terms of ion association. When the hydrogen atoms are replaced with deuteriums, the gas phase electron affinity is decreased. A similar decrease is observed in liquid ammonia. In the gas phase this is attributed to the slight lengthening of all the C-H bonds upon electron attachment.

Matthew E. Espe

Papers

Effect of isotopic substitution upon the gas phase and solution electron affinities of nitrobenzene

Effect of Isotopic Substitution Upon the Gas Phase and Solution Electron Affinities of Nitrobenzene.