13C Substituent chemical shifts of the carbonyl sites in the side-chains of meta-and para-substituted benzenes of the type XC,H,COZ have been measured. Analysis of this data using the dual substituent parameter method shows that inductive effects are predominant, The reverse inductive contribution observed is explained in terms of a xpolarization mechanism. Critical support for this mechanism is obtained from additional series where the carbonyl is complexed with Lewis acids. The concepts of ' extended ' and ' localized ' n-polarization are discussed. -2.23 -0.

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As proton concentration increases, the first two reversible (1 e-)-reduction processes of the anion α-[S2Mo18O62]4- in 95/5 MeCN/H2O convert to an overall (2 e-)-reduction process. Half-wave potentials for reversible one-electron reduction of [S2Mo18O62]4- itself and its two one-electron-reduced forms [S2Mo18O62]5- and [HS2Mo18O64]4- were estimated by voltammetry to be 0.12, −0.13, and 0.35 V, respectively, versus the ferrocenium/ferrocene couple. Simulation of cyclic voltammograms provided estimates of association constants of 1.4, 1.6 × 108, and 102 M-1 for protonation of the respective products of the reductions, [S2Mo18O62]5-, [S2Mo18O62]6-, and [HS2Mo18O62]5-. Equilibrium constants for disproportionation of the (1 e-)-reduced species were derived. Rates of the electron transfer and protonation processes are very fast relative to the voltammetric time scale. Consideration of the equilibrium constants, plus information obtained from acid titrations monitored by steady state voltammetry, helped define conditions for the isolation of salts of the (1 e-)-, (2 e-)-, (2 e-, 1 H+)-, (2 e-, 2 H+)-, (4 e-, 2 H+)- and (4 e-, 4 H+)-reduced derivatives of the [S2Mo18O62]4- anion. Anions at the (6 e-)- and (8 e-)-reduced levels undergo spontaneous oxidation in the acid solutions and could not be isolated experimentally. The present work shows that directed synthesis of reduced species in different protonation states is possible for these complex systems if adequate voltammetric data are available.