NMR OF TERMINAL OXYGEN .7. O-17 NMR-SPECTRA OF BENZOYL DERIVATIVES OF GE, SE, TE AND I - PI-BOND ORDER AND EXCITATION-ENERGY IN BENZOYL COMPOUNDS

The benzoyl derivatives of SeR, TeR and I show lower field O-17 NMR signals than those of the lighter elements in the same group of the Periodic Table, whereas ArCOGeR3 is as low-field as ArCOSiR3. The delta-O values of 14 types of benzoyl compounds ArCOX are discussed in terms of pi-bond order (obtained from arene substituent sensitivities using the 'tool of increasing electron demand') and of electronic excitation energy (obtained from UV spectra). It is concluded that, for O-17 NMR, the terms DELTA-E-1 and SIGMA-Q of the Karplus-Pople equation are, at least to a certain degree, independent of one another.