NMR of terminal oxygen. Part 7. 17O NMR spectra of benzoyl derivatives of Ge, Se, Te and I: π-bond order and excitation energy in benzoyl compounds

Abstract

The benzoyl derivatives of SeR, TeR and I show lower field ¹⁷O 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 δ_o values of 14 types of benzoyl compounds ArCOX are discussed in terms of π-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 ¹⁷O NMR, the terms ΔE^–1 and ΣQ of the Karplus–Pople equation are, at least to a certain degree, independent of one another.