An NMR study of the structure and reactivity of phosphonium ylides stabilized by a carbonyl function

The structures of five stabilized phosphonium ylides 1 - 5 were studied by 1 H, 13 C, and 31 P NMR. Various trapping experiments were followed by investigation of the relative reactivities of these ylides vis-à-vis benzaldehyde. A novel effect of some significance, the influence of acidic contaminants (conjugate acids, H 2 O, etc.) on the structure and reactivity of these compounds, is discussed. Key words: stabilized phosphoranes, Wittig condensations, acid catalysis.