NUCLEOPHILIC-SUBSTITUTION IN PVC - ADDITIONAL NMR PROOF OF THE CONFORMATIONAL MECHANISM

By utilizing some new C-13-NMR spectra of very high resolution, the contents of mm, mr and rr triads and of mmmm, mmmr and rmmr pentads of PVC after nucleophilic substitution to various degrees (ranging between 0 and 10%) could be measured very accurately. Moreover, the content of mmmmrx (x = m, r) and rmmmrx (x = m, r) isotactic heptads could be estimated semiquantitatively. The evolution of these bands allows both to confirm that the reaction proceeds preferably by mm triads, as already found in earlier work, and to assess that only mm triads in ...mmr... sequences are reactive and that the reactivity is higher as the length of the isotactic sequence ending with mmr increases. These results support the conformational mechanism of substitution proposed earlier.