CORRELATION-ANALYSIS OF P-31 NMR CHEMICAL-SHIFTS WITH SUBSTITUENT EFFECTS OF PHENOLS

Over 60 lignin-related model compounds were phosphitylated with 2-chloro-4,4,5,5-tetramethyldioxaphospholane, a sterically hindered analogue of 2-chloro-1,3,2-dioxaphospholane used in earlier work, and their P-31 chemical shifts were recorded. Excellent resolution between the chemical shifts of phosphitylated carboxylic acids, phenols and aliphatic alcohols was obtained. The correlations of the phosphorus chemical shifts with the chemical environments of lignin-related phenols using the Hammett principles provided an excellent linear relationship between the resonance substituent constant, sigma(R)(0), and the corresponding P-31 NMR chemical shift values for para-substituted lignin-related phenols. In addition, a correlation between P-31 NMR chemical shifts for ortho- and para-substituted phosphitylated phenols was obtained, A set of empirical parameters that permits the accurate prediction of P-31 NMR chemical shifts of lignin-related phenolic compounds derivatized with 2-chloro-4,4,5,5-tetramethyldioxaphospholane was thus obtained.