CORRELATION OF O-17 SUBSTITUENT-INDUCED CHEMICAL-SHIFTS - META-SUBSTITUTED AND PARA-SUBSTITUTED METHYL BENZOATES

Oxygen-17 NMR spectra of 45 substituted methyl benzoates in acetonitrile were measured at natural abundance. The substituent-induced chemical shifts (SCS) of the carbonyl oxygen correlate well with the sigma(m) and sigma(p)+ substituent constants in two separate correlations for meta and para derivatives; principal component analysis (PCA) is only slightly better [particularly for the N(CH3)2 substituent]. The O-17 SCS generally depend on the same factors as the C-13 SCS of the beta-carbon of alkenes, provided comparison is made between compounds of similar polarity. SCS of the methoxyl oxygen depend less precisely on sigma(m) or sigma(p), with some unexplained deviations.