Solvent effects on oxygen-17 chemical shifts in methyl formate: Linear solvation shift relationships

A multiple linear regression analysis has been carried out using the Kamlet -Abboud-Taft solvatochromic parameters in order to quantify the solvent eff ects on the O-17 chemical shifts of methyl formate (MF). The influence of t he solvents upon the carbonyl oxygen chemical shifts is smaller for MF than for N-methylformamide (NMF). The influence (in parts per million) of the s olvent polarity-polarizability reduces from -21.9 pi* in amides to -9.6 pi* in MF. The influence of the solvent hydrogen-bond-donor acidities reduces from -42.0 alpha in formamides to -16.9 alpha in MF. The solvent effects up on the dicoordinated oxygen chemical shifts of MF are smaller in magnitude and opposite in direction, i.e., 4.8 pi* and 2.6 alpha, than those for the carbonyl oxygen. O-17 hydration shifts have been calculated for the NMF + ( H2O)(6) and MF + (H2O)(5) complexes by the ab initio GIAO method at the 6-3 11 + G** level. The hydration shifts calculated for the carbonyl oxygens of NMF and MF and for the dicoordinated oxygen of MF, - 102.4, -64,7, and 17. 6 ppm, respectively, show the same trend as the corresponding empirical hyd ration shifts, - 101.7, -42.0, and 14.2 ppm. (C) 2001 Academic Press.