Structural and spectroscopic differences among the potassium 5-hydroxypentanoyltrifluoroborate salt and the furoyl and isonicotinoyl salts

Abstract

FT-IR, FT-Raman and ultravioletevisible spectroscopies were used to characterize the potassium 5-hydroxypentanoyltrifluoroborate salt (HTFB) while the theoretical structures of this salt in gas andaqueous solution phases were studied by using hybrid B3LYP/6-311þþG** calculations and the selfconsistent reaction field (SCRF) and solvation (SM) models because these models consider the solventeffects. Good concordance were obtained among the predicted 1H-, 13C and 19F-NMR chemical shifts forHTFB in aqueous solution with the corresponding experimental available data for this salt in CDCl3. Thecorrected solvation energy by using ZPVE and non electrostatic terms is higher for this salt (103.73 kJ/mol) than those reported for furoyl (84.72 kJ/mol) and isonicotinoyl (95.05 kJ/mol). Evidently, the sidechain in HTFB increase the solubility of this salt in water, as compared with furoyl and isonicotinoyl. TheNBO analyses show that the potassium 2-isonicotinoyltrifluorborate salt in both media is most stablethan hydroxypentanoyl and furoyl salts and, in particular, the side chain in HTFB generates a diminishingof its stability in aqueous solution. Probably, this low stability of HTFB in solution is due to the highersolvation energy and to the n/s* transitions no observed in the other salts. The AIM studies support thehigh stability of isonicotinoyl than the other two salts and, also, reveal the ionic characteristics of theKe--O and Ke--F interactions observed in those three salts. The comparisons of the gap values for thethree species suggest that the most reactive salt is isonicotinoyl while furoyl salt is the less reactive. Thedescriptors show the importance of study these salts in different media because the values in solutionare slightly different in the three salts from those computed in gas phase. In addition, the harmonic forcefields and the scaled internal force constants for the salt in both media are reported together to theircomplete vibrational assignments.