A direct low-temperature carbon-13 and fluorine-19 nuclear magnetic resonance study of boron trifluoride complexes with pyridines

Abstract

Complexes of boron trifluoride with a series of substituted pyridines have been studied using a direct, lowtemperature 13C and '9F n.m.r. technique. At temperatures from 0 to -40 "C, ligand exchange is slow enough to permit the observation of separate 13C n.m.r. signals for bulk and co-ordinated pyridine molecules. The co-ordinated pyridine shift displacements are interpreted in terms of ligand polarization and a paramagnetic effect at the nitrogen atom. The BF3 19F n.m.r. chemical shifts were correlated with calorimetric data in several cases, and in general provide a measure of the strength of the interaction but not of ligand basicity. Comparative complexing abilities were evaluated by studying several pyridine mixtures.

Speciation of Basic Nitrogen Compounds in Gas Oils and Vacuum Gas Oils by Derivatization with BF3 prior to NMR Analysis

“…The results given in bold have been obtained in this study, and the other results have been obtained by Fratiello et al…”

“…This hindrance effect seems to impact also chemical shifts since they follow the same order. Considering the work of Fratiello et al, the chemical shifts depend mainly on the strength of the interaction between the nitrogen and the boron atoms . Actually, this interaction depends both on the Lewis basicity of the nitrogen atom and on the hindrance.…”

“…In the literature, the derivatization by BF 3 , characterized by 19 F NMR, has already been used to indirectly measure the Lewis basicity of organic compounds or to identify structures of nitrogen − and oxygenated − adducts. However, to our knowledge, BF 3 has never been used as derivatization agent to characterize nitrogen compounds in feedstocks.…”

Modelling nucleophilic substitution at silicon in solution, using hypervalent silicon compounds based on 2-pyridones

“…However, compared to the 1-alkyl-2-pyridone, a similar pattern is observed when boron trifluoride complexes with 2-methoxypyridine. 16 Small deviations from the line are observed which may arise from experimental error, specific interactions within the model compound or a non-linear response of the chemical shift to the extent of bond formation. In each case the % Si-O bond formation has been estimated to give the best fit to the complete set of data.…”

“…The 13 C chemical shifts of the ring carbons are similar to those of 2-methoxypyridinium salts. 16 The only drawback with using 10 as the limiting case is that compound 2 with 100% Si-O bond formation involves formation of a five membered ring. This may lead to geometry changes in the aromatic ring that are not present in compound 10.…”