Study of interactions between Brønsted acids and triethylphosphine oxide in solution by ³¹P NMR: evidence for 2 : 1 species

Abstract

The variation of the 31P chemical shift of triethylphosphine oxide (TEPO) in CDCl3 solution with a series of Brønsted acids at different molar ratios allows to determine the value for...

Phosphine oxides as NMR and IR spectroscopic probes for the estimation of the geometry and energy of PO⋯H–A hydrogen bonds

“…As mentioned in the Introduction section, recently several attempts to employ dP for the hydrogen bond characterization have been published. 52,69,[73][74][75] Practically in every case the authors saw significant potential in dP, but in order to estimate the robustness of this parameter and establish the limits of its applicability further studies seem to be necessary. In the case of complexes studied here, as can be seen in Fig.…”

“…15 shows the correlations between DdP and the pK a values of phenols, alcohols, carboxylic acids and benzoic acids considered in this work (filled symbols) and collected from ref. [73][74][75] for OH acids with one OH group (open symbols). Though there is significant scattering of data points, a linear correlation is held for each class of proton donors.…”

“…71,72 However, over the last few years several experimental papers have been devoted to Brønsted acidity exclusively. [73][74][75][76] These papers share the same essential approach; the proton-donating abilities of Brønsted acids, measured as the corresponding pK a values (in water), were correlated with the change of dP of a trialkylphosphine oxide upon complexation. In all cases, despite the significant scattering of data points that occurs sometimes, linear correlations were observed (see, for example, Fig.…”

What Is Being Measured with P-Bearing NMR Probe Molecules Adsorbed on Zeolites?

“…Moreover, TMPO interacts with Brønsted and Lewis acid sites, giving 31 P NMR chemical shifts ranging from ∼53 to 86 ppm and from ∼55 to 60 ppm, respectively. , However, the interpretation of 31 P NMR spectra of TMPO-loaded zeolites remains controversial. While some authors contend that TMPO interaction with Brønsted and Lewis acid sites gives rise to 31 P NMR resonances in distinct spectral regions, , others argue that they overlap. , Furthermore, recent studies show that two TMPO molecules may gather at the same acid site, forming (TMPO) 2 H + dimers. , The diversity of TMPO binding modes further hinders our understanding of the nature of the TMPO–acid interaction in microporous materials, requiring the tandem use of spectroscopic and computational tools.…”

Solid State NMR for Nonexperts: An Overview of Simple but General Practical Methods

“…For example, 31 P NMR has been used to elucidate thermal and hydration effects on the mobility of compact, branched, and bulky pharmaceutical molecules loaded in submonolayer amounts onto mesoporous silica [102]. Great progress has been achieved in our understanding of the effects of noncovalent interactions on the 31 P chemical shift of P=O groups [26,103,104]. However, P=O groups can form two noncovalent interactions simultaneously [105][106][107].…”