Determination of the Quadrupolar Coupling Constant and the Asymmetry Parameter of Oxygen‐17 in Acetone by ¹⁷O‐ and ¹H‐NMR in Nematic Phases

Abstract

SummaryLinear relationships between the inverse of the quadrupolar coupling constant, 1 /x and the asymmetry parameter r] are obtained for the '70-nucleus of acetone oriented in four different nematic phases, using the information contained in 'H-and I70-NMR spectra. The absence of a unique intersecting point of these relations shows that the quadrupolar constants differ slightly between polar and apolar nematic phases, while the orientation remains similar. By combination of the experimentally derived relations with predictions from the theory of Townes and Dailey, values for x = 11.15 MHz and r] = 0.47 in polar media and x = 11.35 MHz and = 0.51 in an apolar medium are obtained, which are similar to those found in the gas and solid phases.Introduction. -Direct determination of quadrupolar coupling constants for I7O is usually performed in the solid state by nuclear quadrupole resonance (NQR) [l-81 or in the gas phase by microwave spectroscopy [9] [lo]. In isotropic liquids, an indirect method based on quadrupolar relaxation yields the quadrupolar coupling constant from the linewidth of the I70-NMR signal, using the asymmetry parameter predicted by theory [ll]. In this work, a method based on the orientation of host molecules by nematic phases is used. This technique has been applied to the I4N-and *H-nuclei [12], but not yet to the '70-nucleus. Knowledge of the quadrupolar coupling constants and the asymmetry parameter gives an insight into the electronic repartition in a molecule and provides a test for the theoretical calculations of molecular orbitals and electric field gradients [13] [14].

Oxygen-17 NMR spectroscopy: Basic principles and applications (part II)

“…Chim. Acta [700] Table 185. The satellites are often too broad to be observed (observation of satellite transitions under MAS can be achieved if the quadrupolar interaction is small, e.g.…”

“…Copyright 1984, by Swiss Chemical Society.) Table 186 17 O quadrupolar coupling constant, v, and asymmetry parameter, g, with corresponding Pp (population of the oxygen atomic orbital in the carbonyl p-bond) obtained by combining the experimental relations determined in four nematic phases with the Townes-Dailey theory [700]. Adapted, with permission, from Helv.…”

“…However, no such point was found presumably due to the slight variation of the v( 17 O) values from one phase to another, resulting from the effect of the high polarity and solvation ability of the medium. The authors [700] attempted to quantify this variation by comparing the experimental relations with semi-empirical calculations using the Townes and Dailey approximation (Fig. 189, Table 186).…”

Dielectric Behavior of Some Small Ketones as Ideal Polar Molecules

“…The 3τ r values for Ac and 3P in the pure liquid state were determined from the experimental T 1 ( 17 O NMR) values measured by the inversion−recovery pulse sequence via eq 5 assuming parameters of κ = 0.5 and NQCC = 11.3 ± 0.1 MHz evaluated for acetone. 30 The temperature dependencies of the 3τ r values determined for 17 O of Ac and 3P are also shown in Figures 4(a) and (b). The agreements between the 3τ r and τ μ values for both Ac and 3P appear to be perfect.…”

“…The temperature dependencies of ηT −1 that resulted from the viscosity measurements and the 3τ r values determined from the 17 O NMR T 1 measurements for 4H are also plotted in Figure 10. The parameters κ and NQCC necessary to calculate τ r are assumed to be the same as those of acetone, 30 as in the case of Ac and 3P. Both the ηT −1 and 3τ r data show Arrheniustype temperature dependencies over the entire examined T −1 range, with activation energies, E η * and E r *, that are identical to the value of E d * = 12.3 kJ•mol −1 for τ μ1 in the low T −1 range.…”