Dielectric Behavior of Some Small Ketones as Ideal Polar Molecules

Abstract

The dielectric behaviors of some small symmetric ketone molecules, including acetone, 3-pentanone, cyclopentanone, 4-heptanone, and cyclohexanone, were investigated as a function of temperature (T) over a wide frequency range from 50 MHz (3.14 × 10(8) s(-1), in angular frequency) to 3 THz (1.88 × 10(13) s(-1)). The temperature dependencies of the rotational diffusion times (τ(r)) determined using (17)O NMR spin-lattice relaxation time (T(1)) measurements and viscosities of the ketones were also examined. The obtained temperature dependencies of the parameters for the ketones were compared with those of ideal polar molecules, which obey the Stokes-Einstein-Debye (SED) relationship without the formation of intermolecular dimeric associations and without orientational correlations between dipoles (molecular axes), that is, free rotation. Kirkwood correlation factors (g(K)) of only acetone and 3-pentanone were close to unity over a wide temperature range, whereas those of other ketones were obviously less than unity. These results revealed that no correlations exist between the rotational motions of dipoles in acetone and 3-pentanone, as expected in ideal polar molecules. However, other ketones exhibited orientational correlations in their dipoles because of dipole-dipole interactions via antiparallel configurations. Furthermore, because acetone and 3-pentanone satisfied the SED relationship and because their microscopic dielectric relaxation times (τ(μ)), which were calculated from the determined dielectric relaxation times (τ(D)) via the relationship τ(μ) = τ(D)g(K)(-1), were identical to 3τ(r) and were proportional to Vη(k(B)T)(-1) over the wide temperature range examined, where V, k(B), and η represent the effective molecular volume, Boltzmann's constant, and the viscosity of the liquid molecules, respectively, these two ketone molecules behave as ideal polar molecules. In addition, other ketones not significantly larger than acetone and 3-pentanone in molecular size likely form dimeric intermolecular associations with antiparallel cyclic configurations, which demonstrates the g(K) values less than unity.

Dielectric Behaviors of Typical Benzene Monosubstitutes, Bromobenzene and Benzonitrile

“…Since the g K factor includes only information related to the rotational relaxation modes, the relationship ε ∞a = ε ∞ + A Dr was assumed for the evaluation of g K values as in the previous study on small ketones . The determined g K values of Br-Bz in the pure liquid state seemed to demonstrate the relationship g K ∼1.0 irrespective of temperature as seen in Figure .…”

“…In particular, the observed DE relaxation time, τ D (or τ μ ), should be controlled by the viscosity of the tested liquid and temperature because polar molecules of g K = 1 show free rotation and feel friction controlled by the Stokes–Einstein–Debye (SED) relationship. We have referred to such polar molecules that satisfy these three criteria of single Debye-type relaxation, g K = 1, and the SED relationship as ideal polar molecules . In our previous study, we investigated the dielectric behavior of some small, symmetric ketones like acetone and 3-pentanone in the pure liquid state at several temperatures and compared the dielectric behavior of the ketones with that of ideal polar molecules .…”

“…The contribution of a difference in the value of dipole moments more than twice to DE behavior should be clearly observed. Especially, the formation of intermolecular associations due to strong dipole–dipole interaction between large dipole moments mainly governs DE behavior of NC-Br without doubt. ,, Nevertheless, the importance of dipole–dipole interaction to the formation of intermolecular associations has not been discussed in detail so far in Br-Bz. If Br-Bz does not make (stable) intermolecular associations because of a not so large dipole moment of 1.72 D, the molecule rotates freely to demonstrate the Debye-type DE relaxation behavior.…”

Solvent Polarity of Cyclic Ketone (Cyclopentanone, Cyclohexanone): Alcohol (Methanol, Ethanol) Renewable Mixed-Solvent Systems for Applications in Pharmaceutical and Chemical Processing

“…53 Cyclopentanone shows peak-splitting phenomena due to self-association 31,52 and Fermi resonance, 54,55 while selfassociation of CPN shows higher possibility to cause the carbonyl peak-splitting phenomena according to DFT calculations 31,52 and dielectric behavior. 56 Nevertheless, the Fermi resonance should have a smaller effect on the fraction of hydrogen bonding (eq 18) than CPN self-association in the mixture. 52…”

Simultaneous neutron powder diffraction and microwave characterisation at elevated temperatures

“…The ratio is significantly higher for acetone compared to water owing to its smaller relative microwave loss, at 20 1C giving a ratio of approximately 20 : 1 as opposed to 4 : 1 for water. 28 If the ambient temperature changes, then the lack of reliable complex dielectric data as a function of temperature in the published literature makes a precise quantitative analysis impossible. We also note that the dielectric properties of bound and free solvents molecules will differ, and again there is a lack of quantitative data in the literature on these different species.…”