Acoustical absorption spectra between 10 kHz and 2 GHz are reported for various monosaccharides in water. With the exception of solutions of methyl-␤-D-arabinopyranoside ͑0.5 mol/l͒ the spectra reveal absorption with relaxation characteristics in excess to the asymptotic high frequency absorption term. Up to three relaxation terms per spectrum emerge within the measuring frequency range. Regression analysis of the measured spectra in terms of a suitable analytical spectral function yields five relaxation regimes with relaxation times on the order of 1 s, 100 ns, 10 ns, 1 ns, or 100 ps, respectively. These relaxation regimes are assigned to the chair-chair ring inversion, two modes of pseudorotation, an exocyclic side group isomerization and a molecular association mechanism. Particular emphasis is given to the ring inversion which is additionally verified by time resolved measurements of nonequilibrium tautomer systems, utilizing the coupling of the inversion to the carbohydrate mutarotation. Further evidence is derived from measurements of solutions of D-fructose in mixtures of ethanol and water.

Molecular relaxation properties of sodium dodecylsulfate in aqueous solutions with surfactant concentrations between 0.009 and 0.4 mol/L have been studied using broadband ultrasonic spectrometry in the frequency range 0.1-2000 MHz. Ultrasonic excess attenuation characteristics were found that could be well represented by a sum of three relaxation terms, each one characterized by a discrete relaxation time. The low-frequency term with concentration-dependent relaxation time, tau1, between 0.06 and 3.5 micros is discussed in terms of the surfactant monomer exchange. The noticeable effect from the incomplete dissociation of the surfactant counter ions and the variation of the monomer concentration following thereby is discussed. The second relaxation term (0.9

Ultrasonic resonator cells for liquid attenuation and sound velocity measurements down to 70 kHz are described. The resonators are provided with easy-to-obtain concavely shaped shaving mirrors as acoustic reflectors and separated piezoelectric devices for the coupling of the cell to the electronic set-up. The advantages of this construction are shown. The mode spectrum of the resonators is discussed and measurement and evaluation procedures, also considering higher-order satellite peaks, are presented. Possible sources of experimental errors are specified and examples of measurements are given to illustrate the favourable performance of the cell design.

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Broadband acoustical spectrometry (10 kHz ≤ ν ≤ 5 GHz) of aqueous solutions of monosaccharides at thermal equilibrium are reported as well as time-resolved acoustical attenuation and optical activity measurements of saccharide solutions during approach of their tautomer equilibrium from nonequilibrium concentrations. The existence of the chair−chair conformational flexibility is shown. Its presence depends on the anomeric form, reflecting the balance of axial and equatorial hydroxy groups of the saccharide ring, as predicted theoretically. For the widely used d-fructose, the time constant of the anomer equilibrium (0.05 min-1, 20 °C) has been determined acoustically. Relaxation time and activation enthalpy of the ring conformational isomerization are 1 × 10-6 s and 42 kJ/mol, respectively, at 25 °C.