Alessandro D'Aprano

The static dielectric constant of solutions of water inn-alcohols at 15, 25, 35, and 45°C

Dielectric constants (measured at 1 MHz) are reported for solutions of water (concentration range 0 to 0.2 mole fraction) in 1-propanol at 25°C, and in 1-butanol, 1-pentanol, and 1-hexanol at 15, 25, 35, and 45°C. These results, together with literature values for solutions of water in methanol, ethanol, 1-heptanol, and 1-octanol, show that water interacts with alcohols in at least two ways: (1) it can participate in the formation of dynamic hydrogen-bonded chains, thereby raising the polarizability; (2) it can form relatively stable structures such as H2O(ROH)4 which have zero net dipole moment and consequently diminish volume polarizability. For CnH2n+1OH alcohols,n≥4, most of the initially added water forms complexes: consequently, addition of water to these alcohols lowers the dielectric constant.

Static dielectric constant, viscosity, and structure of pure isomeric pentanols

Static dielectric constants, viscosities, densitites and refractive indices of 2-pentanol, 3-pentanol, 2-methyl-1-butanol, 3-methyl-1-butanol and 2-methyl-2-butanol were measured at 15, 25, 35 and 45°C. These results together with the previous data on n-pentanol have been analyzed in terms of the Kirkwood correlation factor gk and of the energy of activiation for viscous flow. With the exception of 2-methyl-2-butanol, gk was found to be greater than unity. These results show that the monomeric units of isomeric pentanols interact by means of hydrogen bonding to form dynamic structures essentially of two types: linear chains where co-association raises the total polarizability and cyclic dimers with nearly zero net dipole moment. Energies of activation for viscous flow as well as Kirkwood correlation factors correlate with the molecular parameters (i.e. position of OH group in the molecules, steric hindrance of alkyl chain etc.) of the alcohols. The implication of these parameters on the molecular association of the isomeric pentanols are discussed.

Viscosity studies of solutions of water inn-aliphatic alcohols at various temperatures

Viscosity measurements have been made at 25°C on solutions of water inn-propanol, and at 15, 25, 35, and 45°C on solutions of water inn-butanol,n-pentanol, andn-hexanol over the respective solubility ranges. For most of the systems, water decreases the viscosity of the dry alcohols, while for the lower members of the series literature data report an increase in viscosity on addition of water. These results are rationalized in terms of two kinds of interaction between water molecules and alcohols: participation of water molecules in chain formation for the lower alcohols and formation of water-centered complexes for butanol and higher alcohols.

Molecular association and dynamics in n-pentanol and 2-methyl-2-butanol

Static dielectric constant, viscosity, density, ultrasonic and dielectric relaxation measurements are reported for two pentanol isomers (n-pentanol and 2-methyl-2-butanol) in a wide range of temperatures. The results show a different extent of H-bonds self-association in relation to the molecular geometry of the alcohol. The activation energies obtained from dielectric and ultrasonic studies are compared with those obtained from viscous flow. Such a comparison, together with the analysis of all the dielectric and ultrasonic relaxation data, show that in n-pentanol a correlation between viscosity and ultrasonic relaxation exists, while dielectric relaxation is not correlated with the other two processes. This finding has been rationalized in terms of different mechanisms. In 2-methyl-2-butanol a correlation between ultrasonic and dielectric relaxation processes has been observed. Additional contribution of ultrasonic absorption associated with isomeric internal rotational of the molecules has been assumed ...

Conductance in isodielectric mixtures. III.i-butyronitrile with chlorobenzene,o-dichlorobenzene,p-dichlorobenzene, 1,2-dichloroethane, andn-pentanol

The conductance of tetrabutylammonium tetraphenylboride, picrate, perchlorate, and nitrate has been measured at 25°C in mixtures ofi-butyronitrile with chlorobenzene,o-dichlorobenzene,p-dicholorobenzene, 1,2-dichloroethane, andn-pentanol covering the range of dielectric constants 10≤D≤20. In these mixtures of polar solvents, both association constants and ionic mobilities depend on ion-solvent interaction energies and on free volume in a manner that is specific for each system. This failure of the primitive model (rigid charged spheres in a continuum) is shown to be the consequence of short-range spatial and energetic interactions between ions and adjacent solvent molecules.

Velocity and damping of thermal phonons in isomeric alcohols

Polarized Mandelstam-Brillouin scattering data in isomeric pentanols (normal-pentanol and 2-methyl-2-butanol) are presented. Hypersonic velocity νs and absorption α/f 2 are measured as a function of temperature in the liquid phase. The experimental results indicate, for both the alcohols, a shear relaxation phenomenon in the GHz region. The shear relaxation times τs and the shear moduli G ∞, evaluated in the framework of visco-elastic theories, show a temperature dependence characteristic of strongly associated liquids in n-pentanol, whereas a more molecular behaviour is evidenced for 2-methyl-2-butanol.

Conductance of potassium lodide in mixed solvents

The conductance of potassium iodide has been measured in the solvents ethylene carbonate, water, methyl ethyl ketone, and pairwise mixtures of these solvents at 40°C; and ethylene carbonate-water, tetramethylene sulfone-water, dimethyl sulfoxide-water, tetrahydrofuran-water, ethylene carbonate-tetramethylene sulfone-water, ethylene carbonate-tetramethylene sulfone, and tetrahydrofuran-dimethyl sulfoxide at 25°C. For dielectric constants greater than about 60, the pairing constants KA are in the range 0.3–2.0; no correlation between KA and solvent properties could be established. For lower dielectric constants, KA increases exponentially with decreasing dielectric constant. Addition of a proton, acceptor to water initially decreases KA regardless of whether the dielectric constant of the mixture is higher or lower than that of water, suggesting that ion pairs in water may be stabilized by cage structures. The Walden product Aoη is also decreased by the addition of proton acceptors.

Thermodynamics of binary mixtures: Volumes, heat capacities, and dilution enthalpies for then-pentanol+2-methyl-2-butanol system

The densities, heat capacities, and dilution enthalpies ofn-pentanol+2-methyl-2-butanol mixtures have been measured, in many cases as a function of temperature, over the complete mole fraction range. Excesses thermodynamic properties, apparent and partial molar heat capacities, volumes and expansibilities were derived. The concentration and temperature dependences of these functions are discussed in terms of the variations of the structure of the system caused by the participation of the two alcohol molecules (with quite different steric hindrance of the alkyl chain around the-OH group) in the dynamic intermolecular association process through hydrogen bonding.

Molecular interactions in 1-pentanol +2-methyl-2-butanol mixtures: Static dielectric constant, viscosity and refractive index investigations at 5, 25 and 45°C

Static dielectric constants, refractive indices and viscosities of 1-pentanol +2-methyl-2-butanol mixtures were measured at 5, 25 and 45°C. The results show that the mixing of the two isomers modifies the polarizability and the resistence of viscous flow of the system depending on the composition and temperature. Short range intermolecular interactions producing hetero-alcohol open dimers are considered.

Temperature effects on the structure and dynamics of isomeric pentanols by IR and Raman spectroscopy

Abstract We present IR absorption, polarized and depolarized Raman scattering data in n-pentanol and in 2methyl-2butanol. The measurements, performed over a wide temperature range, concern the fundamental O—H stretching vibrations. The experimental results confirm that intermolecular H-bonding effects play the main role in determining the shape and the evolution with T of the spectra. The deconvolution of the polarized Raman spectra in symmetric bands gives useful information concerning the dynamical properties of these systems. The analysis of the frequency shifts, the broadenings and the relative intensity variations with respect to the isolated O—H stretching bands confirm the existence of molecular aggregates with different spatial and/or topological conformations. The close analogy found for appropriately reduced IR absorption and depolarized Raman spectra proves that a vibrational density of states (VDOS) for both alcohols exists. These spectral features can be rationalized in terms of cooperative m...