1,721,010 research outputs found
Volumetric Properties of Dilute Aqueous Solutions of Poly(ethylene Glycols)
No full textThe densities of aqueous solutions of some poly(ethylene glycols) (mono-, di-, tri-, and tetraethylene glycol, and four carbowaxes with a mean molecular weight ranging from 600 to 15,000), and of di-, tri-, and tetraethylene glycol dimethyl ether have been determined at 25°C, in the concentration range 5–100 g/liter. From these data, the limiting partial specific and/or molar volume of the solute has been calculated. A value of 37.0 ml/monomole has been evaluated for the partial molar volume of the repeating unit CH2CH2O, and has been found independent of both terminal groups and chain length. The results suggest that the ethylene units in higher polymers are accessible to the solvent as easily as in oligomers, and support an “open” or extended conformation of the poly(ethylene glycol) chain in aqueous dilute solution. This interpretation has been confirmed by a comparison of the experimental values of partial molar volume with the values calculated by semiempirical models
Volume Changes In the Proton Ionization of Omega-aminocarboxylic Acids In Aqueous-solution
No full text
Thermodynamic Study of Dilute Aqueous-solutions of Organic-compounds .5. Open-chain Saturated Bifunctional Compounds
No full textValues have been determined at 25°C of the changes in the free energy, enthalpy and entropy corresponding to the process of transfer from the ideal gas state to dilute aqueous solution for ethylene-diamine, 2-methoxyethylamine, 3-methoxypropylamine, 1,2-dimethoxymethane and four 2-alkoxy-ethanols (methoxy to n-butoxy).
These data have been used to calculate the variations in the thermodynamic functions of hydration for the hypothetical process of introducing a Y group (Y = O, NH) into a monofunctional RX compound (X = O, NH, NH2, OH), either by breaking a C—C or a C—H bond. Evidence of strong interactions between hydrophilic centres in bifunctional compounds emerges. The strength and nature (entropic or enthalpic) of these interactions depend on both the type of functional groups and their relative distance
Discriminating Interactions Between Chiral Molecules In the Liquid-phase - Effect On Volumetric Properties
Full text linkVolume changes on mixing for binary mixtures of optically active liquid compounds have been determined
at 25 "C by using a vibrating tube densimeter. Six enantiomeric and six nonenantiomeric pairs of chiral molecules
have been considered. In all the cases chiral discrimination appeared to produce small but significant effects
(0.0024.016 cm3 mol-'). The excess molar volumes, p, of the (+) and (-) isomers of limonene, carvone,
2-methyl-1-butanol, and a-methylbenzylamine showed negative values, while VE of the enantiomers of a-pinene
and 2-odanol gave positive results. Partial molar volumes, Po,fo r the investigated chiral solutes in chiral solvents
have been obtained from p data. The effecta of chiral discrimination of Po have been compared with the
prediction of a simple statistical approach in which discrimination arises from space-filling differences in contacts
between hard surfaces
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