Water electric moment

These calculations are of special interest because Purcell and coworkers have been interested in the structure-activity relationships of this series of compounds for several years and have compared several approaches to structure-activity relationships with the same compounds. Earlier they (27, 28) reported on detailed studies of the effect of partition coefficients (benzene-water), electric moments, and electronic structures on the relative activity of the congeners. Purcell (28) used Huckel molecular orbital theory to calculate the net charges on all the atoms of each compound. The only apparent success was the apparent correlation of the net charge at the amide nitrogen atom with activity. This was later shown to be caused by the statistically significant correlation between the 7T value and the net charge on the nitrogen atom (29). 

The existence of this residual entropy of ice at very low temperatures was discovered by Giauque and Ashley (ref. 7), who preliminarily ascribed it to the persistence of rotation of ortho-water molecules (comprising 3/< of the total) about their electric-moment axes, giving an entropy of 3/ R In 2 = 1.03 E. U. 

The "stickiness shown by water is not found in small molecules without permanent electric moments. Their mobility within crystals is governed much more by the openness of the frameworks, modified by the siting of the cations, which may partially obscure the window apertures. 

In order to account for the high dielectric constant of water it is necessary to suppose that there exist groups of molecules with a pseudocrystalline structure, that is, with sufficient orientation of the O-H-0 bonds to give an appreciable electric moment. The upper limit of size of these clusters has been estimated from studies of the infrared absorption bands in the 1-1-1-3 /ii region as approximately 130 molecules at 0°, 90 at 20°, and 60 at 72°C. In a liquid there is constant rearrangement of the molecules, and it is postulated that a given cluster persists only for a very short time, possibly of the order of 10 to 10 seconds. 

Measurements of electric moments have been much used in connection with problems of molecular structure. An excellent summary of the conclusions in that field has been published by Sidgwick.24 Certain questions can be decided from the presence or absence of an electric moment. Thus water, which has the comparatively large moment of 1.842 X 10 18, must have an unsymmetrical structure. Three possible arrangements are ... 

The orientational structure of water near a metal surface has obvious consequences for the electrostatic potential across an interface, since any orientational anisotropy creates an electric field that interacts with the metal electrons. The anisotropy of the orientational distribution of water has therefore been investigated in most studies of aqueous systems in inhomogeneous environments. The results can be summarized as follows. In almost all studied systems, a preference for orientations in which the water dipole moment is more or less parallel to the interface has been observed. The driving force for the avoidance of orientations that can lead to surface electrostatic... 

Liquid with pungent odor. bp7 81.4. tig 1.4086. dj 0.8636 dj5 0 8407. Easily soluble in water, methanol, ethanol, ether, acetone, glacial acetic acid. Slightly sol in hydrocarbons. Forms a binary azeotrope with water, bp 75 (12% water), uv spectrum and electric moments Rogers, J. Am. Chem. Soc. 69, 2544 (1947). Polymerizes on standing, LDm in mioe and rats 35 mg/kg, C.A. 72, 124809b 0970). 

In chapter i we discussed the interaction between two widely separated water molecules and concluded that it could conveniently be treated in terms of (i) the interaction between the permanent electric moments of the molecules, (ii) the polarization or delocalization terms due to the distortion of the electron cloud of one molecule by the field of the other, (iii) dispersion forces having their origin in co-ordinated electronic motion in the two molecules, and (iv) the repulsion due to the action of the Pauli exclusion principle when the two electron clouds begin to overlap. Most calculations of the cohesive energy of the ice crystal amount to an evaluation of these contributions for more or less realistic models. Among these it is convenient to distinguish two different types ... 

The shift in the point of zero charge in the case of the adsorption of an organic substance is usually associated with the change in the electric moment of the surface layer upon the substitution of the dipoles of the organic substance for the oriented water dipoles. This change may be due to other causes as well, e.g., to a change in the potential distribution in the electronic cloud at the metal surface [3]. 

Theoreticians did little to improve their case by proposing yet more complicated and obviously unreUable parameter schemes. For example, it is usual to call the C2 axis of the water molecule the z-axis. The molecule doesn t care, it must have the same energy, electric dipole moment and enthalpy of formation no matter how we label the axes. I have to tell you that some of the more esoteric versions of extended Hiickel theory did not satisfy this simple criterion. It proved possible to calculate different physical properties depending on the arbitrary choice of coordinate system. 

The Hydrolysis of Salts. As shown in Table 41, the NH,i molecule has a dipole moment almost as large as that of the H20 molecule. When ammonia has been dissolved in water the electrostatic interaction of an NH3 dipole with an adjacent solvent dipole is of the same order of magnitude as the interaction between two adjacent H20 dipoles. At the same time, when ammonia has been dissolved in water, the solution has a feeble electrical conductivity, due to the fact that a certain... 

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