London potential

It is well known that neutral molecules such as alkanes attract one another, mainly through van der Waals forces. Van der Waals forces arise from the rapidly fluctuating dipoles moment (1015 S-1) of a neutral atom, which leads to polarization and consequently to attraction. This is also called the London potential between two atoms in a vacuum, and is given as... 

TRIM is an extremely weak NOS inhibitor. The compound was reported to be 40-fold more selective for nNOS and eNOS over iNOS (Moore, King s College London). Potential for the treatment of chronic pain was suggested, but, as far as we know, no development has been reported since 1997. 

Table 6.1 Contributions of the Keesom, Debye, and London potential energy to the total van der Waals interaction between similar molecules as calculated with Eqs. (6.6), (6.8), and (6.9) using Ctotal = Corient + Cind + Cdisp- They are given in units of 10-79 Jm6. For comparison, the van der Waals coefficient Cexp as derived from the van der Waals equation of state for a gas (P + a/V fj (Vm — b) = RT is tabulated. From the experimentally determined constants a and b the van der Waals coefficient can be calculated with Cexp = 9ab/ (47T21V ) [109] assuming that at very short range the molecules behave like hard core particles. Dipole moments /u, polarizabilities a, and the ionization energies ho of isolated molecules are also listed.

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The van der Waals forces between atoms or molecules are the sum of three different forces, all proportional to 1/r , where r is the distance between the atoms or molecules. The corresponding potentials are the orientation or Keesom potential, the induction or Debye potential, and the dispersion or London potential, respectively. For two dissimilar polar molecules, the van der Waals potential is... 

The remaining interactions in molecules that have permanent dipole moments, that is, the dipole-dipole and dipole-induced-dipole interactions, have the same dependence on intermolecular separation as the London potential, varying as and are of lesser magnitude at ordinary temperatures (Atkins, 1998). These two interactions and the previously mentioned dispersion interaction are collectively known as van der Waals interactions. They are related to such measurable properties as surface tension and energy of vaporization, and to concepts such as the internal pressure, the cohesive energy density (energy of vaporization per unit volume, A UIV), and the solubility parameter, 6, which is the square root of the cohesive energy density (Hildebrand and Scott, 1962). 

Table 2.1 Contributions of the Keesom, Debye, and London potential energy to the total van der Waals interaction between similar molecules as calculated with Eqs. (218),(220), and (2.21) using...

Latimer, W. M. 1952, Oxidation Potentials, Prentice-Hall, Englewood ClifTs, NJ Lednicer, D. Mitscher, L. A. 1977 dt 1980, The Organic Chemistry of Drug Synthesis, Vols. I IT, Wiley New York London... 

Source Values are compiled from the following sources Bard, A. J. Parsons, R. Jordon, J., eds. Standard Potentials in Aqueous Solutions. Dekker New York, 1985 Milazzo, G. Carol , S. Sharma, V. K. Tables of Standard Electrode Potentials. Wiley London, 1978 Swift, E. H. Butler, E. A. Quantitative Measurements and Chemical Equilibria. Freeman New York, 1972. 

R. J. Hunter, Zeta Potential in Colloid Science, Academic Press, Inc., London, 1981. 

T. Hodder, P. Crewther, M. Lett, and co-workers, "Apical Membrane Antigen 1 A potential Malaria Vaccine Candidate," 7th Malaria Meeting of British Society ofParasilolgy, London, Sept. 19—21,1995. 

Forces Molecules are attracted to surfaces as the result of two types of forces dispersion-repulsion forces (also called London or van der Waals forces) such as described by the Lennard-Jones potential for molecule-molecule interactions and electrostatic forces, which exist as the result of a molecule or surface group having a permanent electric dipole or quadrupole moment or net electric charge. 

Investigation of Potential Hazar ds fr om the Oper ations in the Canvey Island/ Thurrock Ar ea, HMSO, London, 1978. Rasmussen, Reactor Safety Study An Assessment of Accident Risk in U.S. Commer cial Nuclear Power Plants, WASH-... 

The Berlin City electrical engineer M. Kallmann reported in 1899 on a system for controlling stray currents of electric railways [64]. As early as 1894, the Board of Trade in London issued a safety regulation for the British electric railways which specified a potential differential of not more than 1.5 V where the pipeline was positive to the rails, but 4.5 V with the rails positive. Extensive research was undertaken on reducing the risk of stray current in the soil by metallic connections from pipes to rails. However, as one writer noted, a procedure on these lines should definitely be discouraged as it carries the seed of its own destruction [64]. 

A multidimensional PES for the reaction (6.45a) has been calculated by Wight et al. [1993] with the aid of the atom-atom potential method combined with the semiempirical London-Eyring-Polanyi-Sato method (see, e.g., Eyring et al. [1983]). Because of high exoergicity, the PES... 

It is prophetic that Firket (1), in speaking about public anxiety about potential catastrophes, said, "This apprehension was quite justified, when we think that proportionately, the public services of London, for example, might be faced with the responsibility of 3200 sudden deaths if such phenomenon occurred there" (p. 1192). In 1952, such a catastrophe occurred (see Section III,C). 

The total van der Waals interaction potential is obtained by simply adding the individual contributions arising from the Keesom, Debye, and London interactions. Because the radial power-law dependencies of all these interactions vary as 1 /r, the total van der Waals interaction can be expressed simply as... 

Potential energy surfaces calculated by means of the London equation (5-15) cannot be highly accurate, but the results have been very useful in disclosing the general shape of the surface and the reaction coordinate. The London equation also forms the basis of some semiempirical methods. 

The semiempirical methods combine experimental data with theory as a way to circumvent the calculational difficulties of pure theory. The first of these methods leads to what are called London-Eyring-Polanyi (LEP) potential energy surfaces. Consider the triatomic ABC system. For any pair of atoms the energy as a function of intermolecular distance r is represented by the Morse equation, Eq. (5-16),... 

We often refer to Heitler and London s method as the valence bond (VB) model. A comparison between the experimental and the valence bond potential energy curves shows excellent agreement at large 7 ab but poor quantitative agreement in the valence region (Table 4.3). The cause of this lies in the method itself the VB model starts from atomic wavefunctions and adds as a perturbation the fact that the electron clouds of the atoms are polarized when the molecule is formed. 

Gatty, O. and Spooner, E. C., Electrode Potential Behaviour of Corroding Metals in Aqueous Solutions, Oxford University Press, London (1938)... 

Neufeld, P. and Queenan, E. D., Frequency Dependence of Polarisation Resistance Measured with Square Wave Alternating Potential , Br. Corros. J., 5, 72-75, March (1970) Fontana, M. G., Corrosion Engineering, 3rd edn., McGraw-Hill, pp 194-8 (1986) Dawson, J. L., Callow, L. M., Hlady, K. and Richardson, J. A., Corrosion Rate Determination By Electrochemical Impedance Measurement , Conf. On-Line Surveillance and Monitoring of Process Plant, London, Society of Chemical Industry (1977)... 

Fig. 21.1 Practical galvanic series of metals and alloys showing potentials on the hydrogen scale. (Note that the potentials shown are typical values that will vary according to the nature of the solution.) (after Butler, G. and Ison, H. C. K., Corrosion and its Prevention in Water, Leonard Hill, London (1966))... 

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