Water Debye units

Figure 4 shows the measured angle of 105° between the hydrogens and the direction of the dipole moment. The measured dipole moment of water is 1.844 debye (a debye unit is 3.336 x 10 ° C m). The dipole moment of water is responsible for its distinctive properties in the Hquid state. The O—H bond length within the H2O molecule is 0.96 x 10 ° m. Dipole—dipole interaction between two water molecules forms a hydrogen bond, which is electrostatic in nature. The lower part of Figure 4 (not to the same scale) shows the measured H-bond distance of 2.76 x 10 ° m or 0.276 nm. 

The dipole moment is a fundamental property of a molecule (or any dipole unit) in which two opposite charges are separated by a distance . This entity is commonly measured in debye units (symbolized by D), equal to 3.33564 X 10 coulomb-meters, in SI units). Since the net dipole moment of a molecule is equal to the vectorial sum of the individual bond moments, the dipole moment provides valuable information on the structure and electrical properties of that molecule. The dipole moment can be determined by use of the Debye equation for total polarization. Examples of dipole moments (in the gas phase) are water (1.854 D), ammonia (1.471 D), nitromethane (3.46 D), imidazole (3.8 D), toluene (0.375 D), and pyrimidine (2.334 D). Even symmetrical molecules will have a small, but measurable dipole moment, due to centrifugal distortion effects. Methane " for example, has a value of about 5.4 X 10 D. 

Water can interact with ionic or polar substances and may destroy their crystal lattices. Since the resulting hydrated ions are more stable than the crystal lattice, solvation results. Water has a very high dielectric constant (80 Debye units [D] versus 21 D for acetone), which counteracts the electrostatic attraction of ions, thus favoring further hydration. The dielectric constant of a medium can be defined as a dimensionless ratio of forces the force acting between two charges in a vacuum and the force between the same two charges in the medium or solvent. According to Coulomb s law. 

The Herbicide Handbook, 2002 or the Pesticide Manual, 1994. Water Air Soil Pollut., 86 389-405. dIn Debye units, as measured in dioxane at 20°C. eNA Not available. 

The situation was viewed at first as somewhat surprising since, in such interactions, considered to be essentially ion-dipole interactions, the molecule with the larger dipole moment, water (p = 1.85 debye units) should have been taken up preferentially to ammonia (n = 1.47). 

Pyrazine forms an azeotrope with water [60% pyrazine-40% water, b.p. 95.5° (uncorr.) (760mmHg) /ip 1.4510] (578). A method of assay for pyrazine and some common impurities has been developed (579). The dipole moment (Debye units) of pyrazine has been determined in dioxane, cyclohexane, and benzene as zero (580, cf. 581) and it has also been calculated as zero (133, 582). The e.s.r. spectrum (583) and the polarized single-crystal absorption spectra of pyrazine (and tetramethylpyrazine) (584) have been recorded. The photoelectron spectra of pyrazine and tetramethylpyrazine have been determined and suggest a different behavior towards electrophilic attack in the two cases (585). 

A stig — dielectric increment per gm. protein per liter /r = dipole moment in debye units t H O is the relaxation time in water at 25° (correcting for the relative viscosity of water and the solvent actually employed) To = relaxation time of a sphere, of volume equal to that of the protein, in water at 25° ajb = ratio of major to minor axis, calculated from r and observed relaxation times, by the equations of Perrin (92) [Cohn and Edsall (Jd)], neglecting hydration. 

It is sometimes stated that measurement of dipole moments is a discriminating test for the detection of zwitterions, which, it is supposed, should have a dipole moment of at least 15 D (Debye units) as compared with a maximum of 6 5 D for a highly dipolar (but non-ionized) molecule such as p-nitroaniline. This was found not to be true for a series of aromatic zwitterions whose dipole moments were measured in dioxan (Serjeant, 1964). For example, a substance which was found to be over 90% zwitterionic in water had a dipole moment in dioxan differing by only O 18 D from that of the corresponding ester (both... 

We discuss the rotational dynamics of water molecules in terms of the time correlation functions, Ciit) = (P [cos 0 (it)]) (/ = 1, 2), where Pi is the /th Legendre polynomial, cos 0 (it) = U (0) U (it), u [, Is a unit vector along the water dipole (HOH bisector), and U2 is a unit vector along an OH bond. Infrared spectroscopy probes Ci(it), and deuterium NMR probes According to the Debye model (Brownian rotational motion), both... 

The dipole moment p. is a molecular property defined as the product of charge (usually just a fraction of the electronic change, of course) and distance between the centers of positive and negative charge in the molecule. The dipole moment is usually expressed in debyes (D), where 1 D = 1(T esu in SI units 1 D = 3.3356 X 10 ° C-m. so, for example, the dipole moment of water is 1.84 D or 6.14 in units of 10 C-m. Again a rough correspondence is seen between this property of a molecule and its polarity, though e and p. are not precisely correlated. 

B. Protein Solutions. The dielectric properties of proteins and nucleic acids have been extensively reviewed (10, 11). Protein solutions exhibit three major dispersion ranges. One occurs at RF s and is believed to arise from molecular rotation in the applied electric field. Typical characteristic frequencies range from about 1 to 10 MHz, depending on the protein size. Dipole moments are of the order of 200-500 Debyes and low-frequency increments of dielectric permittivity vary between 1 and 10 units/g protein/100 ml of solution. The high-frequency dielectric permittivity of this dispersion is lower than that of water because of the low dielectric permittivity of the protein leading to a high-frequency decrement of the order of 1 unit/g protein/... 

This extraction precisely reproduces the same London, Debye, and Keesom interactions, including all relativistic retardation terms that had been effortfully derived in earlier formulations. These interactions are distinguished by whether they involve the interaction of two permanent dipoles of moment //.uipoie, or involve an inducible polarizability aind. A water molecule, for example, has both a permanent dipole moment and inducible polarizability. The contribution of each water molecule to the total dielectric response is a sum of the form of Eqs. (L2.163) and (L2.173) in mks units,... 

Fig. 16. Resonance scattering of erbium ions incorporated in the water phase (20%) of di-palmitoyl diphospatidyl cholin (DPPC) near the L3 absorption edge of erbium at X, = 1.482 A) The intenity units are proportional to the number of photons per ring of the Debye-Scherrer diagramme...

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