NH3 dipole moment

Hydrazine is bound more tightly than ammonia in intercalation compounds with layer disulphides such as TaS2. ° This supports the formulation of these compounds as electron donor-acceptor complexes, as both the dipole moment (1.75 D) and ionization energy (/ = 8.7 eV) of N2H4 indicate that it is a better electron donor than NH3 (dipole moment = 0.58 D, = 10.2 eV). 

NH3 dipole moment in the molecular bond representation. The first global description of the dipole moments of ammonia was reported by Marquardt et al. [66] who computed ab initio DMSs of NH3 using the MP2/ aug-cc-pVQZ and MCSCF/aug-cc-pVQZ levels of theory. This was also the first work where the MB-representation was used for describing DMSs of an XY3 molecule, formulated as follows ... 

The atomic unit (AU) of dipole moment is that of a proton and electron separated by a distance equal to the first Bohr orbit, oq. Similarly, the au of polarizability is Oq [125]. Express and o for NH3 using both the cgs/esu and SI approach. 

In H2O and NH3, shown in Figures 4.18(a) and 4.18(b), the direction of the dipole moment is along the C2 or C3 axis, respectively. In both molecules there are lone pairs of electrons directed away from the 0-FI or N-FI bonds so that the negative end of the dipole is as shown in each case. 

The dipole moment vector /i must be totally symmetric, and therefore symmetric to all operations of the point group to which the molecule belongs otherwise the direction of the dipole moment could be reversed by carrying out a symmetry operation, and this clearly cannot happen. The vector /i has components fiy and along the cartesian axes of the molecule. In the examples of NH3 and NF3, shown in Figures 4.18(b) and 4.18(e), respectively, if the C3 axis is the z-axis, 7 0 but = 0. Similarly in H2O and cis-... 

This dispersion interaction must be added to the dipole-dipole interactions between molecules, such as HCl, NH3 and H2O which have a permanent dipole, fi. The magnitude of die dipole moment depends on tire differences in electronegativity of the atoms in the molecule. Here again, the energy of interaction varies as (orientation effect). 

NF3 is a colourless, odourless, thermodynamically stable gas (mp —206.8°, bp —129.0°, AG29g — 83.3kJmol ). The molecule is pyramidal with an F-N-F angle of 102.5°, but the dipole moment (0.234 D) is only one-sixth of that of NH3 (1.47 D) presumably because the N-F bond moments act in the opposite direction to that of the lone-pair moment ... 

The question arises whether an external electric field will have any large influence on the direction of these proton transfers. In the NH3 molecule all three protons are situated in one hemisphere of the electronic cloud, and so give to the molecule a dipole moment. In the (NH4)+ ion, on the other hand, it is generally accepted that the four protons are placed symmetrically at the corners of a tetrahedron. Accordingly, the (NH4)+ ion will have no dipole moment. 

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... 

Amino acid zwitterions are internal salts and therefore have many of the physical properties associated with salts. They have large dipole moments, are soluble in water but insoluble in hydrocarbons, and are crystalline substances with relatively high melting points. In addition, amino acids are amphiprotic they can react either as acids or as bases, depending on the circumstances. In aqueous acid solution, an amino acid zwitterion is a base that accepts a proton to yield a cation in aqueous base solution, the zwitterion is an add that loses a proton to form an anion. Note that it is the carboxylate, -C02-, that acts as the basic site and accepts a proton in acid solution, and it is the ammonium cation, -NH3+, that acts as the acidic site and donates a proton in base solution. 

If the four atoms attached to the central atom in a tetrahedral molecule are the same, as in tetrachloromethane (carbon tetrachloride), CCI4 (30), the dipole moments cancel and the molecule is nonpolar. However, if one or more of the atoms are replaced by different atoms, as in trichloromethane (chloroform), Cl ICI, or by lone pairs, as in NH3, then the dipole moments associated with the bonds are not all the same, so they do not cancel. Thus, the CHCI, molecule is polar (31). 

Ammonia is a pungent, toxic gas that condenses to a colorless liquid at — 33°C. The liquid resembles water in its physical properties, including its ability to act as a solvent for a wide range of substances. Because the dipole moment of the NH3 molecule (1.47 D) is lower than that of the H20 molecule (1.85 D), salts with strong ionic character, such as KCI, cannot dissolve in ammonia. Salts with polarizable anions tend to be more soluble in ammonia than are salts with greater ionic character. For example, iodides are more soluble than chlorides in ammonia. Liquid ammonia undergoes much less autoprotolysis than water ... 

Both water and ammonia have four groups attached to their central atom and therefore both possess a tetrahedral electronic (or VSF PR) geometry. However, H20 has two unshared electron pairs while NH3 only has one, producing a larger dipole moment for H,0. 

In the "scissors mode" of H2O, the protons move parallel to the surface and the oscillation frequency is almost unaffected. For NH3, on the other hand, the so called "umbrella mode" is drastically stiffened by the surface because the protons move against the surface and suffer a strong Coulomb repulsion. Here again the dynamical dipole moment is dp/da = 2 Pj, slnda. For NHj, where Pjj = 0.53 a.u., the enhancement of the aynamlc dipole by the surface is compensated by the smaller oscillation amplitude. 

Generally the magnitudes of solvent exchange rate constants increase in the sequence NH3 > H20 > DMF > MeCN > MeOH, which is largely independent of the nature of the metal ion (108,109). This sequence cannot be readily identified with specific characteristics such as dielectric constant, donor number, electric dipole moment, or stereochemistry, and it appears to reflect the overall solvent characteristic. There may be a correlation between the AH for solvent exchange on [M(solvent)6]2+ and the heat of dissociation of solvent from this species (110). 

Table 2 Calculated dipole moments [D] of the dihalogens C1F, BrF, BrCl, and NH3 as obtained with different methods applying the aug-cc-pVTZ basis set [36] ...

Figure 2.9 The dipole moment of NH3 is much larger than that of NF3 because a large atomic dipole adds to the vector sum of the NH bond dipoles, whereas a large atomic dipole opposes the vector sum of the large NF atomic dipoles.

One of the interesting aspects of dipole moments for molecules is seen when the molecules NH3 and NF3 are considered ... 

The thermodynamic theory for exp-6 mixtures of polar materials is now implemented in the thermochemical code Cheetah.32 We considered first the major polar detonation products H20, NH3, CO, and HF. The optimal exp-6 parameters and dipole moment values for these species were determined by fitting to a variety of available experimental data. We find, for example, that a dipole moment of 2.2 Debye for water reproduces very well all available experiments. Incidentally, this value is in very good agreement with values typically used to model supercritical water.50... 

If one is interested in changes of the solute molecule, or if the structure of the surrounding solvent can be neglected, it may be sufficient to regard the solvent as a homogeneous dielectric medium, as was done in the older continuum theories, and to perform a quantum mechanical calculation on the molecule with a modified Hamiltonian which accounts for the influence of the solvent as has been done by Hylton et al. 18 5>. Similarly Yamabe et al. 186> substituted dipole-moment operators for the solvent in their perturbational treatment of solvent effects on the activation energy in the NH3 + HF reaction. 

H. Lin, J. Zheng, and W. Thiel, Mol. Phys., 2005, 103, 359], and it makes use of dipole moment surfaces calculated ab initio. We apply the theory to NH3 and demonstrate that the theoretical results show good agreement with experimental findings. 

---