Structural analyses dipole moment

The remainder of the optimization output file displays the population analysis, molecular orbitals (if requested with Pop=Reg) and atomic charges and dipole moment for the optimized structure. 

The foregoing conclusions are further supported by a refined X-ray analysis of pyrid-2-one, which indicated that the mobile hydrogen atom is attached to the nitrogen atom in the solid state and that individual molecules are bound into helices by N—H- -0 hydrogen bonds. An oxo structure is also indicated by the molar refractivity of pyrid-2-one. The dipole moment of 4-methoxypyridine is ca. 3.0 debyes in dioxane, whereas the values for pyrid-4-one and its 1-methyl derivative are much higher, ca. 6.0 debyes indicating the... 

Dipole moments of azolides have been reviewed, with emphasis on the conformation of the acyl group. 441 Unfortunately, structural and conformational studies on azolides by X-ray structure analysis are almost totally lacking, although they would be of great interest with regard to the conformations and to the bond lengths and bond orders in these systems. Only an X-ray analysis of V-acetyl-4-bromopyrazole 451 has been reported. 

Of special interest (see Table II) is the structure of compound XVI, obtained in a reaction with thermodynamic control, and its sulfide (XVII), as both molecules contain the P—H bond. Infrared, Raman, and NMR studies as well as dipole moment measurements showed that the P—H bond was axial in these compounds. In some cases the conclusions of NMR and dipole moment studies were verified by X-ray single-crystal analysis. 

In Section 4.2 an analysis based on bond lengths and dipole moments was presented showing that structures I and II contribute about equally to the actual structure. Nitrous oxide functions as an oxidizing agent that can react explosively with H2,... 

Relative contribution of each of these structures differs significantly and is determined by internal structural characteristics of the nitrones and by the influence of external factors, such as changes in polarity of solvent, formation of a hydrogen bond, and complexation and protonation. Changes in the electronic stmcture of nitrones, effected by any of these factors, which are manifested in the changes of physicochemical properties and spectral characteristics, can be explained, qualitatively, by analyzing the relative contribution of A-G structures. On the basis of a vector analysis of dipole moments of two series of nitrones (355), a quantum-chemical computation of ab initio molecular orbitals of the model nitrone CH2=N(H)0 and its tautomers, and methyl derivatives (356), it has been established that the bond in nitrones between C and N atoms is almost... 

The microwave spectrum of SeOF2 served for an extended analysis of the structure of this molecule. The following parameters have been deduced rSeo = 1.576 rScK = 1.7295 A FSeF = 92.22° OSeF = 104.82°. The dipole moment is 2.84 D along an axis at an angle of 50.30° to the SeO bond and in the plane that contains this bond and bisects the FSeF angle (22). 

Two permanent merocyanines have been reported for the spiro-oxazines [85]. These were NOSH heteroanellated by imidazo [l,2-a]pyridine and imidazo [l,2-a]pyrimadine. Several tests have been conducted to determine the nature of these species. H -NMR data show that the indoline nitrogen is not highly charged and the crystal structure indicates that the ground state is essentially the quinoidal form. The most stable form was found to be the TTC isomeric form by x-ray analysis. The dipole moment of these permanent spiro-oxazine merocyanines was around 3.84 D, which is much lower than the values reported for spiropyran merocyanines. 

Alkylation of 5-phenylrhodanines (122) with alkyl iodides and sodium ethoxide yields the meso-ionic 2-alkylthio-l,3-thiazol-4-ones (114, R = SR) 78a structure of the compound 114, R = SMe, R = NHj, R = Ph, was established by X-ray analysis. The dipole moment of the compound 114, R = R = Me, R = Ph, in benzene solution is 5.21 D. Irradiation of the meso-ionic l,3-thiazole-4-thione (114, R = SMe, R = Me, R = Ph) in ethanol yields the isomeric 3-methyl-4-methylthio-5-phenyl-l,3-thiazol-2-one. A novel mechanism for this photochemical rearrangement has been proposed. ... 

The N-alkylcarboxamides, originally synthesized for potential cooling activity, were analyzed by molecular modeling (29) (J. Brahms, unpublished studies). The analysis used calculated electronic and steric stmcturd properties, i.e. molecular volume, dipole moment, and logP, to correlate the reported oral threshold values with chemical structure resulting in a predictive model [FIGURE 6]. The thresholds of the carboxamide coolants were consistent with this model. 

The electronic structure of fluorenes and the development of their linear and nonlinear optical structure-property relationships have been the subject of intense investigation [20-22,25,30,31]. Important parameters that determine optical properties of the molecules are the magnitude and alignment of the electronic transition dipole moments [30,31]. These parameters can be obtained from ESA and absorption anisotropy spectra [32,33] using the same pump-probe laser techniques described above (see Fig. 9). A comprehensive theoretical analysis of a two beam (piunp and probe) laser experiment was performed [34], where a general case of induced saturated absorption anisotropy was considered. From this work, measurement of the absorption anisotropy of molecules in an isotropic ensemble facilitates the determination of the angle between the So Si (pump) and Si S (probe) transitions. The excited state absorption anisotropy, rabs> is expressed as [13] ... 

Measurements of dipole moments, Kerr constants, and dielectric absorption have been employed (81RCR336) widely to obtain information on the conformational equilibrium in acyl heterocycles. Details on conformer structures and populations depend on the choice of additive scheme, group moments, or polarizability tensor in the case of Kerr constants. Several early conclusions, especially for furan- and thiophene-2-carboxaldehyde, appeared contradictory, owing to the choice of these quantities. A more precise definition of polarizability tensors for several heterocycles and a choice of group moments and additive schemes tested on a large amount of available experimental results and supported by accurate theoretical calculations have led to more confidence in the use of experimental dipole moments and Kerr constants in conformational analysis. A limitation of the method is that the... 

For the description of a solution of alanine in water two models were compared and combined with one another (79), namely the continuum model approach and the cluster ansatz approach (148,149). In the cluster approach snapshots along a trajectory are harvested and subsequent quantum chemical analysis is carried out. In order to learn more about the structure and the effects of the solvent shell, the molecular dipole moments were computed. To harvest a trajectory and for comparison AIMD (here CPMD) simulations were carried out (79). The calculations contained one alanine molecule dissolved in 60 water molecules. The average dipole moments for alanine and water were derived by means of maximally localized Wannier functions (MLWF) (67-72). For the water molecules different solvent shells were selected according to the three radial pair distributions between water and the functional groups. An overview about the findings is given in Tables II and III. 

Drug binding is enhanced by hydrophobicity in that portion of the drug that binds to the pocket toe. Quantitative structure-activity relationship (QSAR) analysis of these compounds have consistently shown that the most predictive parameter of antiviral activity is a measure of hydrophobicity, the octanol water partition coefficient (logP) [80,82,85]. These studies have also consistently shown that there is no apparent correlation between electrostatic potential or dipole moment and potency. 

A RIS model with neighbor interactions is used to calculate mean-square unperturbed dimensions and dipole moments for vinyl chloride chains having degrees of polymerization ranging from x = 1 to 1 50 and stereochemical structures ranging from perfect syndiotacticity to perfect isotacticity. Conformational energies used in these calculations are those which have been established in the analysis based on the stereochemical equilibration of 2,4-dichloro-n-pentane by Flory and Williams (A 002). 

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