Calculated dipole moments

TabU 3-5 Dipole moments calculated for formaldehyde using various basis sets at the experimental geometry,... 

DIPOLE MOMENTS CALCULATED FOR VARIOUS THIAZOLE DERIVATIVES... 

Which one of the dichlorobenzene isomers does not have a dipole moment" Which one has the largest dipole moment" Compare your answers with the dipole moments calculated using the molecular modeling software in Learning By Modeling... 

In the gas phase H2SO4 and D2SO4 adopt the C conformaiion with r(O-H) 97 pm. r(S-OH) 157.4 pm, r(S-O) 142.2 pm the various jnleralamjc and dihedral angles were also determined and the molecular dipole moment calculated to be 2.73... 

Rashin, A. A., L. Young, I. A. Topol, and S. K. Burt. 1994. Molecular dipole moments calculated with density functional theory. Chem. Phys. Lett. 230, 182. 

The dipole moment calculated for 111 is somewhat higher than for 96, as expected. The total it charge in the cyclopentadiene ring is calculated to be 0.54 electrons. A somewhat smaller polarization, 0.40 tt electrons, is calculated for 7,8-diphenylcalicene (124), and 0.34 tt electrons for hexaphenylcalicene 115, (122) by the PPP (Pariser-Parr-Pople) method. Thus it seems as if the tt polarization roughly follows the same trend as the bond lengths and the C=C torsional barriers. 

The deformed-chair conformation of ring A in a 4,4-dimethyl-3-oxo-5or-steroid has been confirmed by an X-ray study of a 17 -benzoyloxyandrostane derivative. The results agree with those of an earlier study of the 17-iodoacetate, and with the geometry indicated by force-field calculations. Dipole moments calculated by the application of molecular mechanics to 5a-androstane-3,17-dione and its distorted 4,4-dimethyl derivative are larger than those observed the reasons for these deviations are not yet clear. 

None of the semi-empirical models are as successful. Mean absolute errors are two to three times larger than for other models, and individual molecules often show errors larger than the dipole moments themselves. In addition, a number of subtle effects are not properly reproduced. Overall, semi-empirical models do not offer a good choice for dipole moment calculations in hydrocarbons (and presumably as well in other molecules of low polarity). 

Tables 12-23 to 12-26 examine the effect of geometry on dipole moments in a small collection of hydrocarbons and amines. Singlepoint 6-31G, EDF1/6-31G, B3LYP/6-31G and MP2/6-31G dipole moment calculations have been carried out using MMFF, AMI and (except for the Hartree-Fock calculations) 6-3IG geometries, and compared with dipole moments obtained from exact structures. While subtle differences exist, for the most part they are very small. In fact, using mean absolute error as a criterion, there is little to differentiate dipole moments obtained from use of approximate geometries from those calculated using exact geometries.

Dielectric constants are determined for pure liquid dimethylsiloxane oligomers. Mean-square dipole moments, calculated from the Onsager equation, are in good agreement with predicted values based on the RIS model (S 117) with neighbor dependence and chain conformational energies obtained in an independent analysis of the random-coil dimensions of such chains. In addition, the observed temperature coefficients of are in qualitative agreement with calculated results. 

Dipole moments calculated by the method of Mazeika et al.252 for derivatives of 1 and 5 are summarized in Table II. The results compare with experimental values of 1.5 and 3.4 D for 1- and 2-methylindazole.253... 

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