Electrostatic potential dipole

Improvements of the Pohtzer hydrophobic model were later proposed using additional quantum-chemical descriptors derived from the molecular electrostatic potential, dipole moment, and ionization energies. These descriptors were searched for to give the best estimations of the cavity term, polarity/dipolarizability term, and hydrogen-bond parameters defined in -> linear solvation energy relationships [Haeberlein and Brinck, 1997]. 

Improvements of the Politzer hydrophobic model were later proposed using additional —> quantum-chemical descriptors derived from the molecular electrostatic potential, dipole moment. 

Many molecular properties can be related directly to the wave function or total electron density. Some examples are dipole moments, polarizability, the electrostatic potential, and charges on atoms. 

Examine the molecular models of H2 HE CH4 CH3F and CF4 Find the calculated dipole moment of each compound and examine their electrostatic potential maps... 

Examine the molecular model of ferrocene on Learning By Modeling Does ferrocene have a dipole moment Would you expect the cyclopentadienyl nngs of ferrocene to be more reactive toward nucleophiles or electrophiles Where is the region of highest electrostatic potential... 

Find the molecular model of 18 crown 6 (see Figure 16 2) on Learning By Modeling and examine its electrostatic potential map View the map in vanous modes (dots contours and as a transparent surface) Does 18 crown 6 have a dipole moment Are vicinal oxygens anti or gauche to one another"d... 

In addition to total energy and gradient, HyperChem can use quantum mechanical methods to calculate several other properties. The properties include the dipole moment, total electron density, total spin density, electrostatic potential, heats of formation, orbital energy levels, vibrational normal modes and frequencies, infrared spectrum intensities, and ultraviolet-visible spectrum frequencies and intensities. The HyperChem log file includes energy, gradient, and dipole values, while HIN files store atomic charge values. 

Energy, geometry, dipole moment, and the electrostatic potential all have a clear relation to experimental values. Calculated atomic charges are a different matter. There are various ways to define atomic charges. HyperChem uses Mulliken atomic charges, which are commonly used in Molecular Orbital theory. These quantities have only an approximate relation to experiment their values are sensitive to the basis set and to the method of calculation. 

The orientational structure of water near a metal surface has obvious consequences for the electrostatic potential across an interface, since any orientational anisotropy creates an electric field that interacts with the metal electrons. Hydrogen bonds are formed mainly within the adsorbate layer but also between the adsorbate and the second layer. Fig. 3 already shows quite clearly that the requirements of hydrogen bond maximization and minimization of interfacial dipoles lead to preferentially planar orientations. On the metal surface, this behavior is modified because of the anisotropy of the water/metal interactions which favors adsorption with the oxygen end towards the metal phase. 

Decide if ion-dipole interactions are responsible for the observed substituent effects. Obtain the charge on carbon and nitrogen in each cyano group. What evidence is there for a polar CN bond Should the ion (O )-dipole (CN) interaction be stabilizing or destabilizing Can these interactions explain the trends in electrostatic potential (Hint Focus on changes in O—CN distance and in orientation of the cyano group.)... 

Examine electrostatic potential maps for potassium hydride and hydrogen chloride. How are they similar and how are they different (Focus on whether the molecules are polar or nonpolar (compare dipole moments), and on the electronic character of hydrogen.) Draw the ionic Lewis structure that is most consistent with each electrostatic potential map. Does each atom have a filled valence shell ... 

Repeat your analysis for tautomeric equilibria between 4-hydroxypyridine and 4-pyridone, 2-hydroxypyrimidine and 2-pyrimidone and 4-hydroxypyrimidine and 4-pyrimidone. For each, identify the favored (lower-energy) tautomer, and then use equation (1) to calculate the ratio of tautomers present at equilibrium. Point out any major differences among the four systems and rationalize what you observe. (Hint Compare dipole moments and electrostatic potential maps of the two pyridones and the two pyrimidones. How are these related to molecular stability )... 

Compare the dipole moment and the electrostatic potential map for the ground state of acetone to those of the n to pistar state of acetone. Which molecule is more polar Rationalize the differences by appealing to the shape of the orbitals (in ground-state acetone) whose electron populations are changed by excitation. 

Many physical properties such as the electrostatic potential, the dipole moment and so on, do not depend on electron spin and so we can ask a slightly different question what is the chance that we will find the electron in a certain region of space dr irrespective of spin To find the answer, we integrate over the spin variable, and to use the example 5.2 above... 

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