Molecular properties nuclear magnetic moment

As a final example of molecular properties, consider the molecular electronic system in the presence of a static external magnetic induction B and nuclear magnetic moments M/c, corresponding to the physical situation encountered in an NMR experiment. Expanding the energy of a closed-shell electronic system in the induction and in the nuclear magnetic moments, we obtain... 

In the first, quantum mechanics can be used to calculate the NMR coupling constant between two nuclear spins in the molecular environment or the NMR shielding constant. Jensen [8] in Chapter 10 of the reference provides a comprehensive introduction to the methods for calculating these molecular properties. The NMR coupling constant, KAB, is related to the second derivative of the energy with respect to the internal magnetic moments, /u, arising from the nuclear spin of the two atoms, A and B. 

In the literature, one finds a bimodal distribution of parameter quality. On the one hand is the force field developer who makes monumental efforts to minimize the error between computed and experimental molecular properties. Parametarizations often involve fits to physical data such as molecular structure (bond lengths and bond angles), vibrational data, and heats of formation. Sometimes fittings also include molecular dipole moments, heats of sublimation, or rotational barriers from nuclear magnetic resonance or other spectroscopic measurements. Well-tested, high quality parameters are the result. Some of the better force fields were compared by Pettersson and Liljefors in Volume 9 of this series. ... 

It can now be predicted with confidence that machine calculations will lead gradually toward a really fundamental quantitative understanding of the rules of valence and the exceptions to these toward a real understanding of the dimensions and detailed structures, force constants, dipole moments, ionization potentitils, and other properties of stable molecules and equally unstable radicals, anions, and cations, and chemical reaction intermediates toward a basic understanding of activated states in chemical reactions, and of triplet and other excited states which are important in combustion and explosion processes and in photochemistry and in radiation chemistry and also of intermolecular forces further, of the structure and stability of metals and other solids of those parts of molecular wave functions which are important in nuclear magnetic resonance, nuclear quadrupole coupling, and other interaction involving electrons and nuclei and of very many other aspects of the structure of matter which are now understood only qualitatively or semi-empirically. 

The Born-Oppenheimer approximation [96], created to simpUfy the electronic calculus for frozen nuclei approximation, breaks down when computing, for instance, the magnetic dipole moment and its derivative with respect to the nuclear velocities or momenta for assessing the molecular properties of surfaces [97]. 

Closely related to the PES is the concept of property surfaces (PSs). Molecular properties such as the dipole moment, polarizability, and NMR shielding depend on the response ofthe wave function to applied electric and/or magnetic fields and their values as functions ofthe nuclear coordinates define the various PSs. Both the potential energy and the PSs are strongly related to spectroscopic properties,... 

With the gauge origin at the nucleus in question, o in Ramsey s expression is related to another molecular property, the nuclear spin-rotation constant. The nuclear spin-rotation constant arises from the coupling of the magnetic moment of a nucleus with the magnetic field generated by the molecular rotation at that nucleus. Ramsey and Flygare have shown that... 

Traditional physical and physico-chemical methods paesent information about various macroscopic (bulk) parameters such as viscosity, q, dielectric constants 8, dipale moments p, refractive indices no, and some others at different temperatures. Several experimental methods are used for recording molecular dynamic properties in liquid solutions nuclear magnetic resonance spectroscopy (NMR), fluorescence, ionic conductivity, electron paramagnetic resonance (EPR) spectroscopy, and some others. However, such processes as salvation, chemical interaction between reagents, electron and energy transfer, etc., take... 

To a physical organic chemist, dipole moment and molecular refraction are electronic properties par excellence—so is optical activity, which is determined, as it were, by the topology of the motion of charge through the molecule under the influence of the electric component of a radiation field so also are the chemical shift of the frequency of nuclear magnetic resonance and the nuclear qvadrupoU coupling constant, both of which serve as sensitive probes into the electronic environment of the nucleus. 

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