Paramagnetism and Diamagnetism

For some solid materials, each atom possesses a permanent dipole moment by virtue of incomplete cancellation of electron spin and/or orbital magnetic moments. In the absence of an external magnetic field, the orientations of these atomic magnetic moments are random, such that a piece of material possesses no net macroscopic mag-paramagnetism netization. These atomic dipoles are free to rotate, and paramagnetism results when 

Both diamagnetic and paramagnetic materials are considered nonmagnetic because they exhibit magnetization only when in the presence of an external field. Also, for both, the flux density B within them is almost the same as it would be in a vacuum. 

Room-Temperature Magnetic Susceptibilities for Diamagnetic and Paramagnetic Materials 

Material Susceptibility X (volume) (SI units) Material Susceptibility X (volume) (SI units) 

A useful property for characterising magnetic materials is the magnetic susceptibility, x, defined as the magnetisation, M, divided by the applied 

H Magnetic field strength. Unit ampere per metre, A/m. A field of 1 A/m is produced by an infinitely long solenoid with n turns per metre of coil, carrying a current of 1/n, A. 

M Magnetisation defined as magnetic moment per volume unit. Unit A/m. (Sl-Sommerfeld.) 

I Intensity of magnetisation same definition, but I = //qM, where Po the permeability of free space, 47t x 10 H/m I therefore has the unit of the Tesla, T, or weber/m (Wb/m ). (SI-Kennelly.) 

B Magnetic induction. Unit T (Wb/m ). A magnetic induction 1 T generates a force of 1 N/m on a conductor carrying a current of 1 A, perpendicular to the direction of induction. 

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The shielding tensor, and its diamagnetic and paramagnetic components, are not necessarily symmetric in the Cartesian indices [25-29], and the shielding tensor can in general be decomposed into a symmetric and an antisymmetric component, i.e. 

As indicated, the possibility of orbital decomposition is retained in the diamagnetic and paramagnetic terms in eqs.(29,30). The value for the paramagnetic shielding contribution extracted via eq.(30) does not, of course, correspond to a well-defined basis set, but is at the same level of numerical quality as the LORG calculation used for the total shielding. 

Supercritical water reactions, 24 16-17 Supercurrents, diamagnetic and paramagnetic, 23 802-803 Superdex, 3 839 Superdislocation, 13 499 Superdispersants, 3 677 Superduplex stainless steels... 

Table II shows that the observed 29) shifts 8 (taken as positive downfield) show a degree of linear additivity in the methyl-substituted methanes, with a shortfall for neopentane. Table II shows also the division of the shielding into atom-plus-ligand diamagnetic and paramagnetic parts, relative to methane for which era is 295 ppm. The diamagnetic terms were calculated by Flygare s method 25). With each substitution of hydrogen by carbon, aa for the central carbon increases by 28 ppm but o-p increases by about 37 ppm, and the line moves 9 ppm downfield. Analogous relationships have been demonstrated for shielding in methyl-substituted NH3 and NH4+ 30). Table II shows that the shortfall at neopentane is in the paramagnetic term.

Another interesting point is to be presented in relation to chemical shift evaluations. From the directly-measured spin-rotation constant of POF3, diamagnetic and paramagnetic contributions to phosphorus chemical shifts were estimated (ca. +1000 and —640 p.p.m.). Extended to H3P04, which is the commonly accepted reference compound, this gives about 320 p.p.m. for the absolute 31P chemical shift.a999,9)... 

Utilize the concepts of molecular orbital and hybridization theories to explain multiple bonds, bond angle, diamagnetism, and paramagnetism. 

Clark and Odell have found (39) that the susceptibility varies with temperature in a way that can be explained very well on the basis of temperature-dependent equilibria between diamagnetic and paramagnetic forms. This is valid equally for pyridine and for inert solvents. Thermodynamic quantities calculated from these measurements show that the paramagnetic forms have the lower enthalpies, and that there are relatively large increases of entropy on going from the paramagnetic to the diamagnetic forms. 

Chemical shifts, as treated by Ramsey (113), are comprised of separate diamagnetic and paramagnetic contributions. The diamagnetic term was considered to arise from the response of the extranuclear electrons to the external magnetic field and had been given earlier by Lamb (65) as... 

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