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In organic chemistry, umpolung (German: [ˈʔʊmˌpoːlʊŋ]) or polarity inversion is the chemical modification of a functional group with the aim of the reversal of polarity of that group. [ 1 ] [ 2 ] This modification allows secondary reactions of this functional group that would otherwise not be possible. [ 3 ]
Yet, before the experiments of Stanciu and Hansteen, all-optical controllable magnetization reversal in a stable magnetic state was considered impossible. [ 1 ] In quantum field theory and quantum chemistry the effect where the angular momentum associated to the circular motion of the photons induces an angular momentum in the electrons is ...
The Earth's magnetic field is approximately four times stronger today than it was during the Gauss–Matuyama reversal. [4] The reversal is thought to have weakened the shielding that the magnetic field provides the surface Earth, resulting in more exposure to ionizing radiation generated by the early Pleistocene supernova , and leaving the ...
Reversal of the solar magnetic field; Magnetization reversal, a process leading to a 180° reorientation of the magnetization vector with respect to its initial direction; Polarity reversal (seismology), a local amplitude seismic anomaly
The Earth's magnetic field has alternated between periods of normal polarity, in which the predominant direction of the field was the same as the present direction, and reverse polarity, in which it was the opposite. These periods are called chrons. Reversal occurrences are statistically random.
Magnetochemistry is concerned with the magnetic properties of chemical compounds and elements. Magnetic properties arise from the spin and orbital angular momentum of the electrons contained in a compound. Compounds are diamagnetic when they contain no unpaired electrons. Molecular compounds that contain one or more unpaired electrons are ...
Magnetic polarizability likewise refers to the tendency for a magnetic dipole moment to appear in proportion to an external magnetic field. Electric and magnetic polarizabilities determine the dynamical response of a bound system (such as a molecule or crystal) to external fields, and provide insight into a molecule's internal structure. [2] "
In the magnetic pole model, the magnetic dipole moment is due to two equal and opposite magnetic charges that are separated by a distance, d. In this model, m is similar to the electric dipole moment p due to electrical charges: m = q m d , {\displaystyle m=q_{\mathrm {m} }d,} where q m is the ‘magnetic charge’.