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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 ...
Technologically, this is one of the most important processes in magnetism that is linked to the magnetic data storage process such as used in modern hard disk drives. [5] As it is known today, there are only a few possible ways to reverse the magnetization of a metallic magnet: an applied magnetic field [5]
Polarity inversion may refer to: Polarity inversion (chemistry) (aka Umpolung ), in organic chemistry Polarity inversion (differential pairs) , swapping of positive and negative wires in differential signal links
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 chemistry, polarity is a separation of electric charge leading to a molecule or its chemical groups having an electric dipole moment, with a negatively charged end and a positively charged end. Polar molecules must contain one or more polar bonds due to a difference in electronegativity between the bonded atoms.