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Absorption spectrum of an aqueous solution of potassium permanganate, showing a vibronic fine structure in the LMCT band. The tetraoxides of d 0 metal centers are often deeply colored for the first row metals. This coloration is assigned to LMCT, involving transfer of nonbonding electrons on the oxo ligands to empty d-levels on the metal.
For example, the d-d transitions for [Cr(NH 3) 5 Cl] 2+ are weak (ε < 100) even though the complex is only of C 4v symmetry. [5] The Laporte rule helps explain the intense colors often observed for the tetrahedral complexes. The tetrahedral point group lacks the inversion operation, so the Laporte rule does not apply. [6]
This lists the character tables for the more common molecular point groups used in the study of molecular symmetry.These tables are based on the group-theoretical treatment of the symmetry operations present in common molecules, and are useful in molecular spectroscopy and quantum chemistry.
For example, the colour of chromate, dichromate and permanganate ions is due to LMCT transitions. Another example is that mercuric iodide , HgI 2 , is red because of a LMCT transition. A metal-to-ligand charge transfer (MLCT) transition will be most likely when the metal is in a low oxidation state and the ligand is easily reduced.
A well-known example is the complex formed by iodine when combined with starch, which exhibits an intense purple charge-transfer band. This has widespread use as a rough screen for counterfeit currency. Unlike most paper, the paper used in US currency is not sized with starch. Thus, formation of this purple color on application of an iodine ...
The invariance properties of molecular descriptors can be defined as the ability of the algorithm for their calculation to give a descriptor value that is independent of the particular characteristics of the molecular representation, such as atom numbering or labeling, spatial reference frame, molecular conformations, etc. Invariance to molecular numbering or labeling is assumed as a minimal ...
For example, the absorption spectrum for ethane shows a σ → σ* transition at 135 nm and that of water a n → σ* transition at 167 nm with an extinction coefficient of 7,000. Benzene has three aromatic π → π* transitions; two E-bands at 180 and 200 nm and one B-band at 255 nm with extinction coefficients respectively 60,000, 8,000 and 215.
Second law [ edit ] Faraday discovered that when the same amount of electric current is passed through different electrolytes connected in series, the masses of the substances deposited or liberated at the electrodes are directly proportional to their respective chemical equivalent/ equivalent weight ( E ). [ 3 ]