Visible and UV absorption

Another example is provided by [30] anmlene. Longuet-Higgins and Salem have shown that the observed visible and UV absorption spectrum and, in particular, the NMR proton chemical shifts of this molecule are very difficult to reconcile with the symmetrical nuclear configuration (Dg ) suggested by the superposition of the Kekule-type resonance structures. The hypothesis of a bond-length alternation of symmetry removes this difficulty. This indicates that the resonance between Kekule-type structures should be very much impeded also in this molecule. 

Figure 1. Visible and UV absorption spectra obtained from an alcoholic solution...

Routine quantitative analysis, enzyme analysis and kinetics. More sensitive at lower concentrations than visible and UV absorption. 

Atoms, neutral molecules, and ions (simple and assoeiated) ean exist in several possible electronic states this is the basis of visible and UV absorption spectroscopy. Transitions between these energy states occur by the absorption of discrete energy quanta A which are related to the frequency v of the light absorbed by the well-known relation... 

The method of visible and UV absorption spectroscopy is at its best when the absorption spectra of the free ions and the associated ions are quite different and known. When the associated ions cannot be chemically isolated and their spectra studied, the type of absorption by the associated ions has to be attributed to electronic transitions known from other well-studied systems. For example, there can be an electron transfer to the ion from its immediate environment (charge-transfer spectra), i.e., from the entities associated with the ion or transitions between new electronic levels produced in the ion under the influence of the electrostatic field of the species associated with the ion (crystal-field splitting). Thus, there is an influence of the environment on the absorption characteristics of a species, and this influence reduces the clarity with which spectra are characteristic of species rather than of their environment. Herein lies what may be considered a disadvantage of visible and UV absorption spectroscopy. 

Visible and UV absorption spectroscopy are based on studying that part of the incident light transmitted (after absorption) through an electrolytic solution in the same direction as the original beam. However, a certain amount of light is scattered in other directions. 

CD of Rhodiumd) Complexes. Figure 2 shows the visible and UV absorption of r 2-olefin complexes of rhodiumd). The synthesis of these complexes has been reported elsewhere. (S) It is seen that r 2-olefins give absorption peaks or shoulders in the regions... 

Detailed UV spectroscopic studies on the deep colored dimers (34) and related compounds have been published. The visible and UV absorptions of derivatives with various ethylene chains have been compared <86KGS1693,88KGS418>. 

Visible and ultraviolet spectra The use of visible and UV absorption and fluorescent spectral characteristics to detect juice adulteration has also been developed, with the presence or absence of specific absorption maxima at selected wavelengths indicating adulteration. 

WAVENUMBERS (y, 10 cm ) OF VISIBLE AND UV ABSORPTION BANDS OF IR0N(1I) AND IRON(III) DIIMINE COMPLEXES,... 

Most modern scanning densitometers allow in situ measurement of visible and UV absorption and fluorescence excitation and omission spectra. As is true ftn IR spectra, sample and standard spectra from the same plate must be directly compared. A lack of a match between in situ sample and standard spectra is definite proof that the compounds in the zone are different, but an apparent match may not be sufficient proof that the compounds are the same if the spectra are not characteristic of the total molecular structure (29). If the corresponding standards are not available for comparison to presumptive sample zones, UV-vis and fluorescence spectra are usually not sufficiently characteristic to identify unknowns by making structural assignments through spectral interpretation. Recording UV-vis spectra of separated zones both before and after postchromatographic derivitization increases the probability of correct zone identification (48). 

The transitions which are responsible for visible and UV absorption by complexes may be classified as follows. 

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