Ultraviolet-visible molecular

GC, gas chromatography HPLC, high-performance liquid chromatography MS, mass spectroscopy AA, atomic absorption GFAA, graphite furnace atomic absorption ICP, inductively coupled plasma UV-VIS, ultraviolet-visible molecular absorption spectroscopy IC, ion chromatography. 

Ouantitative IR absorption methods differ somewhat from ultraviolet-visible molecular spectroscopic methods because of the greater complexity of the spectra, the narrowness of the absorption bands, and ilie instrumental limitations of IR instruments. (Quantitative data obtained with older dispersive IR instruments were generally signilicantly inferior in quality to data obtained with UV visible speclrophotomelers. 1 he precision and acciir icyof measurements with modern F TIR iustrumenis, however, is distinctiv betler than those... 

Ultraviolet-visible molecular absorption spectrometers This type of instrument owes much of its popularity to the availability of a large number of... 

Ultraviolet visible (UV VIS) spectroscopy, which probes the electron distribution especially m molecules that have conjugated n electron systems Mass spectrometry (MS), which gives the molecular weight and formula both of the molecule itself and various structural units within it... 

Ultraviolet-visible spectroscopy (UV = 200 - 400 nm, visible = 400 - 800 nm) corresponds to electronic excitations between the energy levels that correspond to the molecular orbital of the systems. In particular, transitions involving n orbital and ion pairs (n = non-bonding) are important and so UV/VIS spectroscopy is of most use for identifying conjugated systems which tend to have stronger absorptions... 

A fluorescent species is termed a fluorophore or fluor analogous to a chromophore in ultraviolet-visible (UV-vis) specttoscopy. Eluorophores are native chemical species or moieties that exhibit emission upon excitation, often by incident light of the proper wavelength and intensity. Molecular snuctural analysis serves... 

Molecular absorption spectroscopy deals with measurement of the ultraviolet-visible spectrum of electromagnetic radiation transmitted or reflected by a sample as a function of the wavelength. Ordinarily, the intensity of the energy transmitted is compared to that transmitted by some other system that serves as a standard. 

Spectroscopy produces spectra which arise as a result of interaction of electromagnetic radiation with matter. The type of interaction (electronic or nuclear transition, molecular vibration or electron loss) depends upon the wavelength of the radiation (Tab. 7.1). The most widely applied techniques are infrared (IR), Mossbauer, ultraviolet-visible (UV-Vis), and in recent years, various forms ofX-ray absorption fine structure (XAFS) spectroscopy which probe the local structure of the elements. Less widely used techniques are Raman spectroscopy. X-ray photoelectron spectroscopy (XPS), secondary ion imaging mass spectroscopy (SIMS), Auger electron spectroscopy (AES), electron spin resonance (ESR) and nuclear magnetic resonance (NMR) spectroscopy. 

Zerner s intermediate neglect of differential overlap (ZINDO)/PM3 calculations of thiazinylium compound 35 were compared to its ultraviolet/visible (UVA is) absorption spectrum (Figure 3) <2000JOC6388>. The authors attribute the observed 453 and 403 nm bands (calculated to be at 456 and 412 nm) to highest occupied molecular orbital (HOMO)-LUMO and HOMO-LUMO + 1 transitions of the 1,2-thiazine sulfonium imide. 

Like diffraction, spectroscopic methods using ultraviolet, visible, or infrared light are generally much Easier than molecular vibrations or interconversions, and the... 

Spectrophotometric Techniques Based on Molecular Absorption Radiation Ultraviolet-Visible Spectrophotometry... 

Molecular dynamics (MD) simulations fill a significant niche in the study of chemical structure. While nuclear magnetic resonance (NMR) yields the structure of a molecule in atomic detail, this structure is the time-averaged composite of several conformations. Electronic and vibrational circular dichroism spectroscopy and more general ultraviolet/visible and infrared (IR) spectroscopy yield the secondary structure of the molecule, but at low resolution. MD simulations, on the other hand, yield a large set of individual structures in high detail and can describe the dynamic properties of these structures in solution. Movement and energy details of individual atoms can then be easily obtained from these studies. 

In addition to IR and NMR spectroscopy there are many other instrumental techniques that are useful to the organic chemist. Two of these, ultraviolet-visible spectroscopy and mass spectrometry, are discussed in this chapter. Ultraviolet-visible spectroscopy is presented first. The use of this technique to obtain information about the conjugated part of a molecule is described. Then mass spectrometry is discussed. This technique provides the molecular mass and formula for a compound. In addition, the use of the mass spectrum to provide structural information about the compound under investigation is presented. 

MOLECULAR SPECTROSCOPY 4.35.3.1 Ultraviolet-Visible Absorption Spectroscopy... 

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