Ketones ultraviolet spectroscopy

The use of trifluoroethanol as solvent or absorption of the dienone on silica gel promotes the photoconversion of dienones into bicyclic ketenes.<47) For the photolysis<48 60) of (63) it has been shown by low-temperature infrared and ultraviolet spectroscopy that the initial photolysis gives a ketene which can be efficiently trapped by cyclohexylamine or, in the absence of a good nucleophile, thermally rearranges by a OA, + 20) allowed process to a bicyclic ketone (64) ... 

The photo-Fries reaction occurs readily in solid polymers and is observable in phenyl esters, particularly in poly(phenyl acrylate) and poly (phenyl methacrylate) and their derivatives. The course of the reaction can be followed very easily by ultraviolet spectroscopy, since the product hydroxy ketones have strong absorbance at 260 and 320 nm (Fig. 10). Reaction occurs with equal efficiency in small model compounds in solution and in the polymers in the solid phase (44). An Arrhenius plot of the quantum yield for the para product (Fig. 11) shows a linear increase up to 294 K, above which no further change in quantum efficiency is observed, either above or below the glass transition temperature. 

Morisawa, Y., Ikehata, A., Higashi, N., Ozaki, Y. Low-n Rydbeig transitions of liquid ketones studied by attenuated total reflection far-ultraviolet spectroscopy. J. Phys. Chem. A 115, 562-568 (2011)... 

The concentrations of the different intermediates are determined by the equilibrium constants. The observation of immonium ions [Eq. (5)] in strongly acidic solutions by ultraviolet and NMR spectroscopy also Indicates that these equilibria really exist (23,26). The equilibria in aqueous solutions are of synthetic interest and explain the convenient method for the preparation of 2-deuterated ketones and aldehydes by hydrolysis of enamines in heavy water (27). 

If a soluble reagent containing an ultraviolet (UV)-active group or dye can be used, then it may be possible to estimate the reaction yield from the amount of unreacted reagent stiU remaining in the supernatant solution at the end of the reaction. For example, the derivatization of aldehydes and ahphatic ketones with dansylhydrazine has been monitored by fluorescence spectroscopy of the supernatant solution, and has been used to quantify the amount of supported aldehyde or ketone. 

Bernstein et al. have used IR spectroscopy and mass spectrometry to study the products formed from photochemical transformation of naphthalene, anthracene, chrysene, phenanthrene, pyrene, tetracene, pentacene, perylene, benzo(e)pyrene, benzo(ghi)perylene, and coronene in water ices using ultraviolet radiation under astrophysical conditions [27]. The results of their investigation have revealed that peripheral carbon atoms can be oxidized to produce aromatic alcohols, ketones, ethers (when bay region is present,... 

A solvent for ultraviolet/visible spectroscopy must be transparent in the region of the spectrum where the solute absorbs and should dissolve a sufficient quantity of the sample to give a well-defined analyte spectrum. In addition, we must consider possible interactions of the solvent with the absorbing species. For example, polar solvents, such as water, alcohols, esters, and ketones, tend to obliterate vibration spectra and should thus be avoided to preserve spectral detail. Nonpolar solvents, such as cyclohexane, often provide spectra that more closely approach that of a gas (compare, for example, the three spectra in Figure 24-14). In addition, the polarity of the solvent often influences the position of absorption maxima. For qualitative analysis, it is therefore important to compare analyte spectra with spectra of known compounds measured in the same solvent. 

In the examination of plant waxes various analytical methods have been used, including ultraviolet and infrared spectroscopy, and thin-layer, column, and gas-liquid chromatographies (Eglinton and Hamilton, 1967). The infrared spectrum has been used to indicate hydroxy compounds, ketones, ethers, and lactones, as well as the more common esters and hydrocarbons. In the use of thin-layer or column chromatography, infrared spectra can be used to make sure that there is no carryover of one class of components into another. 

The application of ultraviolet (UV) spectroscopy in the elucidation of the structure of terpenes and other natural products was extensively used by R.B. Woodward in the early forties of the last century. On the basis of his large collection of empirical data, he developed a series of rules (later called the Woodward rules), which could be applied to nding out the structures of new natural substances by correlations between the position of UV maximum absorption and the substitution pattern of a diene or an a,p-unsaturated ketone (Woodward, 1941). He was awarded the Nobel Prize in Chemistry in 1965. However, it was not until the introduction of chromatographic separation methods and nuclear magnetic resonance (NMI spectroscopy into organic chemistry that a lot of further structures of terpenes were elucidated. The almost exponential growth in our knowledge in that eld and other essential oil constituents is essentially due to the considerable advances in analytical methods in the course of the last half century. 

---