Aromatic hydrocarbon absorption

TABLE 6.5 Absorption Spectra of Aromatic Hydrocarbons—Absorption Maxima of Highest Wavelength... 

Burdett, R.A., L.W. Taylor and L.C. Jones Jr (1955), Determination of aromatic hydrocarbons in lubricating oil fractions by far UV absorption spectroscopy , p. 30. In Molecular Spectroscopy Report Conf. Institute of Petroleum, London. 

Determination of the dissociation constants of acids and bases from the change of absorption spectra with pH. The spectrochemical method is particularly valuable for very weak bases, such as aromatic hydrocarbons and carbonyl compounds which require high concentrations of strong mineral acid in order to be converted into the conjugate acid to a measurable extent. 

Wingen, L. M. Low, J. C. Pinlayson-Pitts, B. J. Chromatography, Absorption, and Pluorescence A New Instrumental Analysis Experiment on the Measurement of Polycyclic Aromatic Hydrocarbons in Cigarette Smoke, ... 

Fig. 20. Proposed photochemical mechanisms for the generation of acid from sulfonium salt photolysis. Shown ate examples illustrating photon absorption by the onium salt (direct irradiation) as well as electron transfer sensitization, initiated by irradiation of an aromatic hydrocarbon.

Another use is in various extraction and absorption processes for the purification of acetylene or butadiene and for separation of aHphatic hydrocarbons, which have limited solubiHty in DMF, from aromatic hydrocarbons. DMF has also been used to recover CO2 from flue gases. Because of the high solubiHty of SO2 iu DMF, this method can even be used for exhaust streams from processes using high sulfur fuels. The CO2 is not contaminated with sulfur-containing impurities, which are recovered from the DMF in a separate step (29). 

Photochromism Based on Triplet Formation. Upon absorption of light, many polycycHc aromatic hydrocarbons and their heterocycHc analogues undergo transitions to their triplet state which has an absorption spectmm different from that of the ground state (24). In rigid glasses and some plastics, the triplet state, which may absorb in the visible, has a lifetime of up to 20 seconds. 

DETERMINATION OF THE ABSORPTION CURVES OF AROMATIC HYDROCARBONS AND THE ANALYSIS OF BINARY MIXTURES... 

This exercise provides the opportunity of examining the absorption spectra of typical aromatic hydrocarbons and of investigating the possibility of analysing mixtures of hydrocarbons by ultraviolet spectrophotometry. 

Determination of the absorption curves of aromatic hydrocarbons and the analysis of binary mixtures 715... 

Sediment pollution. The concentrations of pollutants in the dated sediment cores have been determined in our laboratory by atomic absorption spectrophotometry (AAS). Donazzolo et al. (15) and Pavoni et al. (16) reported mainly heavy metal concentrations. Marcomini et al. (17) and Pavoni et al. (18) discussed the concentration profiles of organic pollutants such as chlorinated hydrocarbons and polycyclic aromatic hydrocarbons. 

Polycyclic aromatic hydrocarbons (PAH) are important air pollutants that have to be detected at very low concentrations. Fig. 2.4h shows the separation of a synthetic mixture of very low levels of PAH. They are barely detectable using uv absorption, but are easily monitored by fluorescence. 

Unlike methane and the other alkanes, aromatic hydrocarbons have absorptions in the UV part of the spectrum, and thus may be detected through UV spectrometry using silica fibers. This scheme is useful for "aromatic" water pollutants such as toluenes and xylenes with their absorption bands between 250 and 300 nm. Similarly, nitrate anion can be monitored (albeit with low sensitivity) in water via its UV absorption at 250 nm. 

HPLC has been used, with an ultraviolet absorption detector set for 254 nm, for the determination of aromatic hydrocarbons and with a flow calorimeter for the detection of all hydrocarbons. Increased sensitivity and decreased interference can be achieved with the ultraviolet absorption detector by measuring absorption at two wavelengths and using the ratios of the absorption at those wavelengths [28]. 

A reaction analogous to the formation of metal ketyls is the formation of negative ion-radicals not only from aromatic nitro compounds but also from aromatic hydrocarbons like naphthalene. These substances are highly colored and exhibit paramagnetic resonance absorption.128... 

Hashimoto, S. and Akimoto, H. (1989). UV absorption spectra and photochemical reactions of simple aromatic hydrocarbons in the cryogenic oxygen matrix. J. Phys. 

Ingestion of 12 g of endrin (dissolved in aromatic hydrocarbons) by a 49-year-old man in a suicide attempt caused convulsions persisting for 4 days death occurred after 11 days (Runhaar et al. 1985). Death occurred in 11 other cases following ingestion of endrin the time from administration to death ranged from 1 to 6 hours. In cases where endrin ingestion occurred with milk or alcohol, death occurred more rapidly (within 1-2 hours) presumably as the result of enhanced absorption that increased toxicity (Tewari and Sharma 1978). 

For 7i —> 7i4 transitions of aromatic hydrocarbons, the absorption transition moments are in the plane of the molecule. The direction with respect to the molecular axis depends on the electronic state attained on excitation. For example, in naphthalene and anthracene, the transition moment is oriented along the short axis for the So —> Si transition and along the long axis for the S0 —> S2 transition. Various examples are shown in Figure 2.3. 

For some aromatic hydrocarbons such as naphthalene, anthracene and pery-lene, the absorption and fluorescence spectra exhibit vibrational bands. The energy spacing between the vibrational levels and the Franck-Condon factors (see Chapter 2) that determine the relative intensities of the vibronic bands are similar in So and Si so that the emission spectrum often appears to be symmetrical to the absorption spectrum ( mirror image rule), as illustrated in Figure B3.1. 

Fig. B3.1. Illustration of the vibrational bands in the absorption and fluorescence spectra of aromatic hydrocarbons. Broadening of the bands will be explained in Section 3.5.1.

Jones, R. N. The Ultra-violet absorption Spectra of Aromatic Hydrocarbons. 

A very simple and effective method of increasing the intensity of Ti So transitions by several orders of magnitude was introduced by Evans 53-s5) Either the pure liquid or concentrated solutions of an aromatic hydrocarbon in chloroform were saturated with oxygen or nitric oxid at high pressures. The newly appearing absorption bands are proportional to the applied gas pressures from 0—100 atm. The So absorptions are in general well structured and the posi-... 

Craig, D. P., Ross, I, G. The triplet-triplet absorption spectra of some aromatic hydrocarbons and related substances. J. Chem. Soc. 1954, 1589 (1954). 

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