Ultraviolet absorption molecules

As yet no quinazoline has been discovered which has any appreciable amount (say, 1%) of hydrated species in the neutral molecule,but several quinazolines were shown to contain a mixture of anhydrous and hydrated species in the cations. Anhydrous neutral molecules and anhydrous cations have an ultraviolet absorption spectrum of the general type C (Fig. 3) and hydrated cations, the type... 

Aminoquinoxaline exists predominantly as such rather than in the tautomeric imino form. This is indicated by a comparison of the basic strength of the 2-amino compound (pKo 3.90) and those of its fixed methylated tautomers, 2-dimethylaminoquinoxaline pKa 3.72) and l-methylquinoxalin-2-oneimine (pfCn 8.70). The ultraviolet spectrum of the neutral molecule of 2-dimethylaminoquinoxaline shows the expected bathochromic shifts compared to that of 2-aminoquinoxaline these spectra differ from the ultraviolet spectrum of the neutral molecule of l-methylquinoxalin-2-oneimine (Fig. 1). The mono-cations (68) and (69) derived from 2-aminoquinoxaline and l-methylquinoxalin-2-oneimine have a similar chromophoric system and show almost identical ultraviolet absorption (Fig. 2). 

Table 14.2. Ultraviolet Absorptions ofSome Conjugated Molecules Name Structure...

Photodissociation of the water molecule is a model system for both experimental and theoretical studies. Extensive experimental and theoretical studies have been performed on this system during the last few decades. Excitation in its longest wavelength ultraviolet absorption band around 150-200nm leads to the lowest excited singlet state Dissociation... 

CF2 is unique among carbenes because of its high stability and low reactivity. Investigations of the ultraviolet absorption spectrum of CF2 have led to estimates of roughly 10 milliseconds to one minute for the half-life of CF2 at pressures in the region of one atmosphere. The gas phase molecule does not react with BF3, N20, S02, CS2 or CF3I at 120 °C5 K The nature of CF2 is perhaps best presented in separate sections discussing its preparation, structure and physical properties, reaction chemistry, and reaction kinetics. 

Tsubomura, H. and Mulliken, R.S. (1960). Molecular complexes and their spectra. XII. Ultraviolet absorption spectra caused by the interaction of oxygen with organic molecules. J. Am. Chem. Soc. 82, 5966-5974... 

Ultraviolet absorption spectra appear when outer electrons of atoms or molecules absorb radiant energy and undergo transition to higher energy levels. These transitions are quantised and depends on the compound under examination. 

Those who applied quantum mechanics to atoms and molecules had a wealth of chemists data at hand well-defined bond properties including dipole moments, index of refractions, and ultraviolet absorption qualities and polarizability as well as well-defined valence properties of atoms in molecules. If one attempted to set up a wave equation for the water molecule, for example, there were 39 independent variables, reducible to 20 by symmetry considerations. But the experimental facts of chemistry implied or required certain properties that made it possible to solve equations by semiempirical methods. "Chemistry could be said to be solving the mathematicians problems and not the other way around," according to Coulson. 148... 

Kratschmer W, Fostiropoulos K, Huffman DR (1990) The infrared and ultraviolet absorption spectra of laboratory-produced carbon dust evidence for the presence of the Cgo molecule. Chem Phys Lett 170 167-170... 

Azulene. The absorption spectrum of azulene, a nonbenzenoid aromatic hydrocarbon with odd-membered rings, can be considered as two distinct spectra, the visible absorption due to the 1Lb band (0-0 band near 700 nm) and the ultraviolet absorption of the 1L0 band.29 This latter band is very similar to the long wavelength bands of benzene and naphthalene CLb) and shows the same 130 cm-1 blue shift when adsorbed on silica gel from cyclohexane.7 As in the case of benzene and naphthalene, this blue shift is due to the fact that the red shift, relative to the vapor spectra, is smaller (305 cm"1) for the adsorbed molecule than in cyclohexane solution (435 cm"1). Thus it would appear that the red shifts of the 1La band are solely due to dispersive forces interacting with the aromatic molecule, in agreement with Weigang s prediction,29 and dipole-dipole interaction is negligible. 

In very recent work Lagerqvist and Miescher272a continued the study of the vacuum ultraviolet absorption spectra of the isotopic molecules. The level L2Tl, v = 4, which was discerned in the spectra of the heavier isotopes only, coincides in 14NlsO with C2n, v = 6 and produces a strong three-level perturbation. The level perturbated in this... 

The observed ultraviolet absorption spectrum of l212 (for a display of the recorded spectrum see Section I.G of Wiberg s review article on the cyclopropyl group14) consists of three broad bands, of which the first (60,000 to 66,000 cm-1 7.44-8.18 eV) possesses a maximum at 63,000 cm 1 (7.8 eV oscillator strength/ 0.12), far to the red of most saturated absorbers and in the region of the n->n transitions of unsaturated molecules. This observation has... 

Laschewsky and Ringsdorf [203J studied the deposition and polymerisation of multilayers of alcohols and acids incorporating the diene group, — CH=CH—CH=CH— at the hydrophilic end of the molecule. The carbon atoms in this group are conventionally labelled from 1 to 4 starting from the hydrophilic end. Ultraviolet absorption studies of the polymerisation process indicate that initial polymerisation probably links atoms 1 and 4 in adjacent molecules respectively, thus creating a new... 

Light absorption by oxygen has been observed from the near infrared to the far ultraviolet. Absorption above about 2500 A. is of some interest in connection with proposed photochemical reactions of oxygen with some other molecules. For the formation of ozone, however, the middle and short ultraviolet region is of primary interest. 

For organic materials, ultraviolet absorption spectra are substantially determined by the presence of functional groups. Identical functional groups in different molecules may not absorb at precisely the same wavelength due to different structural environments which modify the local electric field. The magnitude of the molar extinction coefficient ( e ) for a particular absorption is directly proportional to the probability of occurrence of the particular electronic transition. Spectral features of some isolated chromophoric groups are presented in Table 2... 

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