Aromatic molecules in solution

The four-photon absorption cross section thus obtained is overall consistent with those of other aromatic molecules in solution described in literatures [4, 5]. 

Electrons can be ejected by ultra-violet light from aromatic molecules in solution (for a review, see Lesclaux and Joussot-Dubien, 1973). Recently Klaning et al. (1973) have reported that solvated electrons are formed from 2-naphthol by a 337-1 nm pulse from a nitrogen laser, and deduce that the rate of electron formation is higher than the rate of vibrational relaxation to the lowest excited singlet state. Since the electrons are relatively long-lived and take no further part in the ns time-scale reactions, the only effect they have upon the acid-base investigation is to necessitate a correction to the absorption spectra of the transient species under observation. 

Horrocks, A. R., Medinger, T., Wilkinson, F., New Accurate Method for Determining the Quantum Yields of Triplet State Production of Aromatic Molecules in Solution, Chem. Commurt. 1965, 452. 

Pulse Radiolysis Studies of Some Reactive States of Aromatic Molecules in Solution... 

Reactive states of aromatic molecules in solution may be observed directly by the pulse radiolysis method. Extensive investigations of both aromatic molecule ions (particularly the radical anions) and electronically excited states have provided new information about not only the radiation chemical processes but also the general kinetic behavior of these reactive intermediates. Absolute rate constants have been determined for many elementary processes such as energy transfer and electron and proton transfer reactions. 

Absolute rate constants for electron transfer reactions of aromatic molecules in solution have been determined by the pulse radiolysis method for three additional pairs of aromatic compounds. In two of these cases in which an electron transfer equilibrium is established, the rate constant for the back reaction has also been determined. The equilibrium constant has been estimated from the kinetic data. A correlation of the experimental rate constants with the theory for homogeneous electron transfer rates is considered. 

A bsolute rate constants for electron transfer reactions of some aromatic molecules in solution have been reported in our earlier work (2) using the pulse radiolysis method. The transfer of an electron from various radical anions to a second aromatic compound in solution was observed directly. Of the rate constants for nine donor-acceptor pairs investigated, two were found to be lower than the diffusion controlled values, and a correlation with such parameters as the reduction potential difference of the pair was considered. These measurements have been extended to additional transfer pairs for which the reduction potential difference is small. The objective of this work, in addition to furnishing new data for electron transfer rates, is to provide an adequate test of theories of the rate of homogeneous electron transfer in polar liquids (10, 11,12,13, 14, 15,16,17). 

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. 

Hermans,Jr.,J., Lohr.D., and Ferro,D. Treatment of the Folding and Unfolding of Protein Molecules in Solution According to a Lattic Model. Vol. 9, pp. 229—283. Hutchison, J. and Led with, A. Photoinitiation of Vinyl Polymerization by Aromatic Carbonyl Compounds. Vol. 14, pp. 49—86. 

Following the classical observation of Lewis and his school (29, 30, 34) of the photoionization of aromatic molecules in rigid solvents, Land, Porter and Strachan (25) proved such processes in the flash photolysis of aqueous solutions of phenols. It was suggested (7, 15, 25, 38) that the primary photochemical act involves electron ejection. 

Fig. 13. Absorption spectra of triplet states of aromatic molecules in acetone solution (from ref.

The X-ray structure of l-piperidino-2,4-dinitrobenzene was published (95MI801). The piperidine ring exhibits a slightly distorted chair conformation the N-atom is almost in a plane due to the partial C,N double bond, and the aromatic ring shows a slight boat deformation with the o/p-nitro groups twisted out of plane. UV and NMR data indicate that the molecule in solution presents a conformation similar to that in the solid state. In the crystalline anhydrous N-methylpiperidine betaine 86 (cf. Scheme 33) the piperidine ring adopts the usual chair conformation... 

One is compelled to conclude that the study of the magneto-optical behaviour of strobilic molecules in solution does not seem to be directly uti-lizable as a criterion of strobilism. But the main interest of this conclusion is that it may be generalized to other magnetic properties of matter, and particularly to the N.M.R. field so many people have tried to measure the aromaticity of a molecule by N.M.R. studies in solution. 

The theory of rotation effects on prolate luminescent molecules in solution and its experimental verification have been developed and compared. Generalized diffusion equations for the rotational motion of an asymmetric rigid motor have been used to given an expression for steady-state fluorescence depolarization. " The radiationless transition from the first excited singlet state of Eosin has been measured by optoacoustic relaxation, and the absolute fluorescence quantum yields of organic dyes in poly(vinyl alcohol) have also been measured by the photoacoustic method. The accuracy of the method has been discussed in the latter paper. Actinometry in flash photolysis experiments has been assisted by new measurements on the extinction coefficient of triplet benzophenone. Matrix-isolation fluorescence spectrometry has been used to detect polycyclic aromatic hydrocarbons from gas chromatography. ... 

Radical cations derived from Mrfluoro aromatic molecules were first described by Bazhin et al. > The species were made in super acid or oleum solutions and were unambiguously characterized by ESR spectroscopy. Such species have also been proposed as interm tates in the oxidative fluorination of aromatic molecules by high-valent metal fluorides such as cobalt trtfluoride, by bromine trifluoride, and by xenon difluoride. They have also been invoked in the electrochemical fluorination of aromatic molecules in the presence of F. Salts of such radical cation species were unknown prior to the synthesis of C6F6 AsF6 in these laboratories. ... 

Classical SDAs such as alkylamines or alkylammonium cations, which were mentioned in the second part of this article, do not possess special properties which would make them of interest for the construction of materials. Aromatic molecules, in contrast, can be equipped with many different properties. For example, they can act as chromophores, may possess large hyperpolarizabilities (for NLO applications such as SHG, cf the pNA molecule) or stabilize special electronic structures like radicals. However, aromatic molecules are notoriously poor SDAs. One of the few exceptions is pyridine. The hydrothermal treatment of a pyridine - HF - H2O silica solution at 190°C, for instance, results in the formation of large crystals of dodecasil 3C, a clathrasil with small cages. These crystals, which can grow to millimeter size, are acentric at room temperature and exhibit SHG, although the effect is only weak [37]. 

The reactions of organic molecules in solution are related to gas phase electron affinities and electronegativities. Anions are often intermediates in such reactions. The electron conduction of polymers is related to the electron affinities of the components. The theoretical calculations of electron affinities of aromatic hydrocarbons and the effect of substitution on electrons affinities and gas phase acidities are important to organic chemistry. Pseudo-two-dimensional Morse potentials have been used to represent the dissociation of organic molecules and their anions [18]. 

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