Spectral and Theoretical Studies

Spectral and Theoretical Studies of Aziridines. - Optically active 2-alkyl-aziridines (268 R = H or Me, R = Me, Pr, or Bu ) have been prepared from their corresponding L-amino-acids and their chiroptical properties recorded. From their o.r.d. and c.d. spectra it was concluded that a negative Cotton 

Maat and R. W. Wulkan, Reel. Trav. Chim. Pays-Bas, 1981, 100, 204. 

The proton-accepting abilities of ds-(269 R = H, Me, or PhCHj R = H or NO2) and of trans- 269] R = H, Me, or PhCHj R = H, Br, or NO2) have been estimated, using the i.r. spectral shifts that are induced by these aziri-dines is phenol, 4-bromophenol, and trichloroacetic acid. The cw-isomers reacted with all three proton donors but rw s-isomers only with CCI3COOH. The absence of complexation for the fra/is-isomers was attributed to intramolecular hydrogen-bonding (when R is H) and to steric hindrance when R is Me or PhCH2. 

Two theoretical studies on the structure of aziridine have been published, one relating to the effect of hyperconjugation on the barriers to the inversion of nitrogen and the other to the structures of aziridine-enamines. The reaction by which (270 R = H, Me, or NH2) are hydrolysed to cis- and to trans- 27 ) has been subjected to ab initio calculations. Theoretical predictions have been found to agree with experimental results. 

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Among spectral and theoretical studies on fluoroheterocycles are n.m.r. data on 2-, 3-, and 4-fluoropyridines and the corresponding pyridinium ions, ... 

To date only a limited number of hydridopalladium complexes have been successfully isolated and characterized unequivocally. The different synthetic routes, as well as structural, spectral, and theoretical studies of discrete hydridopalladium species, have been reviewed extensively in 1996. " With the notable exception of the unusual zerovalent complexes (such as [PdHJ ), almost all of the hydridopalladium complexes reported so far have been monohydride complexes coordinated by phosphine ligands. 

Very recently there has been an experimental and theoretical study of electronic substituent effects in 4-aminoaryl (4-substituted aryl) sulfones146. PMR, 13C NMR and infrared measurements were involved and semi-empirical all-valence CNDO/2 calculations, with and without sulfur d orbitals, were carried out. Various correlations between spectral results and substituent constants are presented. There is good agreement between experimental and theoretical data, which does not depend on the inclusion or exclusion of the sulfur d orbitals from the calculations. 

However, there is a critical lack of information on this system, mainly due to insufficient studies of its spectral signatures, which makes it difficult to insert this molecule with confidence in the astrochemical schemes. During these years, only a few experimental and theoretical studies were performed, aiming to the different spectra useful for interstellar identification and chemistry. Still a lot remains to do. 

While excited-state properties of monomeric carotenoids in organic solvents have been the subject of numerous experimental and theoretical studies (Polfvka and Sundstrom 2004), considerably less is known about excited states of carotenoid aggregates. Most of the knowledge gathered so far stems from studies of aggregation-induced spectral shifts of absorption bands of carotenoid aggregates that are explained in terms of excitonic interaction between the molecules in the aggregate. 

Periodic spectral phase-modulation functions have been used in numerous experiments and theoretical studies on coherent control of atoms [75-79] and molecules [24, 25, 42, 68, 73, 80-85]. Applying a sinusoidal phase-modulation function of the form... 

The relatively simple spectral and kinetic behavior of 10-CPT in methanol-water mixtures can be described by a well-developed reversible diffusion influenced two-step model (Scheme 1). We successfully applied this scheme in the experimental and theoretical studies of reversible ESPT processes in solution. 

The synthesis of NH- and Af-vinylpyrroles from ketones (ketoximes) and acetylenes has stimulated physicochemical and theoretical studies of ketoximes as well as pyrroles and N-vinylpyrroles. The easy access to diversely substituted representatives of pyrrole series made it possible to systematically examine the structural effect on their reactivity and spectral properties. This section is a concise account on the research related to NH- and N-vinylpyrroles originated from the reaction of ketones with acetylenes along with investigation of stereoelectronic properties of intermediate ketoximes. 

Korzeniowska-Sobczuk A, Hug GL, Carmichael I, Bobrowski K. (2002) Spectral, kinetics, and theoretical studies of radical cations derived from thioanisole and its carboxylic derivative./Pfryr Chem A 106 9251-9260. 

The project Carl gave me was to build a sensitive instrument to search for luminescence from the permanganate ion, which had been the subject of a series of experimental single crystal absorption spectral studies and theoretical studies in the laboratory [6]. The spectrometer was built, but after repeated attempts using a range of crystals, excitation conditions and temperatures, no luminescence was detected. All subsequent efforts by others have confirmed this failure [7], under laser irradiation in iodide lattices some emission has been detected, but this is derived from the manganese ion MnO, 2 produced by a photoredox process [8]. This left me without many results to show for my year s work. I made some measurements on the intensely luminescent alkali metal platinocyanides but this did not lead to any new insights. 

Chemical lasers are complex nonequilibrium molecular systems governed by an intricate interplay between a variety of chemical, radiative, and collisional relaxation processes. Many of their kinetic properties are reflected by the temporal, spectral, and power characteristics of the out-coupled laser radiation. For example, threshold time measurements and other gain experiments have provided detailed information on vibrational distributions of nascent reaction products. Another, more qualitative, example Single-line and simultaneous multiline operation indicate, respectively, whether the lasing molecules are rotationally equilibrated or not. Besides their practical applications, chemical lasers are widely used as means of selective excitation in state-to-state kinetic studies. On the other hand, many experimental and theoretical studies have been motivated by the wish to understand and improve the mechanism of chemical laser operation. 

Comparison of experimental and theoretical studies of the solution absorption and luminescence spectra of lanthanide and actinide ions is the focus of this chapter. In aqueous solutions, the most stable oxidation state of lanthanide ions is 3+, but actinide-ion formal oxidation states ranging from 2+ to 7 -I- are known (Seaborg and Loveland 1990). Actinide elements heavier than plutonium exhibit more lanthanidelike behavior, however, in that 3-1- is their most stable formal oxidation state in aqueous solution. The visible and near-infrared absorption spectra of trivalent lanthanide and actinide ions in solution provide such rich detail that the spectra may fairly be said to fingerprint the ion for identification. The abundance of sharp spectral features long confronted theoretical and experimental spectroscopists with difficult problems. The efforts of numerous workers have provided interpretation of many aspects of the spectra of these f-transition elements significant challenges remain. 

Gewirth AA, Cohen SL, Schugar HJ, Solomon El. 1987. Spectroscopic and theoretical studies of the unusual EPR parameters of distored tetrahedral cupric sites correlations to X-ray spectral features of core levels. Inorg Chem 26 1133-1146. 

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