Interpretation of Spectroscopic Data

Hartfield, R.J., Interpretation of spectroscopic data from the iodine molecule using a genetic algorithm, Appl. Math. Comp., 177,597,2006. 

Some future directions in inorganic photochemistry have been outlined by Adamson (56). A pessimistic picture of the practical uses of solar energy conversion systems is painted, but a rosy view of the academic future of the subject is held. It is anticipated that there will be further examination of thermally equilibrated excited (thexi) states—their lifetimes, and spectroscopic and structural properties—and an extension of present efforts to organometallics and metalloproteins is also envisaged (56). The interpretation of spectroscopic data from excited states will continue to be controversial and require future experimentation (57). 

The cytostolic phospholipase A2 inhibitor tauropinnaic acid (229) was isolated from the Okinawan bivalve Pima muricata (pen shell). The structure and stereochemistry at all but one centre were elucidated by interpretation of spectroscopic data [234]. 

Sulfircin (369), an antifungal sesterterpene sulfate was isolated as the iV,iV-dimethylguanidinium salt from a deepwater Ircinia species and its structure was determined by X-ray analysis [324]. Two sesterterpene sulfates, hipposulfates A (370) and B (371), were isolated from Hippospongia cf. metachromia from Okinawa and their structures were elucidated by interpretation of spectroscopic data. Both compounds possess an enolsulfate functionality [325]. 

The use of molecular mechanics as an aid in the interpretation of spectroscopic data is outlined in more detail in Chapter 9. One of the most rapidly developing applications of molecular mechanics is the use of the structures to aid in the analysis of multidimensional NMR spectroscopy125,261. This is particularly pertinent to the study of metal-macromolecule interactions where the spectroscopic data often have too low an observation/variable ratio to allow an unequivocal determination of the structure. Therefore, an additional source of structural information is needed. To date, there have been a limited number of studies involving metal ions but this area is likely to become a very important application of structural information from molecular mechanics studies (see also Chapter 9). 

In many places elsewhere in this book we describe the analysis of spectra, the definition and determination of molecular parameters from the spectra, and the relationships between these parameters and the wave functions for the molecules in question. Later in this chapter we will outline the principles and practice of calculating accurate wave functions for diatomic molecules. Before we can do that, however, we must discuss the calculation of atomic wave functions the methods originally developed for atoms were subsequently extended to deal with molecules. This is not the book for an exhaustive discussion of these topics, and so many accounts exist elsewhere that such a discussion is not necessary. Nevertheless we must pay some attention to this topic because the interpretation of spectroscopic data in terms of molecular wave functions is one of the primary motivations for obtaining the data in the first place. 

Computational methods have been widely used as valuable tools for structure elucidation, investigation of reaction mechanisms, and interpretation of spectroscopic data. The representative applications in the area of heterocyclic compounds described in this chapter with group 14 heteroatom are presented in Table 1. 

In certain cases, structure elucidation of aryltetralin lignans has only been established by total synthesis of the ( )-compounds. Noteworthy in this respect have been the constituents of Phyllanthus nlruri Linn. (Euphorbiaceae), extracts of which have been used medicinally (in treatment of asthma, jaundice and bronchial infections) (140). Considerable confusion resulted mainly from differing interpretations of spectroscopic data, and at least five different structures were proposed for the major constituent, hypophyllanthin. The structure of the aryltetralin constituents established by unequivocal synthesis (141) are shown in Scheme 30 they were given the names hypophyllanthin (1411. nirtetralin (1421. phyltetralin (1431 and lintetralin (1441. 

Quantum chemical calculations on metal clusters in zeolite A [12] and semi-empirical ligand field interpretations of spectroscopic data of transition metal ions [6] have proven to be successful in structural characterizations of molecular sieves and their guest species. The present tendency in catalysis towards a more fundamental approach justifies the expectation that ESR, combined with other spectroscopic techniques, will become important. However, this requires an accurate and unambiguous parameterization of the ESR spectra. The parameter set thus obtained forms a firm basis for a theoretical investigation of the coordination environment of the paramagnetic entity. 

The interpretation of spectroscopic data for the identification and structure elucidation of organic compounds is largely an empirical process and relies heavily on the use of previously accumulated reference data. Compilation of computer-readable spectroscopic data bases is nowadays feasible because most commercially available spectrometers have small built-in computers for the digital acquisition of measured spectroscopic data they are also equipped with a suitable mass storage device to store spectra or selected spectral data, or they provide the facility to transfer the recorded spectra to a more powerful external computer. If the computer-readable spectroscopic data are suitably organized, the analyst is provided with a very powerful tool for the identification of a compound, a group of compounds or a structure by means of suitable software, thereby avoiding the slow and tedious manual work otherwise involved [67,69]. 

Production, storage, treatment, evaluation, expolitation and interpretation of spectroscopic data is strongly connected with intensive use of computers. Modern spectroscopy - as many other disciplines - would not be possible without the tremendous developments in hardware and software during the last decades. Most of the mentioned aspects are treated in the three parts of this section, although the authors have focuses on different subjects. 

Intelligent computer assisted interpretation of spectroscopic data should be based on the knowledge from large structure oriented data collections. Both the inspection of spectral features and the statistical evaluation of similar structures (from library searches) can provide a set of probability ranked substructures which are readily assembled to target structures. The idea of substructure analysis allows the chemist to combine the results of different interpretation strategies, different databases and different spectroscopic methods to yield the structural information desired. Thus in a multidimensional data system hke SPECINFO structural noise can be effectively suppressed, if all information available in the spectroscopic laboratory is combined in a central intelligent computer system. 

The ideal gas heat capacity can be quite well derived by the interpretation of spectroscopic data. But in the recent years, the measurement of the speed of sound has more and more become the favorite method [53-55]. The relationship between dp and the speed of sound w of an ideal gas is (see Section 3.2.6, Eq. 3.99 and... 

Discuss how computational methods can help in the interpretation of spectroscopic data. 

The lanthanide compoimds imder consideration have a large number of excited electronic states (Kaledin et al., 1996a), which complicates the interpretation of spectroscopic data. In particular, the molecular constants for the groimd state cannot be always determined. The available data should be preliminarily tested for reliability, and missing data should be completed. To this end, a semiempirical approach is possible in which the results are checked for correspondence with the known principle of the change in a given parameter in a series of related compoimds. 

X0 compounds are supported on oxide surfaces, again vibrational (Raman in particular) and optical spectroscopies provided significant information for structural assignments. OH groups, oxide ions and oxo-species may thus be considered as intrinsic probes. The characterization of anion vacancies (Lewis acid sites) can be performed using probe molecules (CO, NH3, pyridine, etc.). The use of model molecular compounds has almost completely been confined to their application as reference compounds (alcohols, carbonates, bicarbonates, carbonyls, carboxylates, Lewis acid-base adducts, 0x0-compounds, etc.) for the interpretation of spectroscopic data. 

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