Spectral data, structural information

This chapter extends the information provided by the two preceding reviews (1,2) to the literature that appeared within the years 1976-1986, focusing on spectral data, structural elucidation, synthesis, biosynthesis, and pharmacology. Some references that appeared in the foregoing reviews are omitted from this chapter with exception of those related to the present treatise. Although previously presented in Volume 16 of this treatise (2), the numbering system of the hasubanan skeleton (la) and the hasubanalactam skeleton (lb), which is used in this chapter except for the most part of Section V, is represented anew. 

The spectral data provide information about the structure of a-acetoxydibenzylnitrosamine (VII). The high frequency (1780 cm ) for the carbonyl group in the infrared spectrum (Fig. 9) is consistent with this structure ( ) and the introduction of the chiral center at the benzylic position causes the methylene of the other benzyl ic substituent to be diastereotopic and appear in the nmr spectrum as an AB quartet. The center of the quartet... 

In the last two paragraphs we have reviewed some of the schemes proposed to produce music from spectral or structural information of various types of molecules. This is possible only because such data are, in most cases, not distributed at random there are hidden regularities, whose perception may be enhanced by musical transcription. This topic can be considered as taking place in the wide area known as "pattern recognition". It is often easier for us to recognize a pattern from an auditive transcription than from a visual picture. 

Chemical Abstracts Service Information System Electronic Laboratory Notebooks Internet Internet-based Computational Chemistry Tools Laboratory Information Management Systems (LIMS) Online Databases in Chemistry Spectroscopic Databases Standard Exchange Formats for Spectral Data Structure and Substructure Searching. 

Circular Dichroism Electronic Computer Graphics and Molecular Modeling Electronic Laboratory Notebooks Electronic Publishing of Scientific Manuscripts Factual Information Databases Internet Molecular Models Visualization Object-oriented Programming Online Databases in Chemistry Standard Exchange Formats for Spectral Data Structural Similarity Measures for Database Searching. 

Chemometrics Multivariate View on Chemical Problems Combinatorial Chemistry Factual Information Databases Fuzzy Methods in Chemistry Infrared Data Correlations with Chemical Structure Infrared Spectra Interpretation by the Characteristic Frequency Approach Inorganic Chemistry Databases Inorganic Compound Representation NMR Chemical Shift Computation Ab Initio NMR Chemical Shift Computation Structural Applications NMR Data Correlation with Chemical Structure Online Databases in Chemistry Spectroscopy Computational Methods Standard Exchange Formats for Spectral Data Structure and Substructure Searching Structure Determination by Computer-based Spectrum Interpretation Structure Generators Synthesis Design. 

In contrast to IR and NMR spectroscopy, the principle of mass spectrometry (MS) is based on decomposition and reactions of organic molecules on theii way from the ion source to the detector. Consequently, structure-MS correlation is basically a matter of relating reactions to the signals in a mass spectrum. The chemical structure information contained in mass spectra is difficult to extract because of the complicated relationships between MS data and chemical structures. The aim of spectra evaluation can be either the identification of a compound or the interpretation of spectral data in order to elucidate the chemical structure [78-80],... 

Because protein ROA spectra contain bands characteristic of loops and turns in addition to bands characteristic of secondary structure, they should provide information on the overall three-dimensional solution structure. We are developing a pattern recognition program, based on principal component analysis (PCA), to identify protein folds from ROA spectral band patterns (Blanch etal., 2002b). The method is similar to one developed for the determination of the structure of proteins from VCD (Pancoska etal., 1991) and UVCD (Venyaminov and Yang, 1996) spectra, but is expected to provide enhanced discrimination between different structural types since protein ROA spectra contain many more structure-sensitive bands than do either VCD or UVCD. From the ROA spectral data, the PCA program calculates a set of subspectra that serve as basis functions, the algebraic combination of which with appropriate expansion coefficients can be used to reconstruct any member of the... 

Stylotelline (23) is a constituent of a Stylotella sp. collected offshore in New Caledonia. 13C NMR spectra involving 2D NMR techniques provided the bulk of information leading to its structure. The absolute configuration was demonstrated after the tertiary isocyano group was removed to yield the known conjugated diene, ( + )-d-selinene (24). Optical rotation and spectral data of the transformation product were identical in all respects to those of the corresponding product obtained from eudesmols [42], Although neither the isothiocyanato nor the formamido compounds were isolated, the latter was prepared, which allowed an nOe observation between the axial C-3 and the amide protons. 

In addition to the indications of an octahedral trans effect presented, there exists structural information in the form of bond lengths and spectral data similar to that described earlier for square planar complexes. Although the trans effect in octahedral complexes is not the dominant influence that it is in square planar complexes, there is no doubt that there is such an effect. 

A full range of spectral data was routinely reported for each of the new compounds isolated. Nuclear magnetic resonance (NMR) spectroscopy and X-ray crystallography have essentially only been used as methods of structure determination/ confirmation and the results are unexceptional. The use of mass spectrometry in these series of compounds has been mainly confined to molecular ion determination. Ultraviolet (UV), infrared (IR), and Raman techniques have been used for confirmation of structures, but no special report has been published. The major data in this field are well documented in CHEC-II(1996) and will not be reproduced in this chapter. Over the last decade, all these methods played a major role in establishing the structure, but did not provide new interesting structural information on these bicyclic systems. In consequence, these methods are not considered worthy of mention in detail here. 

Vibrational spectroscopy has been widely applied in the study of LDHs [161,162] but a somewhat confusing variety of spectral data and interpretations have appeared in the literature, hi this section, we focus on the information that can be obtained regarding the structure of the interlayer anions. The unperturbed carbonate ion has point symmetry Dsh. Group theoretical analysis predicts four normal modes the vi symmetric stretch of Aj symmetry at 1063 cm the V2 out of plane bend of A 2 symmetry at 880 cm the V3 asymmetric stretch of E symmetry at 1415 cm , and the V4 in plane bend of E symmetry at 680 cm [22]. The V2 mode is IR active only, the vi mode is Raman active only, whilst the two E modes are both IR and Ra-... 

Module 1, Determination of Chemical and Structural Information on the Sample. The task of Module 1 is to provide non-chromato-graphic data for analytes prior to specification of the chromatographic method. Data bases have been developed for pK values of organic molecules, isoelectric points of proteins, and fluorescence spectral properties of organic molecules. 

We examine the derivation of information about molecular structure and properties from analysis of pure rotational and vibration-rotational spectral data of diatomic molecular species on the basis of Dunham s algebraic formalism, making comparison with results from alternative approaches. According to an implementation of computational spectrometry, wave-mechanical calculations of molecular electronic structure and properties have already played an important role in spectral reduction through interaction of quantum chemistry and spectral analysis. 

Following the receipt of all available information including any spectral data, how the request for assistance is handled by the group(s) responsible for providing structural characterization will depend, in part, on how structure elucida-tion/characterization function is organized, which can vary from company to company and even between sites within a single company. The most prominent models for the organization of structure characterization units within the pharmaceutical industry are very briefly considered in Section 5.1.1. 

As reported in <1996GHEC-II(7)283>, no specific study on the mass spectra of these classes of compounds has been reported, although this analytical method has only been used as a tool for structure elucidation or reference without critical analysis. Some examples are reported in <1996GHEC-II(7)283>. Further information on the MS of heterocycles can be found in <2001MI1>. The mass spectral data for imidazopyridines, pyrazolo[3,4- ]pyridines, oxazolo-pyridines, ioxazolopyridines, isothiazolopyridines, 377-1,2-dithiolo[3,4- ]pyridines, and l,3-dithiolo[4,5- ]pyridines were reported in <1996GHEG-II(7)283>, but there have been no further reports in this area. 

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