Mass Spectrometry of Some Organic Compounds

The thesis discusses the aspects of mass spectrometry related to organic chemistry. It is primarily concerned with involatile substances which cannot be studied by conventional mass spectrometry. Chapter I is a brief introduction and deals with the development of mass spectrometry from the early positive beam studies to its use in organic analysis. A study of furan (Chapter IIA) and benzfuran (Chapter IIB) systems is then discussed in an attempt to predict fragmentation patterns of the furan ring system in simple and complex structures. The cracking pattern of simple furans is considered along with the mass spectra obtained from some naturally occurring compounds, such as marrubiin and Columbia, which contain a substituted furan ring. Many of these natural products are involatile substances and a direct inlet system is used to obtain results. Some conclusions are drawn with reference to the identification of the furan system in a molecular structure and tentative structures are proposed for some of the abundant ions produced by electron impact. Chapter III is devoted to a series of naturally occurring tetracyclic antibiotics (the pyrromycinones and rhodomycinones) which include a polyhydroxyanthraquinone system in their structure. Correlation studies of the series of mass spectra obtained have been found useful in attempts to postulate structures for some related compounds which have been studied unsuccessfully by classical organic chemists. No worker has yet been able to predict the detailed stereochemical relationships in a compound from mass spectral data alone. Chapter IV discusses the limitations of mass spectrometry in this respect and demonstrates the use of the mass spectrometer to decide the overall "crowding" in a molecule. The chapter comments on the columbin-iso-columbin isomerism, the stereochemistry of rhodomycinone and its isomer and the positional isomerism which occurs in the chlorogriseophenones. Unsatisfactory results are usually obtained from compounds which are thermally unstable or which have a highly branched structure. However, although part of the cracking pattern obtained from derivatives of malonic acid may arise by thermal decomposition, it has been found possible to determine the molecular weight of such compounds by use of ions occurring at one mass unit greater than the parent ion. Correlation of the mass spectra of these compounds is again useful in determining structural features of some compounds which contain one or more quaternary centres