Mass spectrometry does not represent a novel physical tool in geochemical research. Petroleum chemists have made use of mass spectrometry for many years in the analysis of the components of crude oil. Such applications were concerned primarily with quantitative analytical problems, with emphasis on the determination of compound types which constitute a given petroleum sample, and the number of papers on this subject is legion. In recent years — and the developments of recent years are primarily the subject of this review — the tremendous potential of mass spectrometry for the solution of structural problems has been recognized by the organic chemical community in general, and since then rather extensive and sophisticated use has been made of the technique for structural studies on organic compounds. The widespread application to problems of organic chemistry has in turn sparked intense interest in mechanistic studies on the fragmentation processes of ionized molecules in the vapor state. Practical applications and fundamental studies combined have thus within a few years produced a substantial body of information on the nature of mass spectra of organic compounds, information which makes feasible a fruitful exploitation of mass spectrometric data for the solution of structural problems. The considerable number of volumes [1–10] addressing themselves wholly or in part to the application of mass spectrometry to problems of organic and natural products chemistry reflects the pace of progress and the scope of this field; it is recommended that these works be consulted for a thorough initiation into all phases of organic mass spectrometric research and its ramifications.

Mass Spectrometry in Organic Geochemistry

Mass spectra and organic analysis—II

Two genes (ubiB and ubiD) concerned with two successive reactions in ubiquinone biosynthesis in Escherichia coli were mapped and found to be closely linked. Mutant strains of E. coli carrying the ubiB− and ubiD− alleles were shown to accumulate 2-octaprenylphenol and 3-octaprenyl-4-hydroxybenzoic acid, respectively. These compounds were isolated and identified by using nuclear magnetic resonance and mass and infrared spectroscopy. Cell extracts from the mutant strain carrying the ubiD− allele lack 3-octaprenyl-4-hydroxybenzoate decarboxylase activity.

Biosynthesis of Ubiquinone in Escherichia coli K-12: Location of Genes Affecting the Metabolism of 3-Octaprenyl-4-hydroxybenzoic Acid and 2-Octaprenylphenol

While in the early days of organic mass spectrometry the ortho effect was preferentially used as a diagnostic tool for structure elucidation, the recent research activities have concentrated on mechanisms and related aspects. Among these the following were the most important topics: hydrogen transfer and especially the question of concerted or multistep reaction; the influence of the structure on the selectivity of hydrogen migration via higher-membered transition states; the apparent cleavage of carbon/heteroatom bonds induced by hydrogen transfer; the redox processes which formally correspond to photochemical transformations, but which are completely different according to the reaction mechanisms; the different types of cyclization reactions; and the field of exchange processes preceding or accompanying unimolecular decompositions of ions in the gas phase. If a prognosis concerning the future activities in the field of electron impact induced ortho effects may be risked, the following aspects will probably become more important in addition to the topics discussed in this review:

(i)

Kinetic studies in the time range of nanoseconds to elucidate the time dependence of the different ortho effect reactions;




(ii)

ion/molecule reactions with the scope to obtain more information concerning the reactivities of open and closed shell systems;




(iii)

comparative studies in the fields of mass spectrometry, photochemistry and electrochemistry.

R. S. Gohike

Papers

Mass Spectrometric Analysis. Aromatic Acids and Esters