Introduction 1 John A. Joule and John P. Richard Department of Chemistry The University of Manchester Manchester UK M13 9PL Department of Chemistry State University of New York at Bu.alo Bu.alo NY 14260—3000 USA The reporters for this year’s volume have done an excellent job of identifying and discussing the most important .ndings from an ever-increasing volume of literature. We have continued to increase the scope of coverage of important topics in physical organic chemistry by the addition of a new report on ‘Gas phase organic ion—molecule reaction chemistry’ by W. Y. Feng and S. Gronert. This chapter emphasizes the valuable information about reaction mechanisms that can be obtained from studies in the absence of solvent. The coverage of enzyme reaction mechanisms by N.G. J. Richards and the reactions of radical ions by D. E. Falvey that was introduced last year has been continued in this volume. Advances in NMR spectroscopy relevant to the organic chemist are reported once again by B. A. Salvatore and I. Alberts has written another engaging report on the progress in theoretical organic chemistry. Finally J. C. Fishbein has replaced I. W. Ashworth as the reporter on polar reaction mechanism. Professor Fishbein presents an admirable overview of the important work which has resulted in the continued re.nement in our understanding of the mechanism for heterolytic reactions in solution. Following the pattern which was established last year this year’s volume sees the .rst biennial report on ‘Natural Products’ which is to alternate with biennial reports on ‘Biosynthesis’ and the .rst biennial report on ‘Natural polymers’ which is to alternate with ‘Man made polymers’.We have continued coverage of synthetic chemistry using the inevitably occasionally overlapping topics of ‘Pericyclic Methods’ ‘Heteroatom Methods’ ‘Radical Methods’ ‘Enzyme Chemistry’ and ‘Protecting Groups’.The enormous and hugely important area of organometallic chemistry is subdivided into discussions of ‘Stoichiometric Applications’ and ‘Catalytic Methods’. The traditional ‘Aromatic Chemistry’ and ‘Heterocyclic Chemistry’ topics are covered separately. It is worth re-iterating that it is impossible to devise subdivisions which would ensure no overlap between reports especially given the short time available for editing given our continuing aim to produce Annual Reports as soon after the year being covered as possible. 1 Annu. Rep. Prog. Chem. Sect. B 1999 95 1 MMMM Annu. Rep. Prog. Chem. Sect. B 1999 95 0—00 2 3 Annu. Rep. Prog. Chem. Sect. B 1999 95 1