Chris Ramsden was born in Manchester, UK in 1946. He is a graduate of Sheffield University and received his PhD in 1970 for a thesis entitled ‘Meso-ionic Compounds’ (W. D. Ollis) and a DSc in 1990. Subsequently he was a Robert A. Welch Postdoctoral Fellow at the University of Texas (with M. J. S. Dewar)(1971-3), working on the development and application of semi-empirical MO methods, and an ICI Postdoctoral Fellow at the University of East Anglia (with A. R. Katritzky)(1973-6), working on the synthesis of novel heterocycles. In 1976 he moved to the pharmaceutical industry and was Head of Medicinal Chemistry (1986-1992) at Rhone-Poulenc, London. He moved to Keele University as Professor of Organic Chemistry in 1992, where he is now Emeritus Professor. His research interests include the structure and preparation of novel heterocycles, three-centre bonding in the context of the chemistry of betaines and hypervalent species, and the properties of the enzyme tyrosinase and related ortho-quinone chemistry. He was an Editor-in-Chief of ‘Comprehensive Heterocyclic Chemistry III’ and a co-author of ‘The Handbook of Heterocyclic Chemistry, 3rd Edn, 2010.

• PrefaceEric Scriven and Christopher A. Ramsden1. Heterocyclic mesomeric betaines: An overviewChristopher A. Ramsden2. Developments in the chemistry of 1,3a,6a-triazapentalenes and their fused analogsYingchun Wang, Tomas Opsomer and Wim Dehaen3. Type A mesoionic compounds (1980–2020)Christopher A. Ramsden and Florea Dumitrascu4. Type B mesoionic compounds (1980–2020)Florea Dumitrascu and Christopher A. Ramsden5. Meso-ionic compoundsW. David Ollis and Christopher A. Ramsden6. Meso-ionic heterocycles (1976–1980)Christopher G. Newton and Christopher A. Ramsden