25th International Congress of Pure and Applied Chemistry presents a compilation of papers covering a wide range of topics on applied and pure chemistry. This book discusses the challenges in the field of aromatic photosubstitution. Organized into six chapters, this book begins with an overview of the diverse reactions of aromatic molecules. This text then examines the pattern of specific RNA found in the human tumors, which showed a notable concordance with the predictions deducible from the animal system. Other chapters consider the methods of estimation of chemical fuels and describe the greenhouse effect arising from the burning of coal. This book presents as well an assessment of some features of the impact of quantum mechanics on chemistry. The final chapter deals with molecular beam and spectroscopic methods that allow a detailed investigation of several dynamical properties of single reactive collisions. This book is a valuable resource for chemists, theoreticians, research workers, and scientists.