XXIIIrd International Congress of Pure and Applied Chemistry, Volume 4 contains papers presented at the XXIIIrd International Congress of Pure and Applied Chemistry held in Boston, USA on July 26-30, 1971. This book is organized into two main topics—short-lived intermediates, free radicals and homolytic mechanisms, and ion pair processes. This publication specifically discusses the chemically induced dynamic nuclear polarization, formation of radical anions by the attack of radicals upon anions, and high temperature organic reactions by flash vacuum pyrolysis. The structure-reactivity relationships in the chemistry of aliphatic free radicals, medium effects on radical-radical reactions, and oxidation of alkyl radicals by metal complexes are also described. This text likewise considers the end group association and complexation in anionic polymerization and reversal of singlet and triplet states in aromatic dianions with trigonal symmetry. This compilation is useful to chemists and specialists researching on pure and applied chemistry.