This book covers the basic concepts of acids and bases, and explores the inductive effect, resonance effect, steric effect, and solvent effect, among others, on the strength of acids or bases, as well as hydrogen bonding. It also discusses the difficulties of proposing a suitable mechanism for any reaction. The book also presents the structure, geometry, isolation and reactions of different intermediates (such as carbocations, carbanions, free radicals, carbine, nitrene, benzyne, diopolar species like nitrile oxide, nitrile imines and dienophles like α-nitrosoolefin and α-iminoolefins), supported by suitable examples.