1. The Problem of Tautomerism.- 1. Tautomerism as Dynamic Isomerism.- 1.1. Molecular Structure and Isomerism.- 1.2. Bond Rupture Formation Criterion.- 1.3. Tautomerism and Rearrangements.- 1.4. Thermodynamic and Activational Scale of Tautomeric Processes.- 2. Degenerate Tautomerism.- 3. Methods for Investigating Tautomeric Systems.- 4. Butlerov's and Laar's Tautomeric Systems.- 5. Tautomerism and the Mechanisms of Organic Reactions.- 6. Classification of Tautomeric Reactions.- 6.1. Prototropy.- 6.2. Metallotropy.- 6.2.1. ?, ?-Transfers.- 6.2.2. ?, ?-Transfers.- 6.2.3. ?, ?-Transfers.- 6.3. Anionotropy.- 6.4. Valence Tautomerism.- 6.4.1. ?-Valence Tautomerism.- 6.4.2. ?, ?-Valence Tautomerism.- 6.4.3. ?-Valence Tautomerism.- 7. Conclusion.- References.- 2. Carbonotropy.- 1. The Problem of Carbonotropy.- 1.1. General Principles.- 1.2. Choice of a Migrant.- 2. Sigmatropic Acyl and Aryl Rearrangements.- 2.1. Acyl 1,3-Rearrangements.- 2.2. Aryl 1,3-Rearrangements.- 2.3. 1,5-and 1,7-Acyl Rearrangements.- 3. Acylotropic Tautomerism.- 3.1. Tautomeric 1,3-Acyl Rearrangements of the N,N?-diarylamidine Derivatives.- 3.2. Stereochemistry of Acyl Migration.- 3.3. Tautomeric 1,5-Acyl Rearrangements of O-Acylenols of 1,3-Diketone.- 3.4. Acylotropy of 9-Acyloxyphenalen-l-ones.- 3.5. Tautomerism of 2-Acyloxytropones.- 4. Tautomeric Rearrangements of Aryl Groups.- 4.1. 1,3-Rearrangements of Aryl Groups.- 4.2. O,O?-Migrations of the Aryl Groups in O-Aryl Derivatives of Tropolone and the Synthesis of Bipolar Spiro- ?-Complexes.- 4.3. Valence Tautomerism of O-Aryl Ethers of o-Hydroxybenzaldehydes and their Imines.- 5. Carbonotropic Tautomerism in Ions, Radicals and Cyclopolyenes.- 5.1. Acylotropic and Arylotropic Rearrangements in Anions.- 5.2. Acylotropy in Phenoxyl Radicals.- 5.3. Tautomeric Rearrangements of Carbocations.- 5.4. Acyl and Aryl Migrations in Cyclopolyenes.- References.- 3. General Principles of the Design of Tautomeric Systems.- 1. Possibilities of Quantum Mechanical Prediction of Tautomeric Reactions.- 1.1. Theoretical Evaluation of Free Energies of Tautomeric Equilibria.- 1.2. Theoretical Calculation of Activation Energies of Tautomeric Reactions.- 2. Stereochemical Approach to the Design of Tautomeric Compounds.- 2.1. Intramolecular Coordination of the Migrating Group.- 2.2. Cyclic Electron Transfer in the Sigmatropic Reaction and Multigraphs of Tautomeric Systems.- 2.3. Orbital Symmetry and Activation Barriers of Sigmatropic Shifts between Heteroatomic Centers.- 2.4. Steric Demands of the Transition State Structures.- 2.4.1. The Bond Configuration of the Central Atom.- 2.4.2. Structure of the Molecular System Connected with a Migrant.- 2.4.3. Addition-Rearrangement-Elimination (AdRE) Mechanism.- 2.5. Analogy in Steric Requirements between Fast Intramolecular, Enzymic and Topochemical Reactions.- References.- 4. The Mechanisms of Nucleophilic Substitution at the Main Group Element and Design of Intramolecular Tautomeric Systems.- 1. Tautomeric Rearrangements of Carbon-containing Groups.- 1.1. Alkyl Transfers.- 1.1.1. Alkyl Rearrangements.- 1.1.2. Stereochemistry of Nucleophilic Substitution Reactions at the sp3-hybridized Carbon Atom.- 1.1.3. Alkyl Migrations with Retention of Configuration at the sp3-carbon Atom.- 1.2. Vinylotropic Tautomerism.- 2. Silylotropic Tautomerism.- 3. Tautomeric Migrations of Phosphorus-containing Groups.- 3.1. PIV-Migrants.- 3.2. PIII-Migrants.- 3.3. PV-Migrants.- 4. Tautomeric Rearrangements of As-containing Groups.- 5. Tautomeric Rearrangements of Sulfur-containing Groups.- 5.1. SII-Migrants.- 5.2. SIII-Migrants.- 5.3. SIV-Migrants.- References.- 5. Dyotropic and Polytropic Tautomeric Systems.- 1. Scope and Definition.- 2. The Mechanism and Energetics of the Dyotropic Reactions.- 2.1. Concerted and Nonconcerted Dyotropic Rearrangements.- 2.2. Multigraphs of Dyotropic and Polytropic Systems.- 2.3. Quantum Mechanical Studies on the Mechanism of Dyotropic Reactions.- References.- 6. Dissociative and Photochemical Mechanisms of Intramolecular Tautomerism.- 1. Heterolytic Dissociative Mechanism.- 2. Homolytic Dissociative Mechanism.- 3. Ion-Radical Mechanism.- 4. Photo-Initiated Carbonotropic Rearrangements.- 4.1. Photochromic Transformations.- 4.2. Photoacylotropic Rearrangements.- 4.3. Photoacylotropic Compounds as Abiotic Photochemical Solar Energy Storage Systems.- 4.4. Photoinduced Aryl Rearrangements.- 4.5 Photo-Induced Rearrangements of the Csp3-centered Groups.- References.