XIV Contents 5 Solvent Effects on the Rates of Homogeneous Chemical Reactions...... 147 1 General Remarks. 5.2 Gas-Phase Reactivities 155 5.3 Qualitative Theory of Solvent Effects on Reaction Rates.. 162 531 The Hughes-Ingold Rules 163 5.3.2 Solvent Effects on Dipolar Transition State Reactions. 533 Solvent Effeets on Is olar Transition State Reactions. 5.3.4 Solvent Effects on Free-Radical Transition State Reactions 199 535 Limitations of the Hughes-Ingold Rules 215 5.4 Quantitative Theories of Solvent Effects on Reaction Rates 218 541 General Remarks 218 54) Reactions between Neutral.Apolar Molecules 219 543 Reactions between ner ral Dinolar molecule 225 utral Molecules and Ion 233 545 234 5.5 ecific Solvation Effects on Reaction Rates 237 551 eof Specific Anion Solvation on the Rates of SN and other 238 552 and Dipolar Aprotic Solve 243 5.5.3 polar R of Solvent-Tran Aprotic Solvents ation or 556 Reactions. ven 5.5.7 on the Effects on Mechanisms and Stereochemistry of Organic 273 5.5.8 of Micelar n and Mechanisms. Reaction Rates 292 Liquid Crystals as Reaction Media..................... Solvent Ca age Effects. 5.5.11 External Pressure and Solvent Effects on Reaction Rates............. 5.5.12 00 Solvent Isotope Effects.................. 5.5.13 Reactions in Biphasic Solvent Systems and in Neoteric Solvents....... 317 6 Solvent Effects on the Absorption Spectra of Organic Compounds...... 329 61 62 on UV/Vis S nic Co pectra.. 8 mp 330 f Sol s on UV/Vis 340 vent ects on UV/Vi Ab sorption Spectra .............. 6.25 Efects on ORD and CD Spectra 6.3 Solvent cts on 6.4 frared Spectra fects on Electron Spin Resonance Spectra.................. 5 Solvent E¤ects on the Rates of Homogeneous Chemical Reactions...... 147 5.1 General Remarks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 5.2 Gas-Phase Reactivities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 5.3 Qualitative Theory of Solvent E¤ects on Reaction Rates. . . . . . . . . . . . . . 162 5.3.1 The Hughes–Ingold Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 5.3.2 Solvent E¤ects on Dipolar Transition State Reactions . . . . . . . . . . . . . . . . 173 5.3.3 Solvent E¤ects on Isopolar Transition State Reactions. . . . . . . . . . . . . . . . 187 5.3.4 Solvent E¤ects on Free-Radical Transition State Reactions . . . . . . . . . . . 199 5.3.5 Limitations of the Hughes–Ingold Rules. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215 5.4 Quantitative Theories of Solvent E¤ects on Reaction Rates. . . . . . . . . . . 218 5.4.1 General Remarks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218 5.4.2 Reactions between Neutral, Apolar Molecules . . . . . . . . . . . . . . . . . . . . . . . 219 5.4.3 Reactions between Neutral, Dipolar Molecules. . . . . . . . . . . . . . . . . . . . . . . 225 5.4.4 Reactions between Neutral Molecules and Ions . . . . . . . . . . . . . . . . . . . . . . 233 5.4.5 Reactions between Ions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234 5.5 Specific Solvation E¤ects on Reaction Rates . . . . . . . . . . . . . . . . . . . . . . . . . 237 5.5.1 Influence of Specific Anion Solvation on the Rates of SN and other Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238 5.5.2 Protic and Dipolar Aprotic Solvent E¤ects on the Rates of SN Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243 5.5.3 Quantitative Separation of Protic and Dipolar Aprotic Solvent E¤ects for Reaction Rates by Means of Solvent-Transfer Activity Coe‰cients 254 5.5.4 Acceleration of Base-Catalysed Reactions in Dipolar Aprotic Solvents 259 5.5.5 Influence of Specific Cation Solvation on Rates of SN Reactions . . . . . . 262 5.5.6 Solvent Influence on the Reactivity of Ambident Anions. . . . . . . . . . . . . . 269 5.5.7 Solvent E¤ects on Mechanisms and Stereochemistry of Organic Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273 5.5.8 Influence of Micellar and Solvophobic Interactions on Reaction Rates and Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292 5.5.9 Liquid Crystals as Reaction Media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298 5.5.10 Solvent Cage E¤ects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303 5.5.11 External Pressure and Solvent E¤ects on Reaction Rates . . . . . . . . . . . . . 308 5.5.12 Solvent Isotope E¤ects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315 5.5.13 Reactions in Biphasic Solvent Systems and in Neoteric Solvents. . . . . . . 317 6 Solvent E¤ects on the Absorption Spectra of Organic Compounds ...... 329 6.1 General Remarks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329 6.2 Solvent E¤ects on UV/Vis Spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330 6.2.1 Solvatochromic Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330 6.2.2 Theory of Solvent E¤ects on UV/Vis Absorption Spectra. . . . . . . . . . . . . 340 6.2.3 Specific Solvent E¤ects on UV/Vis Absorption Spectra . . . . . . . . . . . . . . . 348 6.2.4 Solvent E¤ects on Fluorescence Spectra. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 352 6.2.5 Solvent E¤ects on ORD and CD Spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359 6.3 Solvent E¤ects on Infrared Spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363 6.4 Solvent E¤ects on Electron Spin Resonance Spectra . . . . . . . . . . . . . . . . . . 369 XIV Contents