Transition state

About: Transition state is a research topic. Over the lifetime, 4978 publications have been published within this topic receiving 117965 citations. The topic is also known as: transition state of elementary reaction.

Experimental and Theoretical Examination of C−CN and C−H Bond Activations of Acetonitrile Using Zerovalent Nickel

Abstract: Experimental and density functional theory show that the reaction of acetonitrile with a zerovalent nickel bis(dialkylphosphino)ethane fragment (alkyl = methyl, isopropyl) proceeds via initial exothermic formation of an η2-nitrile complex. Three well-defined transition states have been found on the potential energy surface between the η2-nitrile complex and the activation products. The lowest energy transition state is an η3-acetonitrile complex, which connects the η2-nitrile to a higher energy η3-acetonitrile intermediate with an agostic C−H bond, while the other two lead to cleavage of either the C−H or the C−CN bonds. Gas-phase calculations show C−CN bond activation to be endothermic, which contradicts the observation of thermal C−CN activation in THF. Therefore, the effect of solvent was taken into consideration by using the polarizable continuum model (PCM), whereupon the activation of the C−CN bond was found to be exothermic. Furthermore the C−CN bond activation was found to be favored exclusively o...

Chemical Kinetics and Reaction Dynamics

Abstract: Preface 1. Elementary 1.1. Rate of Reaction 1.2. Rate Constant 1.3. Order and Molecularity 1.4. Rate Equations 1.5. Half-life of a Reaction 1.6. Zero Order Reactions 1.7. First Order Reactions 1.8. Radioactive Decay as a First Order Phenomenon 1.9. Second Order Reactions 1.10. Third Order Reactions 1.11. Determination of Order of Reaction 1.12. Experimental Methods of Chemical Kinetics Exercises 2. Temperature Effect on Reaction Rate 2.1. Derivation of Arrhenius Equation 2.2. Experimental Determination of Energy of Activation and Arrhenius Factor 2.3. Potential Energy Surface 2.4. Significance of Energy of Activation Exercises 3. Complex Reactions 3.1. Reversible Reactions 3.2. Parallel Reactions 3.3. Consecutive Reactions 3.4. Steady-State Treatment 3.5. Chain Reactions Reactions Exercises 4. Theories of Reaction Rate 4.1. Equilibrium and Rate of Reaction 4.2. Partition Functions and Statistical Mechanics of Chemical Equilibrium 4.3. Partition Functions and Activated Complex 4.4. Collision Theory 4.5. Transition State Theory 4.6. Unimolecular Reactions and the Collision Theory 4.7. Kinetic and Thermodynamic Control 4.8. Hammond's Postulate 4.9. Probing of the Transition State Exercises 5. Kinetics of Some Special Reactions 5.1. Kinetics of Photochemical Reactions 5.2. Oscillatory Reactions 5.3. Kinetics of Polymerization 5.4. Kinetics of Solid State Reactions 5.5. Electron Transfer Reactions Exercises 6. Kinetics of Catalyzed Reactions 6.1. Catalysis 6.2. Theories of Catalysis 6.3. Characteristics of Catalytic Reactions 6.4. Mechanism of Catalysis 6.5. Activation Energies of Catalyzed Reactions 6.6. Acid Base Catalysis 6.7. Enzyme Catalysis 6.8. Influence of pH 6.9. Heterogeneous Catalysis 6.10. Micellar Catalysis 6.11. Phase Transfer Catalysis 6.12. Kinetics of Inhibition Exercises 7. Fast Reactions 7.1. Introduction 7.2. Flow Techniques 7.3. Relaxation Method 7.4. Shock Tubes 7.5. Flash Photolysis 7.6. ESR Spectroscopic Technique 7.7. NMR Spectroscopic Techniques Exercises 8. Reactions in Solutions 8.1. Introduction 8.2. Theory of Absolute Reaction Rate 8.3. Influence of Internal Pressure 8.4. Influence of Solvation 8.5. Reactions between Ions 8.6. Entropy Change 8.7. Influence of Ionic Strength (Salt Effect) 8.8. Secondary Salt Effect 8.9. Reactions between the Dipoles 8.10. Kinetic Isotope Effect 8.11. Solvent Isotope Effect 8.12. Hemmett Equation 8.13. Linear Free Energy Relationship 8.14. The Taft Equation 8.15. Compensation Effect Exercises 9. Reaction Dynamics 9.1. Molecular Reaction Dynamics 9.2. Microscopic-Macroscopic Relation 9.3. Reaction Rate and Rate Constant 9.4. Distribution of Velocities of Molecules 9.5. Rate of Reaction for Collisions with a Distribution of Relative Speeds 9.6. Collision Cross Sections 9.7. Activation Energy 9.8. Potential Energy Surface 9.9. Classical Trajectory Calculations 9.10. Potential Energy Surface and Classical Dynamics 9.11. Disposal of Excess Energy 9.12. Influence of Rotational Energy 9.13. Experimental Chemical Dynamics Suggested Readings Index

Transition State Spectroscopy of Bimolecular Chemical Reactions

Abstract: One of the fundamental goals of chemical physics has been to understand the nature of the potential energy surfaces on which chemical reactions occur. Much of this interest focuses on the transition state region: the region of the surface where chemical bonds are broken and reformed. The microscopic forces at play in the transition state region often control the observabk; properties of a reaction, including the reaction cross-section and the product angular and energy distributions. Indeed, the key issue in chemical reaction dynamics is to deduce the relationship between these asymptotic properties of a reaction and the detailed features of the transition state region, such as (in the case of a direct reaction) the saddle point location, barrier height, and bend potential near the saddle point. To resolve this issue successfully, one would like to measure the asymptotic properties and experimentally characterize the transition state region for a given reaction. During the last 20 years, most of the experimental emphasis has been on the former aspect; increasingly refined state-tostate scattering experiments have been developed in which final product distributions are measured as a function of wcll-defined reactant initial conditions (1). These experiments can provide a sensitive, although