COMPARED WITH the first five Jerusalem Symposia on Quantum Chemistry and Biochem­ istry, this sixth Symposium represents a step into a new and largely uncharted area: that of Chemical and Biochemical Reactivity. While the previous Symposia dealt principally with the 'static' data, describing molecules-even large ones-of chemical and biological in­ terest, the present Symposium attempts to deal with 'dynamic' phenomena and the factors which determine their course. The complexities of these systems and the ensuing theoreti­ cal (and experimental) difficulties are, obviously, much more pronounced. Nevertheless, we hope that the present volume of Proceedings makes a positive contribu­ tion to the very interesting field of Reactivity: the lively discussions which followed every paper seem to us a good indication that our hope is justified. As last year, we have includ­ ed in these Proceedings only those portions of the discussions which the participants themselves formulated in writing, and, of course, the replies given by the speakers, to whom we transmitted the written formulations. We must apologize to the participants in the Symposium for the long delay in publishing this volume. The October 1973 War, and, even more, its aftermath, made it impossible for us to produce the work by our scheduled date of April 1, 1974, as Israel's manpower, especially its technically skilled manpower, was not always free for its normal occupation.

Table of Contents:
Molecular Electrostatic Potentials — A Tool for Studying Biochemical Protonation Reactions.- Large-Scale CI Calculations for Studies of Energy Surfaces in Chemical Reactions.- Potential Energy Surfaces for Molecular Rearrangement.- Energy and Chemical Change — Energy Disposal and Energy Consumption in Elementary Chemical Reactions.- A Group Theory for Fluxional Systems — Permutation Symmetry and Carbonium Ions.- Localizability of Electrons and Chemical Reactivity.- Acid-Base Equilibrium of Conjugated Molecules in their First Excited States.- The Virial Partitioning Method.- On Least-Motion Analysis of Reaction Pathways.- Description of the Diradical State by the Direct Minimization Method.- Study of the Electronic Structure of Molecules — The Long Bottleneck.- SCF and CI Calculations of Bimolecular Reaction Surfaces.- Multiplicity Change During Thermal Dissociation.- The Oxirene Intermediate in the Ketene-Methylene + CO System.- Semi-Empirical CI Calculation of the Forbidden Reaction Path — The Least-Motion Dissociation of Ethylene to Form Methylenes.- Non-Empirical Calculations on Model Systems Containing Molecular Nitrogen or Carbon Monoxide.- Theoretical Studies on Donation and Back-Donation in Transition Metal Complexes.- Construction of Scattering Potentials for Electron- Molecule Encounters at Near-Thermal Energies.- Role of Partially Occupied d-Orbitals of Onium-Type Compounds in the Catalytic Activation of Molecular Oxygen.- Potential Curves for Proton Transfer Along Hydrogen Bonds.- Ab Initio Investigation of the Simultaneous Motion of Protons in the Hydrogen Bonds of the Cyclic Dimer of Formamide.- Semi-Empirical Calculations of the Activation Energies of Exchange Reactions R1. + R2H ? R2. + R1H (R = Alkyl).- A Theoretical Study on the Formationand Decomposition Mechanisms of Some Three-Membered Ring Systems.- Non-Planar Cyclopropylcarbinyl Cations — A Theoretical Treatment.- Subjacent Orbital Control and Superjacent Orbital Control.- Models for Homoaromatic Stability.- A Theoretical Study of the Reaction Mechanisms in Some Cyclo-Addition Reactions.- Ab Initio Calculations for Electrocyclic Reactions.- Influence of Correlation on the Calculation of the Energy Barrier for Nucleophilic Substitutions.- Charge Polarization—Induced Mixing of MO’s in Some Organic Reactions.- The Electrostatic Potential of the First Singlet and Triplet Excited States of Thymine.- Nucleophilic and Electrophilic Substitution Reactions of Purines.- Reactivity Maps for Flavins.- Study of the Influence of Attacking Ions and Dipoles on the Reactivity of Conjugated Systems.- The Geometry of the a Complex in an Electrophilic Aromatic Substitution Reaction.- CNDO/2 Calculations of Rotational Potential-Energy Functions, Internal Energies and Entropies of Some Methylbenzenes.- Electronic Aspects of the Bifunctional Catalysis of Glucose Mutarotation and Implications for Enzyme Catalysis.- The Structural Chemistry of Neural Transmission Systems.- Characterization of Drug Reactivity in Cholinergic Systems by Molecular Interaction Potentials.- Conformation and Reactivity of Two ?-Adrenergic Drugs: INPEA and Isoproterenol.- Quantum Chemical and Theoretical Techniques for the Understanding of the Action of Drugs Which Affect the Central Nervous System — Antipsychotics, Narcotics and Narcotic Antagonists.- Pharmacological Agent Design through Measurement of Glutathione Reactivity.- On Helix Formation in Polypeptides.- Concluding Remarks.