The legacy of Gilbert Newton Lewis (1875-1946) pervades the lexicon of chemical bonding and reactivity. The power of his concept of donor-acceptor bonding is evident in the eponymous foundations of electron-pair acceptors (Lewis acids) and donors (Lewis bases). Lewis recognized that acids are not restricted to those substances that contain hydrogen (Bronsted acids), and helped overthrow the "modern cult of the proton". His discovery ushered in the use of Lewis acids as reagents and catalysts for organic reactions. However, in recent years, the recognition that Lewis bases can also serve in this capacity has grown enormously. Most importantly, it has become increasingly apparent that the behavior of Lewis bases as agents for promoting chemical reactions is not merely as an electronic complement of the cognate Lewis acids: in fact Lewis bases are capable of enhancing both the electrophilic and nucleophilic character of molecules to which they are bound. This diversity of behavior leads to a remarkable versatility for the catalysis of reactions by Lewis bases.

Lewis Base Catalysis in Organic Synthesis

Inorganic species in geologic fluids: Correlations among standard molal thermodynamic properties of aqueous ions and hydroxide complexes

The question of concerted or consecutive bond formation arises in all types of cycloaddition reactions. Stereochemical investigations and studies of regiospecificity as well as intensive kinetic investigations with regard to substituent and solvent effects, and the dependence of the reaction on temperature and pressure permit in many cases mechanistic conclusions concerning the Diels-Alder reaction. Efforts towards a theoretical interpretation, ab initio and semiempirical calculations, the application of frontier molecular orbital theory (FMO) as well as thermochemical measurements permit a description of the energy hypersurface of these [4+2]-cycloadditions. An attempt is made here to draw a line of distinction between the mechanistic alternatives—one-step reaction versus two-step reaction—considering all experimental and theoretical criteria.

Mechanistic Aspects of Diels‐Alder Reactions: A Critical Survey

Many biochemists would regard pressure as a physical parameter mainly of theoretical interest and of rather limited value in experimental biochemistry. The goal of this overview is to show that pressure is a powerful tool for the study of proteins and modulation of enzymatic activity.

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High Pressure Effects on Protein Structure and Function

2.3. Hydrocarbon Coordination 2475 2.4. σ Complexes of Alkanes and Arenes 2475 2.5. Principle of Microscopic Reversibility 2476 2.6. Kinetic Isotope Effects 2477 3. Shilov-type Chemistry 2478 3.1. C−H Activation by Pt(II) 2479 3.2. Mechanism of Multiple H/D Exchange 2480 3.3. H/D Exchanges1,2 Shift in Ethane 2481 3.4. Computational Studies of the Shilov System 2481 3.5. C−H Activation by Pt(IV) 2482 4. “Catalytica” System for Catalytic Methane Functionalization 2482

http://www.uwindsor.ca/users/j/jlichaa/reference.nsf/0/10ff8b04ff3a317885256d88005720f6/$FILE/cr-2005-105-2471%20tilset%20rev%20ch%20activ.pdf

C. D. Hubbard

Papers

Activation and Reaction Volumes in Solution. 3.