Chapter One - Is the Single-Transition-State Model Appropriate for the Fundamental Reactions of Organic Chemistry? Experimental Methods and Data Treatment, Pertinent Reactions, and Complementary Computational Studies

The experimental recording of spectrophotometric data suitable for detailed kinetic analysis and reaction mechanism determination is covered early in the chapter with examples of experiments and subsequent data treatment on a variety of different chemical systems. Several new methods to distinguish between single-step and complex reaction mechanisms are described in detail. The fundamental organic reactions covered in more detail were limited to recent work on four general reaction types. These include (1) proton transfer reactions of nitroalkanes and related compounds, (2) S(N)2 reactions of CH3-X where X is the leaving group, (3) electrophilic aromatic substitution, and (4) hydride transfer reactions of NADH/NAD(+) model systems. In all cases possible, discussion of the experimental studies was complemented by computational studies on the same reaction systems. The experimental kinetic studies all involved short-lived intermediates and could only distinguish the complex mechanisms involved from the mechanism with a single transition state. Computational studies confirmed the complex nature of the mechanisms and provided structures for the likely intermediates in the experimental reactions. The energies of the noncovalently bonded intermediates were highly dependent on the computational method and therefore could not confirm the apparent Gibbs free energies of the transition states.