Elucidation of Organic Reaction Mechanisms Using Nuclear Magnetic Resonance: A review

Nuclear magnetic resonance (NMR), a technique mainly used for structure determination, has also been extensively used for mechanism elucidation. The study of the different steps involved in a chemical reaction is of utmost importance since it permits the optimization of reaction conditions to improve the yield of a synthesis or to obtain one possible product over another one, for example. This review is organized into two sections. Firstly, the experimental issues concerning the applications of NMR to the elucidation of reaction mechanisms are revised: advantages, limitations and challenges are discussed. The different techniques used for overcoming the difficulties concerning NMR (such as low sensitivity, peak resolution, and mixing time) are described (including stop-flow, rapid-injection, liquid chromatography-NMR, dynamic nuclear polarization, and parahydrogen-induced polarization, among others). In the second section, experiments specifically designed for obtaining mechanistic information by means of different NMR techniques are summarized: kinetic experiments, detection of reaction intermediates, isotope labeling, variable-temperature experiments, and variable-pH experiments. The main objective of this work is to give an overview on the relevance of NMR as a very useful tool for elucidating organic reaction mechanisms.