Microcalorimetry as a tool in mechanistic studies of organic reactions

Abstract

Isothermal microcalorimetry is a powerful tool in studies of organic reactions in solution. Both reaction kinetics and thermodynamic parameters at a single temperature are conveniently derived by this technique. Some applications of batch microcalorimetry in reaction mechanistic studies are reviewed. These include kinetic and thermodynamic studies of aromatization reactions of biologically interesting oxides, hydrates of aromatic hydrocarbons and studies of complex reactions and equilibria. Copyright © 2002 John Wiley & Sons, Ltd.

Borderline between E1cB and E2 Mechanisms. Chlorine Isotope Effects in Base-Promoted Elimination Reactions

“…We find it most likely that these large isotope effects, combined with the large hydrogen isotope effects, are strongly indicative of a synchronous E2 mechanism. Consistently, there are large element effects: k Br / k Cl = 10 with methoxide ion and k Br / k Cl = 5 with TEA . The situation resembles the concerted S N 2 reaction in which there is a synergism between an efficient entering nucleophile and an efficient departing leaving group. , …”

“…However, theoretical calculations have shown that a partial bond breaking to the putative leaving group (L) occurs in the transition state of hydron-abstracting reactions and that periplanar positioning between the base and L is preferred . This assistance to hydron removal by hyperconjugative interaction from the electron-withdrawing group L implies some resemblance between E2 and E1cB transition-state structures. ,,,− …”

Kinetic and Thermodynamic Stability of Naphthalene Oxide and Related Compounds. A Comparative Microcalorimetric and Computational (DFT) Study

“…Microcalorimetric Procedure. This technique has the advantage that both kinetic data and reaction heats are obtained from the same kinetic experiment . The reactions were run in parallel in the two channels, both composed of a sample compartment and a reference compartment.…”

“…The microcalorimeter was statically calibrated after a kinetic experiment using the reaction solutions. No correction for the cooling constant parameter ( κ ) of the instrument was necessary for calculation of the rate constants of the reaction heat decay . Very good first-order rate constants ( k obs ) were measured.…”

Three important calorimetric applications of a classic thermodynamic equation

“…This technique has been extensively developed to characterise complex reactions, 30 probe long term stabilities of, for example, pharmaceutically important compounds, 31 determine orders, rate constants and enthalpies of reaction, 32 screen catalysts 33 and examine mechanisms of organic reactions. 34,35…”