Activation volumes for cis-to-trans isomerisation reactions of azophenols: a clear mechanistic indicator?. Issue 2 (18th December 2017)

• Record Type: Journal Article
• Authors: Garcia-Amorós, Jaume; Stopa, Grzegorz; Stochel, Grazyna; van Eldik, Rudi; Martínez, Manuel; Velasco, Dolores
• Is Part Of: Physical chemistry chemical physics. Volume 20:Issue 2(2017)
• Page Start: 1286
• Page End: 1292
• Publication Date: 2017-12-18
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c7cp07349f
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : The thermal cis -to- trans isomerisation reaction of a series of hydroxy-substituted azo derivatives was studied kinetico-mechanistically as a function of temperature and pressure in order to investigate the possible role of the solvent in controlling the isomerisation mechanism, viz. inversion versus rotation. Abstract : The thermal cis -to- trans isomerisation reaction of a series of hydroxy-substituted azo derivatives was studied kinetico-mechanistically as a function of temperature and pressure in order to investigate the possible role of the solvent in controlling the isomerisation mechanism, viz. inversion versus rotation. The variation of the observed first order rate constants for kinetic runs carried out at different temperatures and pressures was used to determine the thermal activation parameters Δ H ‡ and Δ S ‡, and the pressure activation parameter Δ V ‡ . In addition, some experiments with deuterated species or solvents were also performed. The reported results could be interpreted as indicative of a changeover from an inversion mechanism for non-polar solvents to a rotational mechanism for polar solvents, capable of hydrogen bonding, for some of the systems studied. However, the operation of a rotational mechanism in all studied cases can account more consistently for the data observed.