First order paralell and consecutive reaction mechanisms: isosbestic points criterium

A. E. CROCE

CANADIAN JOURNAL OF CHEMISTRY

NRC Research Press

Lugar: London, Ontario, Canada; Año: 2008

0008-4042

A criterium for reaction mechanisms selection derived from a condition for isosbestic points occurrence is presented. Analytical relationships involving the molar absorption coefficients of the species which participate in a mechanism of parallel first order reactions and the corresponding rate coefficients are also reported. A model system of four species which present overlapping absorption spectra may correspond to the reactant and products of a system of parallel or consecutive first order reactions. In the first case, under experimental conditions in which the absorbances are additive, the presence of an isosbestic point in the spectrum of the reaction mixture at a given wavelength leads to a time independent ratio of the degree of advancement of reaction variables. From this, relevant kinetic information may be extracted, namely, the ratio of the reaction rate coefficients. Moreover, the occurrence of isosbestic points allows to discard the second mechanism.  This conclusion is independent of the number of absorbing species. Model calculated examples show the application of the equations here derived. The resolution for the general case of mechanisms of N first order reactions is provided.