Characterization of Rotational Isomerization Processes in Monorotor Molecules

Abstract

A theoretical approach, in which the potential functions representing rotational isomerization processes are expressed in terms of linear combinations of local potentials, is presented. Partitioning the torsional potential function allows the identification of specific contributions that are at the origin of the shape of the potential curves at different regions along the torsional variable. Key properties, such as barrier heights, are then expressed parametrically in terms of properties associated to the stable conformations. Simple analytic expressions are formulated in order to explore, quantitatively and qualitatively, the main characteristics of intermediate conformers connecting the reference isomers. This procedure is used to analyse ab initio results concerning the cis-trans isomerization reaction of three series of molecules: XY-NY, OXC-CXO, and XS-SX (X =H, F, or Cl; Y = O or S). We determine the relative stabilities of the different isomers and evaluate the associated potential barriers. It is shown that the mathematical procedure used to obtain potential functions is convenient enough to be applied to more complex isomerization reactions.