THEORETICAL STUDY ON THE KINETICS AND MECHANISM OF THE REACTION OF CYCLOHEXYL ISOCYANIDE AND 1,1,1,5,5,5-HEXAFLUROPENTANE-2,4-DIONE USING DFT METHOD

Abstract

Kinetics and mechanism of the reaction between cyclohexyl isocyanide and 1,1,1,5,5,5-hexafluropentane-2,4-dione has been investigated by utilizing transition state theory and using B3LYP/6-31G* method. Based on previous experimental studies, two paths namely direct attack and conjugate addition have been proposed. Energy changes vs intrinsic reaction coordinate (IRC) along these paths have been studied both in the gas phase and considering nonspecific solvent effect under Onsager's model while all intermediate and possible transition states' geometries obtained and optimized. Small differences have been observed between gas phase and solution phase results. Taking advantage of the thermodynamic and kinetic calculated parameters, observed reaction rate constants and activation energies have been acquired. Computational results suggest that the conjugate addition path is totally unacceptable, while a new path has been proposed, which is both energetically and kinetically preferred to direct attack path. This new path undergoes the Michael addition along with a Cope–Claisen-type rearrangement. In this path, a new intermediate has been encountered for the first time, which contains a five-membered ring of four carbon atoms and one oxygen atom. NBO analysis has revealed that in such intermediate, oxygen lone pair has resonance with C – C π bond inside and C – N π bond outside of the ring leading to this species special stability. Molecular orbital calculations satisfy NBO findings.