Ab Initio and DFT Potential Energy Surfaces for Cyanuric Chloride Reactions

摘要

Ab initio and nonlocal density functional theory (DFT) calculations were performed to determine reaction mechanisms for formation of the six- membered ring C3N3Cl3 (cyanuric chloride) from the monomer, cyanogen chloride (ClCN). MP2 geometry optimizations followed by QCISD(T) energy refinements and corrections for zero-point energies for critical points on the potential energy surface were calculated using the 6-31G and 6-311 +Gbasis sets. DFT(B3LYP) geometry optimizations and zero-point corrections for critical points on the potential energy surface were calculated with the 6-31G, 6-311 +G, and cc-pVTZ basis sets. Two formation mechanisms of cyanuric chloride were investigated, the concerted triple association (3 ClCN to cyanuric chloride) and the step-wise association 3 ClCN to (Cl2C2N2 + ClCN) to cyanuric chloride. All calculations show that the lower energy path to formation of cyanuric chloride is the concerted triple association. MP2 and DFT intrinsic reaction coordinate (IRC) calculations starting from the transition state (TS) for concerted triple association reaction proceeding toward the isolated monomer resulted in the location of a local minimum, stable by as much as - 8.0 kcal/mol, that corresponds to a weakly bound cyclic (ClCN)3 cluster. The existence of this cluster on the reaction path for the concerted triple association could lower the entropic hindrance to this unusual association reaction mechanism.