Ab Initio and DFT Potential Energy Surfaces for Cyanuric Chloride Reactions

Abstract

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+G* basis 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. Good agreement is found for MP2 and DFT geometries and frequencies of cyanuric chloride and ClCN when compared with experimental values. Two formation mechanisms of cyanuric chloride were investigated, the concerted triple association (3 ClCN → cyanuric chloride) and the stepwise association (3ClCN → Cl2C2N2 + ClCN → 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 calculations starting from the transition state 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. The DFT/cc-pVTZ barrier to concerted triple association relative to isolated ClCN is 42.9 kcal/mol. The QCISD(T)//MP2/6-311+G* barrier to concerted triple association is 41.0 kcal/mol. The DFT/cc-pVTZ barrier to formation of the dimer (stepwise association reaction) is 63.4 kcal/mol while the QCISD(T)//MP2/6-311+G* barrier is 76.7 kcal/mol. The barrier to formation of cyanuric chloride relative to the (ClCN)3 minimum requires ∼46−49 kcal/mol, indicating that the concerted triple-association reaction via formation of the (ClCN)3 prereaction intermediate is the lower energy path to formation of cyanuric chloride. The temperature-corrected (T = 298 K) heats of reaction for formation of cyanuric chloride from ClCN are −63.4 and −61.2 kcal/mol for the B3LYP/cc-pVTZ and the QCISD(T)//MP2/6-311+G* predictions, respectively.

DFT and ab Initio Study of the Unimolecular Decomposition of the Lowest Singlet and Triplet States of Nitromethane

“…Numerous studies comparing these methods now exist in the literature (for example, see refs −5). Recent studies have shown that approximate functionals take into account most of the dynamical and static electron correlation effects, thus producing descriptions of molecular spectroscopic properties of comparable quality to more expensive correlated methods. − Relatively few comparative studies, however, have been performed to locate transition states and predict reaction paths . Such investigations are highly desirable in order to establish the limitations of DFT methods across wide regions of the molecular potential energy surface before subsequent dynamics simulations are performed.…”

“…[6][7][8][9] Relatively few comparative studies, however, have been performed to locate transition states and predict reaction paths. 10 Such investigations are highly desirable in order to establish the limitations of DFT methods across wide regions of the molecular potential energy surface before subsequent dynamics simulations are performed. Moreover, it is important to document the performance of DFT methods in describing a closed-shell system (singlet) and an open-shell counterpart (triplet) on an equal footing.…”

A Re‐Examination of the Reaction of 3,4‐Diamino[1,2,5]oxadiazole with Glyoxal

“…To understand why attempts to make 2 directly from 1 and glyoxal have been unsuccessful, reaction coordinate mapping was used to examine the reaction of both 1 and 4 with glyoxal . The results are shown in Figures and .…”

Anisotropic Repulsion Potentials for Cyanuric Chloride (C3N3Cl3) and Their Application to Modeling the Crystal Structures of Azaaromatic Chlorides

“…Generation and Fitting of the Atom-Atom Overlap Model. The calculations of the overlap and of the distributed multipoles 32 were carried out using a D 3h molecular structure, which was obtained by 3-21G SCF geometry optimization (and is almost identical to the 6-311+G MP2 optimized structure of Pai et al 36 ). A 6-31G* MP2 wave function of this structure was calculated using CADPAC.…”