Molecular dynamics studies of the thermal decomposition of 2,3-diazabicyclo(2.2.1)hept-2-ene

Abstract

Microwave spectrum, dipole moment, and the conformation of 7oxabicyclo[4.1.0]hept3ene J. Chem. Phys. 68, 4027 (1978); 10.1063/1.436300 Lowfrequency vibrational spectra and conformations of bicyclo [3.2.0] hept6ene and 2oxabicyclo [3.2.0] hept6eneThe reaction dynamics of the thermal gas-phase decomposition of 2,3-diazabicyclo ͑2.2.1͒hept-2-ene-exo, exo-5,6-d 2 have been investigated using classical trajectory methods on a semiempirical potential-energy surface. The global potential is written as a superposition of different reaction channel potentials containing bond stretching, bending and torsional terms, connected by parametrized switching functions. Reaction channels for stepwise and concerted cleavage of the two C-N bonds of the reactant have both been considered in construction of the potential. The geometries of 2,3-diazabicyclo͑2.2.1͒hept-2-ene, the diazenyl biradical and of the transition state corresponding to breaking of the remaining C-N bond of diazenyl biradical have been determined at the second order Möller-Plesset perturbation theory ͑MP2/6-31G*͒ and at Hartree-Fock ͑HF/6-31G*͒ levels, respectively. The bond dissociation energies have been estimated using the available thermochemical data and previously reported results for bicyclo͑2.1.0͒pentane ͓J. Chem. Phys. 101, 3729 ͑1994͔͒. The equilibrium geometries predicted by the semiempirical potential for reactants and products, the barrier height for thermal nitrogen extrusion from 2,3-diazabicyclo͑2.2.1͒hept-2-ene and the fundamental vibrational frequencies are in good to excellent agreement with the measured or ab initio calculated values. Using a projection method of the instantaneous Cartesian velocities onto the normal mode vectors and classical trajectory calculations, the dissociation dynamics of 2,3-diazabicyclo͑2.2.1͒hept-2-ene-exo, exo-5,6-d 2 are investigated at several excitation energies in the range 60-175 kcal/mol. The results show the following: ͑1͒ The thermal reaction takes place with a preference for inversion of configuration in the reaction products, the exo-labeled bicyclo͑2.1.0͒ pentane being the major product. The exo/endo ratio of bicyclo͑2.1.0͒ pentane isomers is found to vary between 1.8 -2.2 for the energy range considered. ͑2͒ For random energization of the vibrational modes, the energy dependence of the rate coefficients can be described by a RRK expression. ͑3͒ The significant broadening and overlapping of the power spectral bands, together with the disappearance of characteristic features in the power spectra of the internal coordinates calculated at different energies, indicate high intramolecular vibrational redistribution rates and global statistical behavior. ͑4͒ The energy partitioning among products shows that the internal energy is preferentially distributed into the vibrational degrees of freedom in BCP, while N 2 is formed with small amounts of rotational and vibrational energies. Overall, the distribution of energy among the product degrees of freedom follows statistical predictions in the internal energy rang...

Machine Learning Analysis of Direct Dynamics Trajectory Outcomes for Thermal Deazetization of 2,3-Diazabicyclo[2.2.1]hept-2-ene

“…First, experiments showed that N 2 loss results in bicyclo products 3 and 4 with a nonstatistical preference for the exo product in a 4.7:1 ± 0.9 (exo:endo) ratio. , The statistical ratio would be 1:1 if the intervening 1,3-singlet diradical intermediate 2 were to undergo complete IVR prior to C–C bond formation. Second, several qualitative theories for the origin of selectivity have been proposed, beginning with Roth and Martin, , Allred and Smith, and culminating with Carpenter’s in-depth description that the nonstatistical exo:endo ratio results from a relatively low barrier (∼2 kcal/mol) for transition-state TS2 ( endo-TS2 and exo-TS2 , see Scheme ), which results in C–C bond formation without IVR. , More specifically, Carpenter’s description focused on the out-of-plane bending motion of the methylene (CH 2 ) bridge group that leads to the unexpected excess of exo product 3 , and this rationale was qualitatively supported by classical trajectory analyses and experiments in supercritical propane . Third, density functional theory (DFT) quasiclassical trajectories have not been reported.…”

Theoretical Studies of the Structure, Tautomerism, and Vibrational Spectra of 3-Amino-5-nitro-1,2,4-triazole

“…Insight in the dynamical aspects of the thermal decomposition of ANTA could be obtained by using molecular dynamics calculations if an accurate potential energy surface (PES) that describes the main geometric, spectroscopic, and thermochemical parameters of the reactant, products, and transition states were formulated. We have previously developed and used such PESs in molecular dynamics and Monte Carlo simulations of a number of cyclic nitro and diaza compounds, such as hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) , and 2,3-diazabicyclo[2.2.1]hept-2-ene. , In the present paper, we undertake the first step in the development of a reliable PES for ANTA by constructing a force field for the 2 H -ANTA molecule in the gas phase. This force field is based on the geometries and the scaled fundamental frequencies determined predicted by ab initio calculations at the MP2/6-311+G(d,p) level.…”

Viscosity-dependent diastereoselectivity and product selectivity in the photodenitrogenation of a spirocyclopropane-substituted, DBH-type azoalkane

“…The photodenitrogenation displays a viscosity effect, which demonstrates that a product bifurcation operates, with the 1 DZ diradical as common intermediate. The same frictional-power dependence of the diastereoselectivity (k inv /k ret ) and the product selectivity ([2]/ [3]) on viscosity (η Ϫα ), in which the α factor represents a measure of the free-volume requirement of the rearrangement process, 7,11 substantiates this conclusion.…”