Poster #P51



Uncovering the mechanism of photodenitrogenation reactions with NAMD simulations

Leticia A. Gomes, Steven A. Lopez



Photochemical reactions are examples of green chemistry used to synthesize strained molecules under mild conditions.[1,2] One example is the light-promoted denitrogenation of bicyclic azoalkanes, which can produce bicyclo[2.1.0]pentane with retained or inverted diastereoselectivity.[3,4] However, the mechanism behind these reactions has been disputed for over six decades. We employed multireference calculations and non-adiabatic molecular dynamics (NAMD) simulations on a series of diazabicyclo[2.2.1]heptenes to address longstanding mechanistic questions. Our simulations provide detailed information on their photophysical properties, reactivities, and mechanistic pathways. We used complete active space self-consistent field (CASSCF) calculations with an (8,9) active space and ANO-S-VDZP basis set. CASSCF energies were corrected with XMS-CASPT2(8,9)/ANO-S-VDZP. For the parent and two derivatives with methyl substituents the lowest excitations are nNN(σCN) → π* and range from 3.94 – 3.97 eV. We created 500 initial conditions using Wigner sampling for each molecule and implemented the fewest switches surface hopping NAMD simulations. We identify four pathways post S1/S0 intersections: the reversal to reactant, the inversion product exo-housane, the retention product endo-housane, and a diradical intermediate. Our analysis indicated that the diazoalkanes undergo asynchronous conical intersections, where one σCN bond breaks along the S1 and the other σCN breaks after hopping to the S0 (Figure 1).


Figure 1. σCN bonds plotted against each other for diazabicyclo[2.2.1]heptene. The bond lengths we calculated are depicted. The solid multicolor lines on each plot show the bond lengths over time, and the dots represent the S1/S0 surface hopping points for each trajectory.


  1. A. Albini, M. Fagnoni, Green Chemistry 2004, 6, 1-6.
  2. L. Buglioni, F. Raymenants, A. Slattery, S. D. A. Zondag, T. Noel, Chem Rev 2022, 122 (2), 2752-2906.
  3. C. Steel, The Journal of Physical Chemistry 1963, 67, 1779-1781.
  4. W. H. Roth, M. Martin, Tetrahedron Letters 1967, 8, 4695-4698.




 Leticia A. Gomes

  •   Northeastern University, Chemistry and Chemical Biology Department, Boston, USA