C-N barriers to internal rotations and vibrational analyses of carbamoylazide NNN-CONH₂

The internal rotations around two C-N bonds in carbamoylazide NNN-CONH ₂ were investigated by Density Functional B3LYP and ab initio second-order Möller Plesset MP2 calculations with the 6-311+G** basis set. Carbamoylazide was predicted at both levels to exist predominantly as the cis conformation (C=O and NNN moieties eclipse each other) with a cis-trans barrier of about 8 kcal/mol. The symmetric NH₂ torsional barrier was estimated to be about 20 kcal/mol by DFT and MP2 methods of calculations. The vibrational frequencies for the d₀ and d ₂ isotopic species of the molecule in the cis conformation were computed at the B3LYP/6-311+G** level and compared to experimental data. Normal coordinate calculations were then carried out and the potential energy distributions (PEDs) among the symmetry coordinates of the normal vibrational modes of the molecule were calculated. Complete vibrational assignments were provided on the basis of normal coordinate calculations, isotopic substitution and comparison with reported experimental data of the molecule.