Experimental studies suggest that methyl cyanide could be present in the interstellar medium (ISM). Azirine (C2H3N), a three-membered cyclic molecule, and its isomers are isomers of methyl cyanide, and thus could also be present in the ISM. Azirines are versatile substrates which are useful in synthesizing other heterocyclic rings. These molecules, however, are difficult to identify because of a current lack of experimental data. In this study ab initio quantum chemical methods were used to characterize the structures, relative energies, harmonic vibrational frequencies, and other physical properties of the 1H-azirine, 2H-azirine, and carbene cyclic isomers. Density Functional Theory (DFT) calculations were performed to optimize molecular geometries using the B3LYP and wB97-X functionals along with the 6-31+G* and cc-PVTZ basis sets. These were then further optimized; and harmonic vibrational frequencies, dipole moments, rotational constants, and proton affinities were calculated using the CCSD(T) method along with Dunning’s cc-pVXZ (X=T,Q, and 5) basis sets. We found that the 2H-azarine imine is the lowest in energy at all levels of theory employed. This is then followed by the C2H3N-carbene isomer, and lastly the 1H-azarine enamine isomer. All three cyclic isomers have a Cs symmetry equilibrium structure, and represent true minima on the singlet potential energy surface. Linear isomers and transition states for these molecules were also investigated for comparison. High-accuracy theoretical data calculated in this work can be compared to future experimentally obtained results, and, hopefully, be used to identify these molecules in the interstellar medium.

Characterization of azirine (C2H3N) and its isomers

255th National Meeting (2018)

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