Molecular properties of 2-azidoethanol and 2-chloroethyl azide. A theoretical study

Abstract

Ab initio calculations for 2-azidoethanol (N 3CH 2CH 2OH) and 2-chloroethyl azide (N 3CH 2CH 2Cl) and for the respective singly ionized structures are reported. Ionization energies based on Koopmans' theorem are in good agreement with UV photoelectron spectral measurements. However, adiabatic energy differences between the singly ionized structures and the neutral molecules ( ΔE values) are very sensitive to the consideration of electronic correlation effects. The conformational equilibrium of 2-azidoethanol and 2-chloroethyl azide is very dependent on the quality of the basis set and on the consideration of electronic correlation effects. For 2-azidoethanol the energy difference between the anti and gauche conformers, δ a − g = E a − E g , is 4.8 kJ mol −1 at the HF/6-31G level and 0.20 kJ mol −1 at MP2/6-31G. Further calculations using the previous geometry at the MP2/6-31G ∗∗ level gives −0.18 kJ mol −1. These results indicate that the gauche conformer is the most stable and also suggest the possibility of frequent interconversions between these two conformers of 2-azidoethanol in the gas phase. For 2-chloroethyl azide the anti-gauche conformational equilibrium is significantly modified when electronic correlation effects are introduced into the calculations: δ a − g is 0.652 kJ mol −1 at the HF/631G and −0.395 kJ mol −1 at the MP2/6-31G theoretical levels.