Ab initio studies of the conformers of 2-propene-1-imine

Abstract

Ab initio molecular orbital calculations employing both the minimal STO-3G and the split-valence 4-31G basis sets have been applied to the four planar conformers of 2-propene-1-imine. Initial calculations revealed that geometry optimizations were needed and partial geometry optimizations using the STO-3G method have been performed. Contrary to experiment, however, the STO-3G favors the wrong conformer (TS) as the lower energy structure. 4-31G calculations, on the other hand, are in reasonable agreement with the microwave study of the compound which predicts the TA conformer as the lower energy conformer with the TS conformer being 0.9 kcal mole −1 higher in energy. The most significant geometric variation in going from the TA to the TS conformer is an opening up of the CCN angle by about 5°. A comparison of the cis—trans rotamers of 1,3-butadiene, glyoxal and acrolein with 2-propene-1-imine is also made. The 4-31G calculations indicate that the TA — CA energy difference for 2-propene-1-imine is about 2 kcal mole −1 while the corresponding value for the TS — CS pair is 2.8 kcal mole −1.