Low frequency vibrational spectrum and conformational analysis of allylamine

Abstract

The Raman spectra of gaseous, liquid and solid allylamine and allylamine- N- d 2 as well as the i.r. spectra of these gases and solids have been recorded from 3500 to 50 cm −1 with special emphasis on the low frequency spectral region. The fundamental of the vinyl asymmetric torsion of the cis—trans conformer (vinyl moiety cis to the nitrogen atom and the lone electron pair on the nitrogen atom trans to the methylene hydrogens) of CH 2CHCH 2NH 2 was observed at 170.3 cm −1 with two accompanying hot bands and the corresponding torsion of the gauche—trans conformer has been observed at 110.4 cm −1, again with two accompanying hot bands, in the i.r. spectrum of the gas. From these data the potential function for internal rotation of the asymmetric vinyl top has been determined and the following potential constants have been evaluated: V 2 = 462 ± 29, V 3 = 954 ± 12, V 4 = 57 ± 8 and V 6 = −58 ± 5cm −1. It has been determined that the cis—trans conformer is the most stable form at ambient temperature in the gas phase and the enthalpy difference between the cis—trans and the gauche-trans conformers is 340 ± 20cm −1 (972 ± 57 cal/mol) for the vapor. This value is consistent with a temperature study of the i.r. spectrum of the vapor. Additionally the vinyl asymmetric torsion for one of the gauche—gauche conformers was observed at 122.9cm −1 with tentative assignments given for this torsional mode for the other two conformers. The fundamental amino torsions for four of the conformers have been observed at 275,252,242 and 228 cm −1 for CH 2CHCH 2NH 2 which shift with deuteration of the amino group to 209, 197, 185 and 171 cm −1; tentative assignments of these bands to the individual conformers are also proposed. The vibrational spectra of allylamine and allylamine- N- d 2 have been reinvestigated in view of the additional Raman gas phase data, and normal coordinate calculations have been carried out. These results are discussed and compared with the previous studies.