A theoretical study on the dimers of aminoacrylonitrile (3-amino-2-propenenitrile), a compound of astrochemical interest

Abstract

The structure, bonding, and relative stability of the dimers of aminoacrylonitrile were investigated through the use of high level density functional theory (DFT) calculations. Geometries and harmonic vibrational frequencies were obtained at the B3LYP/6-311+G(d,p) level. Final energies were estimated by means of B3LYP/6-311+G(3df,2pd) single point calculations. The aminoacrylonitrile dimers can be classified attending to the nature of the interacting monomers as EE-, EZ- or ZZ-types. The primary factor controlling the relative stability of these dimers is the intrinsic stability of the two monomers combining in the complex. Since the Z monomer is predicted to be ca. 8 kJ mol-1 more stable than the E monomer, the ZZtype dimers are more stable than the EZ ones, and these are more stable than the EE ones. Irrespective of the composition of the dimer, the most stable complexes correspond to those in which the HB acceptor is the cyano group. The global minimum, ZZ1, benefits not only from the enhanced stability of the Z monomer but also from non-negligible cooperative effects. The estimated dimerization enthalpy for aminoacrylonitrile (55.8 kJ mol-1) is only slightly smaller than those of carboxylic acids, such as formic, acetic or trifluoroacetic acid. Hence, the aminoacrylonitrile vapors should contain a significant amount of dimers. ©ARKAT.