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 ZZ- type 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.
Highlights
Aminoacrylonitrile 1 (3-amino-2-propenenitrile) is a kinetically stable enamine of great astrochemical interest for its possible presence in the interstellar medium, the comets, and the atmospheres of planets, including the primitive Earth
The most stable aminoacrylonitrile dimers can be classified according to the nature of the interacting monomers as EE, EZ- and ZZ-type
The primary factor controlling the relative stability of these dimers is the intrinsic stability of the two monomers intervening in the complex
Summary
Aminoacrylonitrile 1 (3-amino-2-propenenitrile) is a kinetically stable enamine of great astrochemical interest for its possible presence in the interstellar medium, the comets, and the atmospheres of planets, including the primitive Earth. The formation of this compound in the aforementioned media is likely associated with the reaction of cyanoacetylene 2 (HC≡C-C≡N) and ammonia. The Z/E ratio in the reaction mixture is about 1 (unity) but rises to about 20 after distillation in vacuo.[13]
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