title: Microwave spectrum, structure, and quantum chemical studies of a compound of potential astrochemical and astrobiological interest: Z-3-amino-2-propenenitrile.
abstract: Z-3-Amino-2-propenenitrile, H2NCH=CHCN, a compound of astrochemical and astrobiological interest, has been studied by Stark and Fourier transform microwave spectroscopy along with eight of its isotopologues; the synthesis of five of these are reported. The spectra of the ground vibrational state and of three vibrationally excited states belonging to the two lowest normal modes were assigned for the parent species, whereas the ground states were assigned for the isotopologues. The frequency of the lowest in-plane bending fundamental vibration was determined to be 152(20) cm(-1) and the frequency of the lowest out-of-plane fundamental mode was found to be 176(20) cm(-1) by relative intensity measurements. A delicate problem is whether this compound is planar or slightly nonplanar. It was found that the rotational constants of the nine species cannot be used to conclude definitely whether the molecule is planar or not. The experimental dipole moment is mu(a) = 16.45(12), mu(b) = 2.86(6), mu(c) = 0 (assumed), and mu(tot.) = 16.70(12) x 10(-30) C m [5.01(4) D]. The quadrupole coupling constants of the two nitrogen nuclei are chi(aa) = -1.4917(21) and chi(cc) = 1.5644(24) MHz for the nitrogen atom of the cyano group and chi(aa) = 1.7262(18) and chi(cc) = -4.0591(17) MHz for the nitrogen atom of the amino group. Extensive quantum-chemical calculations have been performed, and the results obtained from these calculations have been compared with the experimental values. The equilibrium structures of vinylamine, vinyl cyanide, and Z-3-amino-2-propenenitrile have been calculated. These calculations have established that the equilibrium structure of the title compound is definitely nonplanar. However, the MP2/VQZ energy difference between the planar and nonplanar forms is small, only -423 J/mol. Z-Amino-2-propenenitrile and E-3-amino-2-propenenitrile are formed simply by mixing ammonia and cyanoacetylene at room temperature. A plausible reaction path has been modeled. G3 calculations indicate that the enthalpy (298.15 K, 1 atm) of the transition state is about 130 kJ/mol higher than the sum of the enthalpies of the reactants ammonia and cyanoacetylene. This energy difference is comparatively high, which indicates that both E- and Z-3-aminopropenenitrile are not likely to be formed in the gas phase in cold interstellar clouds via a collision between ammonia and cyanoacetylene. An alternative reaction between protonated cyanoacetylene (H-C[triple bond]C-C[triple bond]NH+) and ammonia is predicted to have a much lower activation energy than the reaction between the neutral molecules. Although protonated E- and Z-3-aminopropenenitrile in principle may be formed this way, it is more likely that a collision between NH3 and H-C[triple bond]C-C[triple bond]NH+ leads to NH4+ and H-C[triple bond]C-C[triple bond]N.
authors.affiliation: Department of Chemistry, University of Oslo, Post Office Box 1033 Blindern, NO-0315 Oslo, Norway, UMR CNRS 6226.
authors.forename: Eva
authors.initials: E
authors.lastname: Askeland
authors.forename: Harald
authors.initials: H
authors.lastname: Møllendal
authors.forename: Einar
authors.initials: E
authors.lastname: Uggerud
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Guillemin
authors.forename: Juan-Ramon
authors.initials: JR
authors.lastname: Aviles Moreno
authors.forename: Jean
authors.initials: J
authors.lastname: Demaison
authors.forename: Thérèse R
authors.initials: TR
authors.lastname: Huet
mesh_terms: D000114:Acetylene / Q000031:analogs & derivatives / Q000737:chemistry; D002627:Chemistry, Physical / Q000379:methods; D018559:Exobiology / Q000379:methods; D005118:Extraterrestrial Environment; D005583:Fourier Analysis; D008872:Microwaves; D008956:Models, Chemical; D015233:Models, Statistical; D008968:Molecular Conformation; D009570:Nitriles / Q000737:chemistry*; D009584:Nitrogen / Q000737:chemistry; D011522:Protons; D011789:Quantum Theory; D013053:Spectrophotometry
chemical_list: C516496:3-amino-2-propenenitrile; D009570:Nitriles; D011522:Protons; C513097:cyanoacetylene; D009584:Nitrogen; D000114:Acetylene