Synthesis and Characterization of (E)- and (Z)-3-Mercapto-2-propenenitrile. Microwave Spectrum of the Z-Isomer

Abstract

The kinetically unstable compound 3-mercapto-2-propenenitrile (HS-CH=CH-C[triple bond]N) has been prepared for the first time by flash vacuum pyrolysis at 800 degrees C of 3-(tert-butylthio)-2-propenenitrile with a yield of 77% and a Z:E ratio of 8:1. Several deuterium and 15N isotopologues were also prepared using isotopically enriched compounds. Quantum chemical calculations of the structural and conformational properties of the Z- and E-isomers were undertaken at the B3LYP/6-311++G(3df,2pd), MP2/6-311++G(3df,2pd), MP2/aug-cc-pVTZ, and G3 levels of theory. These methods all predict that the Z- and the E-forms each have two "stable" planar rotameric forms with the H-S-C=C link of atoms in either a synperiplanar or an antiperiplanar conformation, with the synperiplanar form of the Z-isomer as the global minimum. The Z-isomer has been investigated by means of Stark-modulation microwave spectroscopy. Spectra attributable to the parent and three deuterium-substituted isotopologues of a single conformer were recorded and assigned. Additionally, the spectrum belonging to the first excited state of the lowest bending vibration was assigned. The ground-state rotational constants obtained by the least-squares analysis of these transitions were found to be in excellent agreement with the corresponding approximate equilibrium values generated by the MP2/aug-cc-pVTZ calculations. The preferred conformer of this molecule was found to have a synperiplanar arrangement of the H-S-C=C chain of atoms and a planar or nearly planar geometry, with a stabilizing intramolecular hydrogen bond formed between the H atom of the thiol group and pi-electron density associated with the C[triple bond]N triple bond. The possible astrochemical/astrobiological significance of this compound is discussed.

Microwave Spectrum and Intramolecular Hydrogen Bonding of 2-Isocyanoethanol (HOCH2CH2N≡C)

“…5 Examples of alkynes with intramolecular hydrogen bonds investigated by MW spectroscopy include propargyl alcohol (HOCH 2 CCH), 6 3-butyn-2-ol (H 3 CCH(OH)CCH), 7 3-butyn-1-ol (HOCH 2 CH 2 CCH), 8 − 12 4-pentyn-1-ol (HOCH 2 CH 2 CH 2 CCH), 13 propargyl thiol (HSCH 2 C CH), 14 3-butyne-1-thiol (HSCH 2 CH 2 CCH), 15 propargyl s e l e n o l ( H S e C H 2 C  C H ) , 1 6 3 -b u t y n e -1 -s e l e n o l (HSeCH 2 CH 2 CCH), 17 propargyl amine (H 2 NCH 2 C CH), 18 N-methylpropargyl amine (H 3 C(NH)CH 2 CCH), 19 and 1-amino-3-butyne (H 2 NCH 2 CH 2 CCH). 20 Similarly, intramolecular hydrogen bonding has been reported for a number of nitriles comprising hydroxyacetonitrile (HOCH 2 CN), 21 lactonitrile (H 3 CCH(OH)CN), 22 3-hydroxypropanenitrile (HOCH 2 CH 2 CN), 23 3-mercaptopropionitrile (HSCH 2 CH 2 CN), 24 Z-3-mercapto-2-propenenitrile (HSCHCHCN), 25 aminoacetonitrile (H 2 NCH 2 C N), 26,27 3-aminopropionitrile (H 2 NCH 2 CH 2 CN), 28 (Nmethylamino)ethanenitrile (H 3 C−NH−CH 2 CN), 29 2-aminopropionitrile (H 3 C(NH 2 )CHCN), 30 Z-3-amino-2-propenenitrile (H 2 NCHCHCN), 31 and 3-phosphinopropionitrile (H 2 PCH 2 CH 2 CN). 32 In contrast to these many investigations of internal hydrogen bonding with the π-electrons of the triple bonds in alkynes and nitriles, no gas-phase studies of this interaction have been reported for isonitriles (R−NC), the third functional group possessing a triple bond.…”

Organic synthesis applied to space sciences

“…Addition of H 2 S on cyanoacetylene only occurs in the presence of a base or under irradiation but only a diadduct, the sulfide, was obtained in our lab conditions even when using a huge excess of hydrogen sulfide. The 3-mercapto-2-propenenitrile 12 was prepared by flash vacuum thermolysis (FVT) of the t-butyl derivative [46]. The FVT is based on the vaporization in vacuo of a precursor in a short oven heated at a temperature ranging between 400 and 1200…”

“…The approaches reported above allowed recording the gas phase infrared spectra of these three compounds and their microwave spectra at room temperature [45,46,49,50]. The spectra have been given to observatories to help to their detection in the ISM, provided they are present.…”

Density Functional Theory Study of Cyanoetheneselenol: A Molecule of Astrobiological Interest

“…Heverley-Coulson and Boyd (2011) used high level computations like quadratic configuration interaction (QCISD) method with the cc-pVTZ basis set to study eight thio-and seleno-compounds as these are known to be of relevance when it comes to nucleic acids, nucleobases, some enzymes and substrates or even antioxidants. Cole et al (2007) studied cyanoethenethiol and reported that it is only kinetically stable at low temperatures and therefore the detection of the isomers would depend on their relative stabilities. An investigation of ethene selenol and ethene tellurol by Benidar et al (2009) revealed that both Z and E isomers of the former compound are unstable at room temperature.…”