Looking for heteroaromatic rings and related isomers as interstellar candidates

Abstract

Finding complex organic molecules in the interstellar medium (ISM) is a major concern for understanding the possible role of interstellar organic chemistry in the synthesis of prebiotic species. The present interdisciplinary report is a prospective study aimed at helping detection of heteroaromatic compounds or at least of some of their isomers in the ISM. The thermodynamic stabilities of the C(4)H(5)N, C(4)H(4)O, C(4)H(4)S families were calculated using density functional theory (DFT). It was found that pyrrole, furan and thiophene are unambiguously the most stable isomers at the 10-50 K temperatures of the ISM. Several of the less stable isomers were synthesized and flash vacuum thermolysis experiments were performed on these species. Although the detection of pyrrole in the pyrolysis of many compounds has been reported in the literature, we observed that none of its isomers led to pyrrole in these conditions, which suggests that other formation routes are to be considered. On the other hand, these three aromatic compounds present a very high stability, few % been decomposed at 1500 K by flash vacuum thermolysis; these experiments also show a great stability of crotonitrile that is the most stable compound that can be formed in these conditions. The rotational constants, dipole moments and IR frequencies of the low-lying isomers are given to encourage laboratory experiments on these prototype molecules.

The quest of chirality in the interstellar medium

“…Four out of seven of the aforementioned most stable isomers (noted Isomer Obs. ) have been identified in the ISM in agreement with MEP, but no molecule has been detected so far in the C 3 H 3 NO, C 4 H 4 O, and C 3 H 4 O 2 series; even furan was not detected despite its aromatic electronic structure (Lattelais et al 2010b).…”

Gas‐Phase Infrared Spectra of Three Compounds of Astrochemical Interest: Vinyl, Allenyl, and Propargyl Isocyanides

“…HNC has also been detected in the atmosphere of Titan,8 but attempts to detect the methyl and ethynyl derivatives have failed so far. Under standard laboratory conditions, isocyanides rearrange upon heating to give the thermodynamically more‐stable cyanide isomers;9, 10 however, some photochemical studies revealed the opposite rearrangement under irradiation 11. 12 New spectroscopic studies or improvements upon old studies of such simple isocyanides could provide useful tools for the detection of these species in the various areas of the universe where cyanide isomers have been detected, including the ISM, the atmosphere of Titan, and comets.…”

Density Functional Exploration of C4H3N Isomers

“…, furan18 , thiophene18 , acetonitrile19 , cyanoacetylene 20 , C 4 H 2 + isomers 21 , and C 2 HNS isomers22 .were tested on carbon chains including 1 as a quick and easy way to obtain fundamental vibrational frequencies25 , mostly with a view towards cost effective calculations of much larger molecules formed upon processing of astrochemical species. Electric field gradients and quadrupole coupling constants were calculated for 10 and compared to experimental values 26 in 1992.…”