Rotational Spectrum and Conformational Composition of Cyanoacetaldehyde, a Compound of Potential Prebiotic and Astrochemical Interest

Abstract

The rotational spectrum of cyanoacetaldehyde (NCCH(2)CHO) has been investigated in the 19.5-80.5 and 150-500 GHz spectral regions. It is found that cyanoacetaldehyde is strongly preferred over its tautomer cyanovinylalcohol (NCCH═CHOH) in the gas phase. The spectra of two rotameric forms of cyanoacetaldehyde produced by rotation about the central C-C bond have been assigned. The C-C-C-O dihedral angle has an unusual value of 151(3)° from the synperiplanar (0°) position in one of the conformers denoted I, while this dihedral angle is exactly synperiplanar in the second rotamer called II, which therefore has C(s) symmetry. Conformer I is found to be preferred over II by 2.9(8) kJ/mol from relative intensity measurements. A double minimum potential for rotation about the central C-C bond with a small barrier maximum at the exact antiperiplanar (180°) position leads to Coriolis perturbations in the rotational spectrum of conformer I. Selected transitions of I were fitted to a Hamiltonian allowing for this sort of interaction, and the separation between the two lowest vibrational states was determined to be 58794(14) MHz [1.96112(5) cm(-1)]. Attempts to include additional transitions in the fits using this Hamiltonian failed, and it is concluded that it lacks interaction terms to account satisfactorily for all the observed transitions. The situation was different for II. More than 2000 transitions were assigned and fitted to the usual Watson Hamiltonian, which allowed very accurate values to be determined not only for the rotational constants, but for many centrifugal distortion constants as well. Two vibrationally excited states were also assigned for this form. Theoretical calculations were performed at the B3LYP, MP2, and CCSD levels of theory using large basis sets to augment the experimental work. The predictions of these calculations turned out to be in good agreement with most experimental results.

Millimeter and submillimeter wave spectroscopy of propanal

“…The omission of F ac may influence the ability to determine higher order parameters or affect their values. Complications by describing molecules with two stable degenerate forms and necessary treatment of Coriolis interactions occurred already before [26,27]. For conformer I of cyanoacetaldehyde only transitions up to K a = 2 for 0 + and up to K a = 8 for 0 − -state are employed in the fit and moreover transitions with J equal to 30, 31, and 32 needed to be excluded [26].…”

“…Complications by describing molecules with two stable degenerate forms and necessary treatment of Coriolis interactions occurred already before [26,27]. For conformer I of cyanoacetaldehyde only transitions up to K a = 2 for 0 + and up to K a = 8 for 0 − -state are employed in the fit and moreover transitions with J equal to 30, 31, and 32 needed to be excluded [26]. For synclinal mercaptoacetonitrile, the standard deviation is four times larger than the expected experimental uncertainty and again special kinds of transitions were excluded, regarding large deviations between experimental and calculated frequencies [27].…”

Formation of interstellar cyanoacetamide: a rotational and computational study

“…The rotational spectrum and conformational composition of cyanoacetaldehyde has previously been reported by Møllendal et al (2012). Its existence in interstellar space and in planetary atmospheres is quite likely because of the facile formation of cyanoacetylene in liquid water (Ferris et al 1968), presumably formed in a catalytic process (Horn et al 2008).…”

Fate of the Gas-Phase Reaction Between Oxirane and the CN Radical in Interstellar Conditions

“…Considering the title reaction as potential formation route of the C 3 H 3 NO isomers, the only species belonging to this family that can be produced are cyanoacetaldehyde and, quite unlikely from the kinetic point of view, oxazole. Although the rotational spectrum of cyanoacetaldehyde has been studied in the laboratory (Møllendal et al, 2012), this species has never been searched for in the ISM and its abundance in any astronomical source is unknown. As far as oxazole is concerned, its formationwhich proceed through a ring expansion mechanisminvolves a TS that at the current level of theory is above the energy of the reactants.…”