Isopropyl Cyanide Research Articles

Astrochemical model to study the abundances of branched carbon-chain molecules in a hot molecular core with realistic binding energies

ABSTRACT Straight-chain (normal-propyl cyanide, $\rm {n-C_3H_7CN}$) and branched-chain (iso-propyl cyanide, $\rm {i-C_3H_7CN}$) alkyl cyanides are recently identified in the massive star-forming regions (Sgr B2(N) and Orion). These branched-chain molecules indicate that the key amino acids (side-chain structures) may also be present in a similar region. The process by which this branching could propagate towards the higher order (butyl cyanide, $\rm {C_4H_9CN}$) is an active field of research. Since the grain catalysis process could have formed a major portion of these species, considering a realistic set of binding energies are indeed essential. We employ quantum chemical calculations to estimate the binding energy of these species considering water as a substrate because water is the principal constituent of this interstellar ice. We find significantly lower binding energy values for these species than were previously used. It is noticed that the use of realistic binding energy values can significantly change the abundance of these species. The branching is more favourable for the higher order alkyl cyanides with the new binding energies. With the inclusion of our new binding energy values and one essential destruction reaction ($\rm {i-C_3H_7CN+H \rightarrow CH_3C(CH_3)CN + H_2}$, having an activation barrier of 947 K), abundances of $\rm {t-C_4H_9CN}$ dramatically increased.

Electro-optical, electronic and conformational transitions of interstellar alkyl molecules at different temperatures: An ab-initio study

In this paper, electronic structures of iso-propyl cyanide (i-C3H7CN), gauche-normal-propyl cyanide (g-n-C3H7CN) and anti-normal-propyl cyanide (a-n-C3H7CN) have been optimized using DFT/B3LYP/aug-cc-pVDZ and DFT/CAM-B3LYP/aug-cc-pVDZ methods in neutral and anionic states. Electro-optical properties, HOMO, LUMO and MEP surfaces have been computed in order to check the optical behaviour and chemical reactivity of these interstellar molecules. The a-n-C3H7CN molecule exhibits better electro-optical behaviour than g-n-C3H7CN and iso-C3H7CN molecules. Global reactivity descriptors, adiabatic and vertical electron affinities of these straight and branched alkyl molecules have been investigated. These molecules have negative electron affinities, which means that they emit energy in anionic form. The distribution of chemical bonding and electron lone pairs inside molecules has been discussed using ELF map. Infrared and absorption spectra of these interstellar molecules have been studied in the light of experimental data. Further, formations of g-n-C3H7CN from i-C3H7CN, a-n-C3H7CN from i-C3H7CN and a-n-C3H7CN from g-n-C3H7CN have been examined using transition state at 10 ​K, 298.15 ​K and 500 ​K temperatures. Mechanism of formation of g-n-C3H7CN and a-n-C3H7CN from i-C3H7CN at 10 ​K, 298.15 ​K and 500 ​K temperatures along with their physico-chemical properties have been elucidated.

Quantum chemical study on the formation of isopropyl cyanide and its linear isomer in the interstellar medium

AbstractThe formation mechanism of linear and isopropyl cyanide (hereafter n-PrCN and i-PrCN, respectively) in the interstellar medium (ISM) has been proposed from the reaction between some previously detected small cyanides/cyanide radicals and hydrocarbons/hydrocarbon radicals. n-PrCN and i-PrCN are nitriles therefore, they can be precursors of amino acids via Strecker synthesis. The chemistry of i-PrCN is especially important since it is the first and only branched molecule in ISM, hence, it could be a precursor of branched amino acids such as leucine, isoleucine, etc. Therefore, both n-PrCN and i-PrCN have significant astrobiological importance. To study the formation of n-PrCN and i-PrCN in ISM, quantum chemical calculations have been performed using density functional theory at the MP2/6-311++G(2d,p)//M062X/6-311+G(2d,p) level. All the proposed reactions have been studied in the gas phase and the interstellar water ice. It is found that reactions of small cyanide with hydrocarbon radicals result in the formation of either large cyanide radicals or ethyl and vinyl cyanide, both of which are very important prebiotic interstellar species. They subsequently react with the radicals CH2 and CH3 to yield n-PrCN and i-PrCN. The proposed reactions are efficient in the hot cores of SgrB2 (N) (where both n-PrCN and i-PrCN were detected) due to either being barrierless or due to the presence of a permeable entrance barrier. However, the formation of n-PrCN and i-PrCN from the ethyl and vinyl cyanide always has an entrance barrier impermeable in the dark cloud; therefore, our proposed pathways are inefficient in the deep regions of molecular clouds. It is also observed that ethyl and vinyl cyanide serve as direct precursors to n-PrCN and i-PrCN and their abundance in ISM is directly related to the abundance of both isomers of propyl cyanide in ISM. In all the cases, reactions in the ice have smaller barriers compared to their gas-phase counterparts.

Ab initio investigations of isopropyl cyanide reaction mechanisms and kinetics of formation on an icy grain model

AbstractIsopropyl-cyanide (iso-PrCN) was recently observed in Sagittarius B2 with an abundance higher than its straight-chain structure isomer (n-PrCN). Here we study theoretically by means of [UMP2(full)/aug-cc-pVTZ/Amber] a hybrid ab initio/molecular mechanics methodology, the routes leading to its formation on a formaldehyde doped water ice grain model of the interstellar medium. The reaction path and the energetics are calculated, the mechanism is found to be exothermic by ∼ 30 kcal/mol and the barrier is ∼ 70 kcal/mol. We use the CVT/ZCT semiclassical method to predict the kinetics of the reaction path starting from initially adsorbed HCN and CH2CHCH3 molecules colliding from the gas phase over the temperature range [100–500K].

A Comprehensive Rotational Study of Interstellar Iso-propyl Cyanide up to 480 GHz

Abstract A detailed analysis of the rotational spectra of the interstellar iso-propyl cyanide has been carried out up to 480 GHz using three different high-resolution spectroscopic techniques. Jet-cooled broadband chirped pulse Fourier transform microwave spectroscopy from 6 to 18 GHz allowed us to measure and analyze the ground-state rotational transitions of all singly substituted 13C and 15N isotopic species in their natural abundances. The monohydrate of iso-propyl cyanide, in which the water molecule bounds through a stronger O–H⋯N and weaker bifurcated (C–H)2⋯O hydrogen bonds in a C s configuration, has also been detected in the supersonic expansion. Stark-modulation spectroscopy in the microwave and millimeter wave range from 18 to 75 GHz allowed us to analyze the vibrational satellite pattern arising from pure rotational transitions in the low-lying vibrational excited states. Finally, assignments and measurements were extended through the millimeter and submillimeter wave region. The room temperature rotational spectra made possible the assignment and analysis of pure rotational transitions in 19 vibrationally excited states. Significant perturbations were found above 100 GHz in most of the observed excited states. Due to the complexity of the interactions and importance of this astrophysical region for future radioastronomical detection, both a graphical plot approach and a coupled fit have been used to assign and measure almost 10,000 new lines.

Rotational Spectroscopy of the Lowest Energy Conformer of 2-Cyanobutane.

Isopropyl cyanide was recently detected in space as the first branched alkyl compound. Its abundance with respect to n-propyl cyanide in the Galactic center source Sagittarius B2(N2) is about 0.4. Astrochemical model calculations suggest that for the heavier homologue butyl cyanide the branched isomers dominate over the unbranched n-butyl cyanide and that 2-cyanobutane is the most abundant isomer. We have studied the rotational spectrum of 2-cyanobutane between 2 and 24 GHz using Fourier transform microwave spectroscopy and between 36 and 402 GHz employing (sub)millimeter absorption spectroscopy. Transitions of the lowest energy conformer were identified easily. Its rotational spectrum is very rich, and the quantum numbers J and Ka reach values of 111 and 73, respectively. This wealth of data yielded rotational and centrifugal distortion parameters up to tenth order, diagonal and one off-diagonal 14N nuclear quadrupole coupling parameters, and one nuclear spin-rotation coupling parameter. We have also carried out quantum chemical calculations in part to facilitate the assignments. The molecule 2-cyanobutane was not found in the present ALMA data of Sagittarius B2(N2), but it may be found in the more sensitive data that have been completed very recently in the ALMA Cycle 4.

C5H9N isomers: pointers to possible branched chain interstellar molecules

The astronomical observation of isopropyl cyanide further stresses the link between the chemical composition of the ISM and molecular composition of the meteorites in which there is a dominance of branched chain amino acids as compared to the straight. However, observations of more branched chain molecules in ISM will firmly establish this link. In the light of this, we have considered C5H9N isomeric group in which the next higher member of the alkyl cyanide and other branched chain isomers belong. High-level quantum chemical calculations have been employed in estimating accurate energies of these isomers. From the results, the only isomer of the group that has been astronomically searched, n-butyl cyanide is not the most stable isomer and therefore, which might explain why its search could only yield upper limits of its column density without a successful detection. Rather, the two most stable isomers of the group are the branched chain isomers, tert-butylnitrile and isobutyl cyanide. Based on the rotational constants of these isomers, it is found that the expected intensity of tert-butylnitrile is the maximum among this isomeric group. Thus, this is proposed as the most probable candidate for astronomical observation. A simple LTE (Local thermodynamic equilibrium) modelling has also been carried out to check the possibility of detecting tert-butyl cyanide in the millimetre-wave region.

Simulations of branched carbon-chain chemistry in star-forming regions

AbstractThe detection of iso-propyl cyanide (i-C3H7CN) toward the Galactic Center hot-core source Sgr B2(N) (by Belloche et al. 2014) marked the first interstellar detection of an aliphatic molecule with a branched carbon-chain structure. Surprisingly, this branched form was found to have an almost equal abundance with its straight-chain homologue, normal-propyl cyanide (i:n = 0.40 ± 0.06). The detection of this first example of an interstellar molecule with a side-chain raises the question as to how prominent such structures may be in interstellar chemistry, and whether the large branched-to-straight chain ratio is maintained for even larger molecules.Here are presented recently published models that simulate the chemistry occurring in Sgr B2(N) using a chemical network that explicitly includes the straight-chain and branched forms of propyl cyanide (normal/iso) and butyl cyanide (normal/iso/sec/tert), as well as butane (n/i) and pentane (n/i/neo). Formation is assumed to occur on dust-grain surfaces, but a full complement of destruction mechanisms is included both on the grains and in the gas phase.The models suggest that branched structures become increasingly dominant as molecular sizes increase. In the case of butyl cyanide, the sec form is at least ∼2 times more abundant than the straight-chain normal form, and together the branched forms dominate normal-butyl cyanide by a factor of at least 3. The results for the larger alkanes suggest similarly large ratios of branched to straight-chain molecules. A key set of reactions in the surface/ice chemistry of interstellar nitriles is found to be the addition of the CN radical to unsaturated hydrocarbons, especially acetylene and ethene. The models also predict that the dominant, sec form of butyl cyanide reaches a peak abundance equal to that of n-propyl cyanide, albeit with a smaller emission radius. This makes s-C4H9CN a good candidate for detection. New ALMA observations to search for this molecule are ongoing.

Modeling the production of highly-complex molecules in star-forming regions

Molecules of increasing complexity are being observed toward star-forming regions, including the recently detected iso-propyl cyanide, the first interstellar branched carbon-chain molecule. Modeling the formation of new complex organics requires new grain-surface production mechanisms, as well as gas-phase and grain-surface destruction processes. The method for constructing networks for new molecules is discussed, as well as the results of recent models of branched carbon-chain molecule chemistry. The formation of both simple and complex organics in cold regions is also discussed. New, exact kinetics models indicate that complex molecules may be formed efficiently at very low temperatures, if CO is abundant on the grain surfaces.

Rotational spectroscopy, dipole moment and 14N nuclear hyperfine structure of iso-propyl cyanide

Rotational transitions of iso-propyl cyanide, (CH 3) 2CHCN, also known as iso-butyronitrile, were recorded using long-path absorption spectroscopy in selected regions between 37 and 600 GHz. Further measurements were carried out between 6 and 20 GHz employing Fourier transform microwave (FTMW) spectroscopy on a pulsed molecular supersonic jet. The observed transitions reach J and K a quantum numbers of 103 and 59, respectively, and yield accurate rotational constants as well as distortion parameters up to eighth order. The 14N nuclear hyperfine splitting was resolved in particular by FTMW spectroscopy yielding spin–rotation parameters as well as very accurate quadrupole coupling terms. In addition, Stark effect measurements were carried out in the microwave region to obtain a largely revised c-dipole moment component and to improve the a-component. The hyperfine coupling and dipole moment values are compared with values for related molecules both from experiment and from quantum chemical calculations.

Solvation Structures and Kinetics of Solvent Exchange Reactions of the Manganese(II) Ion in Six Nitriles As Studied by X-ray Diffraction, EXAFS, and NMR Techniques

The solution structure of the manganese(II) ion in acetonitrile (methyl cyanide, AN) has been determined by an X-ray diffraction technique: there are 6.0 ± 0.2 Mn−N bonds and the Mn−N bond length is 221 ± 1 pm. The solvation structures of the manganese(II) ion in propiononitrile (ethyl cyanide, PN), butyronitrile (propyl cyanide, BuN), isobutyronitrile (isopropyl cyanide, iBuN), valeronitrile (butyl cyanide, VN), and benzonitrile (phenyl cyanide, BzN) have been determined by extended X-ray absorption fine structure spectroscopy. The manganese(II) ion in all of these nitriles is six-coordinate octahedral with an Mn−N bond length of 221 ± 1 pm. The activation parameters for solvent exchange on the manganese(II) ion in the six nitriles have been determined by the nuclear magnetic resonance line broadening technique at various temperatures and pressures. The values of the rate constant ( , s-1), activation enthalpy (ΔH⧧, kJ mol-1), activation entropy (ΔS⧧, J mol-1 K-1), and activation volume (ΔV⧧, cm3 mol-1) for the nitrile exchange are 1.3 × 107, 28.6 ± 0.5, −13 ± 2, and −5.8 ± 0.2 in AN; 1.3 × 107, 29.6 ± 0.7, −10 ± 3, and −2.1 ± 0.4 in PN; 9.9 × 106, 31.3 ± 0.8, −6 ± 3, and −5.0 ± 0.8 in BuN; 1.1 × 107, 40.0 ± 0.4, 24 ± 1, and −2.5 ± 0.7 in iBuN; 9.3 × 106, 35.6 ± 0.7, 8 ± 3, and +0.6 ± 0.6 in VN; 1.2 × 107, 36.9 ± 0.8, 14 ± 3, and none in BzN, respectively. The values of ΔH⧧ and ΔS⧧ gradually increase with increasing bulkiness of the nitrile molecule, and the reaction mechanism is concluded to be less associative with increasing the bulkiness, because the Mn−N bond energy in the nitrile-solvated manganese(II) ion is similar in all nitriles. The change in the ΔV⧧ value is discussed in terms of the change in the size of the inner sphere.

Infrared spectra of gaseous organics: Application to the atmosphere of Titan—II. Infrared intensities and frequencies of C4 alkanenitriles and benzene

The infrared spectra of butanenitrile (n-propyl cyanide = n-PrCN), 2-methylpropanenitrile (isopropyl cyanide = i-PrCN), cyclopropanecarbonitrile (cyclopropyl cyanide = ΔCN) and benzene, in the gas phase, have been systematically studied in the 3000-250 cm−1 wavenumber region. For each of these compounds the most intense vibration bands have been determined. Their absolute intensities and the associated uncertainties have been estimated. These data were then used to derive upper limits of the mean mixing ratios of these compounds in Titan's atmosphere from a newly studied selection of IRIS i.r. spectra. The obtained upper limits are of the order of a few tenths of ppm for the studied nitriles and a few ppb for benzene.

ChemInform Abstract: MICROWAVE SPECTRUM, DIPOLE MOMENT AND STRUCTURE OF ISOPROPYL CYANIDE

Abstract The microwave spectrum of isopropyl cyanide, (CH 3 ) 2 CHCN, has been recorded from 26.5 to 40.0 GHz. Both A- and C-type transitions were observed. The R-branch assignments have been made for the ground and three different excited states. The following structural parameters were obtained: r (C-CN) = 1.501 A, ∠CCC = 113.8°, and an angle between the CCC plane and the CN bond of 53.8° with reasonable assumptions made for the structural parameters for the isopropyl moiety and the nitrile bond. The dipole moment components were determined to be μ a = 4.05±0.02, μ c = 1.4 ± 0.2 and μ t = 4.29 ±0.10 D. The dipole moment of t-butyl cyanide has been re-measured and found to have a value of4.34±0.04 D. From the relative intensities of the excited state lines, the two torsional modes were found to have frequencies of 200 ±20 and 249 ±10 cm −1 which gave a periodic barrier to internal rotation of 3.3 kcal mole −1 .

Microwave spectrum, dipole moment and structure of isopropyl cyanide

The microwave spectrum of isopropyl cyanide, (CH 3) 2CHCN, has been recorded from 26.5 to 40.0 GHz. Both A- and C-type transitions were observed. The R-branch assignments have been made for the ground and three different excited states. The following structural parameters were obtained: r(C-CN) = 1.501 Å, ∠CCC = 113.8°, and an angle between the CCC plane and the CN bond of 53.8° with reasonable assumptions made for the structural parameters for the isopropyl moiety and the nitrile bond. The dipole moment components were determined to be μ a = 4.05±0.02, μ c= 1.4 ± 0.2 and μ t = 4.29 ±0.10 D. The dipole moment of t-butyl cyanide has been re-measured and found to have a value of4.34±0.04 D. From the relative intensities of the excited state lines, the two torsional modes were found to have frequencies of 200 ±20 and 249 ±10 cm −1 which gave a periodic barrier to internal rotation of 3.3 kcal mole −1.

The vibrational spectra of 2-chloro, 2-bromo, 2-iodo and 2-cyanopropane

The infrared spectra of 2-chloro, 2-bromo, 2-iodo and 2-cyanopropane (the isopropyl halides and isopropyl cyanide) were recorded in the gaseous and liquid states in the region 5000–200 cm −1. Raman spectra of the liquids were obtained using He-Ne laser excitation and semiquantitative polarization data are reported. The vibrational spectra of these substances are very closely related and the spectra are interpreted in terms of C s , symmetry for all the molecules. A tentative assignment of the fundamental frequencies for each compound is proposed.

The Reaction between Hydrocarbon and Hydrogen Cyanide in Silent Electrical Discharge. III. The Reaction of Ethylene or Propylene with Hydrogen Cyanide

Abstract The present investigation was undertaken to find out whether or not the relative amounts of acrylonitrile obtained by the reaction between ethylene and hydrogen cyanide in a silent discharge are affected by the substances (Hg(CN)2, Cu, CuCN, Al, Zn and Fe) placed in a glass filter of the special discharge tube, and to examine the possibility of the direct introduction of a cyano radical into propylene by means of the silent discharge. The yield of acrylonitrile depended upon the packing materials in the glass filter. When the discharge wall of the glass filter was filled with Hg(CN)2, the yield of acrylonitrile was at its maximum. When a mixture of propylene and hydrogen cyanide was discharged in an ozonizer in the absence of air, the main liquid products were crotononitrile, methacrylonitrile, and n-propyl cyanide. Besides these compounds, the reaction products were confirmed to consist of isopropyl cyanide, acetonitrile, acrylonitrile, 4-methyl-1-pentene, 2,3-dimethylbutane, 1,5-hexadiene, 2-methylpentane, 1-hexene, n-hexane, and gaseous products. Judging from the relative concentration of each compound in the reaction products, it may be said that 2-methylvinyl, isopropenyl, propyl, allyl, isopropyl, and cyano radicals are the main intermediates in this reaction system.