Cyclopropenylidene

Last updated
Cyclopropenylidene
Structural formula Cyclopropenylidene.png
Structural formula
Ball-and-stick model Cyclopropenylidene-3D-balls.png
Ball-and-stick model
Names
Preferred IUPAC name
Cycloprop-2-en-1-ylidene
Identifiers
3D model (JSmol)
ChemSpider
PubChem CID
  • InChI=1S/C3H2/c1-2-3-1/h1-2H
    Key: VVLPCWSYZYKZKR-UHFFFAOYSA-N
  • InChI=1/C3H2/c1-2-3-1/h1-2H
    Key: VVLPCWSYZYKZKR-UHFFFAOYAY
  • C1=C[C]1
Properties
C3H2
Molar mass 38.049 g·mol−1
Conjugate acid Cyclopropenium ion
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Cyclopropenylidene, or c-C3H2, is a partially aromatic molecule belonging to a highly reactive class of organic molecules known as carbenes. On Earth, cyclopropenylidene is only seen in the laboratory due to its reactivity. However, cyclopropenylidene is found in significant concentrations in the interstellar medium (ISM) and on Saturn's moon Titan. Its C2v symmetric isomer, propadienylidene (CCCH2) is also found in the ISM, but with abundances about an order of magnitude lower. [1] A third C2 symmetric isomer, propargylene (HCCCH), has not yet been detected in the ISM, most likely due to its low dipole moment.

Contents

History

The astronomical detection of c-C3H2 was first confirmed in 1985. [2] Four years earlier, several ambiguous lines had been observed in the radio region of spectra taken of the ISM, [3] but the observed lines were not identified at the time. These lines were later matched with a spectrum of c-C3H2 using an acetylene-helium discharge. Surprisingly, c-C3H2 has been found to be ubiquitous in the ISM. [4] Detections of c-C3H2 in the diffuse medium were particularly surprising because of the low densities. [5] [6] It had been believed that the chemistry of the diffuse medium did not allow for the formation of larger molecules, but this discovery, as well as the discovery of other large molecules, continue to illuminate the complexity of the diffuse medium. More recently, observations of c-C3H2 in dense clouds have also found concentrations that are significantly higher than expected. This has led to the hypothesis that the photodissociation of polycyclic aromatic hydrocarbons (PAHs) enhances the formation of c-C3H2. [7]

Titan (Moon of Saturn)

On 15 October 2020, it was announced that small amounts of cyclopropenylidene had been found in the atmosphere of Titan, the largest moon of Saturn. [8]

Formation

The formation reaction of c-C3H2 has been speculated to be the dissociative recombination of c-C
3H+
3. [9]

C
3H+
3 + e− → C3H2 + H

c-C
3H+
3 is a product of a long chain of carbon chemistry that occurs in the ISM. Carbon insertion reactions are crucial in this chain for forming C
3H+
3. However, as for most ion-molecule reactions speculated to be important in interstellar environments, this pathway has not been verified by laboratory studies. The protonation of ammonia by c-C
3H+
3 is another formation reaction. However, under typical dense cloud conditions, this reaction contributes less than 1% of the formation of C3H2.

Crossed molecular beam experiments indicate that the reaction of the methylidyne radical (CH) with acetylene (C2H2) forms cyclopropenylidene plus atomic hydrogen and also propadienylidene plus atomic hydrogen. [10] The neutral–neutral reaction between atomic carbon and the vinyl radical (C2H3) also forms cyclopropenylidene plus atomic hydrogen. [11] Both reactions are rapid at 10  K and have no entrance barrier and provide efficient formation pathways in cold interstellar environments and hydrocarbon-rich atmospheres of planets and their moons. [12]

Matrix isolated cyclopropenylidene has been prepared by flash vacuum thermolysis of a quadricyclane derivative in 1984. [13]

Destruction

Cyclopropenylidene is generally destroyed by reactions between ions and neutral molecules. Of these, protonation reactions are the most common. Any species of the type HX+ can react to convert the c-C3H2 back to c-C
3H+
3. [9] Due to rate constant and concentration considerations, the most important reactants for the destruction of c-C3H2 are HCO+, H+
3, and H3O+. [14]

C3H2 + HCO+ → C
3H+
3 + CO

Notice that c-C3H2 is mostly destroyed by converting it back to C
3H+
3. Since the major destruction pathways only regenerate the major parent molecule, C3H2 is essentially a dead end in terms of interstellar carbon chemistry. However, in diffuse clouds or in the photodissociation region (PDR) of dense clouds, the reaction with C+ becomes much more significant and C3H2 can begin to contribute to the formation of larger organic molecules.

Spectroscopy

Detections of c-C3H2 in the ISM rely on observations of molecular transitions using rotational spectroscopy. Since c-C3H2 is an asymmetric top, the rotational energy levels are split and the spectrum becomes complicated. Also, it should be noticed that C3H2 has spin isomers much like the spin isomers of hydrogen. These ortho and para forms exist in a 3:1 ratio and should be thought of as distinct molecules. Although the ortho and para forms look identical chemically, the energy levels are different, meaning that the molecules have different spectroscopic transitions.

When observing c-C3H2 in the interstellar medium, there are only certain transitions that can be seen. In general, only a few lines are available for use in astronomical detection. Many lines are unobservable because they are absorbed by the Earth's atmosphere. The only lines that can be observed are those that fall in the radio window. The more commonly observed lines are the 110 to 101 transition at 18343 MHz and the 212 to 101 transition at 85338 MHz of ortho-c-C3H2. [2] [4] [7]

See also

Related Research Articles

Aromatic compounds are those chemical compounds that contain one or more rings with pi electrons delocalized all the way around them. In contrast to compounds that exhibit aromaticity, aliphatic compounds lack this delocalization. The term "aromatic" was assigned before the physical mechanism determining aromaticity was discovered, and referred simply to the fact that many such compounds have a sweet or pleasant odour; however, not all aromatic compounds have a sweet odour, and not all compounds with a sweet odour are aromatic compounds. Aromatic hydrocarbons, or arenes, are aromatic organic compounds containing solely carbon and hydrogen atoms. The configuration of six carbon atoms in aromatic compounds is called a "benzene ring", after the simple aromatic compound benzene, or a phenyl group when part of a larger compound.

Interstellar cloud Accumulation of gas, plasma, and dust in space

An interstellar cloud is generally an accumulation of gas, plasma, and dust in our and other galaxies. Put differently, an interstellar cloud is a denser-than-average region of the interstellar medium (ISM), the matter and radiation that exists in the space between the star systems in a galaxy. Depending on the density, size, and temperature of a given cloud, its hydrogen can be neutral, making an H I region; ionized, or plasma making it an H II region; or molecular, which are referred to simply as molecular clouds, or sometime dense clouds. Neutral and ionized clouds are sometimes also called diffuse clouds. An interstellar cloud is formed by the gas and dust particles from a red giant in its later life.

In chemistry, hydronium is the common name for the aqueous cation H
3O+
, the type of oxonium ion produced by protonation of water. It is often viewed as the positive ion present when an Arrhenius acid is dissolved in water, as Arrhenius acid molecules in solution give up a proton to the surrounding water molecules. In actual fact, acids must be surrounded by more than a single water molecule in order to ionize, yielding aqueous H+ and conjugate base. Three main structures for the aqueous proton have garnered experimental support: The Eigen cation, which is a tetrahydrate, H3O+(H2O)3; the Zundel cation, which is a symmetric dihydrate, H+(H2O)2; and the Stoyanov cation, an expanded Zundel cation, which is a hexahydrate: H+(H2O)2(H2O)4. Spectroscopic evidence from well-defined IR spectra overwhelmingly supports the Stoyanov cation as the predominant form. For this reason, it has been suggested that wherever possible, the symbol H+(aq) should be used instead of the hydronium ion.

Buckminsterfullerene Carbon allotrope

Buckminsterfullerene is a type of fullerene with the formula C60. It has a cage-like fused-ring structure (truncated icosahedron) that resembles a soccer ball, made of twenty hexagons and twelve pentagons. Each carbon atom has three bonds. It is a black solid that dissolves in hydrocarbon solvents to produce a violet solution. The compound has received intense study, although few real world applications have been found.

Interstellar medium Matter and radiation in the space between the star systems in a galaxy

In astronomy, the interstellar medium (ISM) is the matter and radiation that exist in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as dust and cosmic rays. It fills interstellar space and blends smoothly into the surrounding intergalactic space. The energy that occupies the same volume, in the form of electromagnetic radiation, is the interstellar radiation field.

Astrochemistry is the study of the abundance and reactions of molecules in the Universe, and their interaction with radiation. The discipline is an overlap of astronomy and chemistry. The word "astrochemistry" may be applied to both the Solar System and the interstellar medium. The study of the abundance of elements and isotope ratios in Solar System objects, such as meteorites, is also called cosmochemistry, while the study of interstellar atoms and molecules and their interaction with radiation is sometimes called molecular astrophysics. The formation, atomic and chemical composition, evolution and fate of molecular gas clouds is of special interest, because it is from these clouds that solar systems form.

Hydroxyl radical Neutral form of the hydroxide ion (OH−)

The hydroxyl radical is the diatomic molecule •
OH. The hydroxyl radical is very stable as a dilute gas, but it decays very rapidly in the condensed phase. It is pervasive in some situations. Most notably the hydroxyl radicals is produced from the decomposition of hydroperoxides (ROOH) or, in atmospheric chemistry, by the reaction of excited atomic oxygen with water. It is also important radiation chemistry, since it leads to the formation of hydrogen peroxide and oxygen, which can enhance corrosion and SCC in coolant systems subjected to radioactive environments.

Diffuse interstellar bands

Diffuse interstellar bands (DIBs) are absorption features seen in the spectra of astronomical objects in the Milky Way and other galaxies. They are caused by the absorption of light by the interstellar medium. Circa 500 bands have now been seen, in ultraviolet, visible and infrared wavelengths.

Cosmic dust Dust floating in space

Cosmic dust, also called extraterrestrial dust or space dust, is dust which exists in outer space, or has fallen on Earth. Most cosmic dust particles measure between a few molecules and 0.1 mm. Larger particles are called meteoroids. Cosmic dust can be further distinguished by its astronomical location: intergalactic dust, interstellar dust, interplanetary dust and circumplanetary dust.

Trihydrogen cation Ion

The trihydrogen cation or protonated molecular hydrogen is a cation with formula H+
3, consisting of three hydrogen nuclei (protons) sharing two electrons.

Ethynyl radical Chemical compound

The ethynyl radical is an organic compound with the chemical formula C≡CH. It is a simple molecule that does not occur naturally on Earth but is abundant in the interstellar medium. It was first observed by electron spin resonance isolated in a solid argon matrix at liquid helium temperatures in 1963 by Cochran and coworkers at the Johns Hopkins Applied Physics Laboratory. It was first observed in the gas phase by Tucker and coworkers in November 1973 toward the Orion Nebula, using the NRAO 11-meter radio telescope. It has since been detected in a large variety of interstellar environments, including dense molecular clouds, bok globules, star forming regions, the shells around carbon-rich evolved stars, and even in other galaxies.

Hydrogen isocyanide is a chemical with the molecular formula HNC. It is a minor tautomer of hydrogen cyanide (HCN). Its importance in the field of astrochemistry is linked to its ubiquity in the interstellar medium.

Propynylidyne is a chemical compound that has been identified in interstellar space.

Interstellar formaldehyde (a topic relevant to astrochemistry) was first discovered in 1969 by L. Snyder et al. using the National Radio Astronomy Observatory. Formaldehyde (H2CO) was detected by means of the 111 - 110 ground state rotational transition at 4830 MHz. On 11 August 2014, astronomers released studies, using the Atacama Large Millimeter/Submillimeter Array (ALMA) for the first time, that detailed the distribution of HCN, HNC, H2CO, and dust inside the comae of comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON).

Cyano radical Chemical compound

The cyano radical (or cyanido radical) is a radical with molecular formula CN, sometimes written •CN. The cyano radical was one of the first detected molecules in the interstellar medium, in 1938. Its detection and analysis was influential in astrochemistry. The discovery was confirmed with a coudé spectrograph, which was made famous and credible due to this detection. ·CN has been observed in both diffuse clouds and dense clouds. Usually, CN is detected in regions with hydrogen cyanide, hydrogen isocyanide, and HCNH+, since it is involved in the creation and destruction of these species.

Cyanopolyynes are a group of chemicals with the chemical formula HC
nN (n = 3,5,7,...). Structurally, they are polyynes with a cyano group covalently bonded to one of the terminal acetylene units. A rarely seen group of molecules both due to the difficulty in production and the unstable nature of the paired groups, the cyanopolyynes have been observed as a major organic component in interstellar clouds. This is believed to be due to the hydrogen scarcity of some of these clouds. Interference with hydrogen is one of the reason for the molecule's instability due to the energetically favorable dissociation back into hydrogen cyanide and acetylene.

Imidogen Inorganic radical with the chemical formula NH

Imidogen is an inorganic compound with the chemical formula NH. Like other simple radicals, it is highly reactive and consequently short-lived except as a dilute gas. Its behavior depends on its spin multiplicity, i.e. the triplet versus singlet ground state.

Isobutyronitrile Chemical compound

Isobutyronitrile is a complex organic molecule that has been recently found in several meteorites arrived from space. The singularity of this chemical is due to the fact that it is the only one among the molecules arriving from the universe that has a branched, rather than straight, carbon backbone which is larger than usual, in comparison with others.

Formamide-based prebiotic chemistry refers to ongoing scientific efforts aimed at reconstructing the beginnings of life on our planet assuming that formamide could accumulate in sufficiently high amounts to serve as the building block and reaction medium for the synthesis of the first biogenic molecules.

References

  1. ↑ David Fossé; et al. (2001). "Molecular Carbon Chains and Rings in TMC-1". The Astrophysical Journal. doi: 10.1086/320471 .
  2. 1 2 P. Thaddeus, J. M. Vrtilek, and C. A. Gottlieb "Laboratory and Astronomical Identification of Cyclopropenylidene, C3H2." Astrophys. J.299 L63 (1985)
  3. ↑ P. Thaddeus, M. Guelin, R. A. Linke "Three New "Nonterrestrial" Molecules" Astrophys. J.246 L41 (1981)
  4. 1 2 Lucas, R. and Liszt, H. "Comparative chemistry of diffuse clouds I. C2H and C3H2" Astron. & Astrophys., 358, 1069 (2000)
  5. ↑ H. E. Matthews and W. M. Irvine "The Hydrocarbon Ring C3H2 is Ubiquitous in the Galaxy" Astrophys. J., 298, L61 (1985)
  6. ↑ P. Cox, R. Gusten, and C. Henkel "Observations of C3H2 in the Diffuse Interstellar Medium" Astron. & Astrophys., 206, 108 (1988)
  7. 1 2 J. Pety et al. "Are PAHs precursors of small hydrocarbons in photo-dissociation regions? The Horsehead case" Astron. & Astrophys., 435, 885 (2005)
  8. ↑ C.A. Nixon et al. "Detection of Cyclopropenylidene on Titan with ALMA" J. Astron., 160-5 (2020)
  9. 1 2 S. A. Maluendes, A. D. McLean, E. Herbst "Calculations Concerning Interstellar Isomeric Abundance Ratios for C3H and C3H2" Astrophys. J., 417 181 (1993)
  10. ↑ P. Maksyutenko, F. Zhang, X. Gu, R.I. Kaiser, "A Crossed Molecular Beam Study on the Reaction of Methylidyne Radicals [CH(X2Π)] with Acetylene [C2H2(X1Σ+
    g    )] – Competing C3H2 + H and C3H + H2 Channels", Chem. Phys Phys. Chem.13, 240-252 (2011).
  11. ↑ A.V. Wilson, D.S.N. Parker, F. Zhang, R.I. Kaiser, "Crossed Beam Study of the Atom-Radical Reaction of Ground State Carbon Atoms (C(3P)) with the Vinyl Radical (C2H3(X2A′))", Phys. Chem. Chem. Phys, 14, 477-481 (2012).
  12. ↑ R.I. Kaiser, "Experimental Investigation on the Formation of Carbon-Bearing Molecules in the Interstellar Medium via Neutral–Neutral Reactions", Chem. Rev., 102, 1309-1358 (2002).
  13. ↑ Hans P. Reisenauer, Günther Maier, Achim Riemann and Reinhard W. Hoffmann "Cyclopropenylidene" Angew. Chem. Int. Ed. Engl., 23 641 (1984)
  14. ↑ T. J. Millar, P. R. A. Farquhar, K. Willacy "The UMIST Database for Astrochemistry 1995" Astron. and Astrophys. Sup., 121 139 (1997)
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