Propyne Molecules Research Articles

Infrared spectroscopy of isomers of C3H4+ in superfluid helium droplets.

Superfluid helium nanodroplets are unique nanomatrices for the isolation and study of transient molecular species, such as radicals, carbenes, and ions. In this work, isomers of C3H4+ were produced upon electron ionization of propyne and allene molecules and interrogated via infrared spectroscopy inside He nanodroplet matrices. It was found that the spectrum of C3H4+ has at least three distinct groups of bands. The relative intensities of the bands depend on the precursor employed and its pickup pressure, which indicates the presence of at least three different isomers. Two isomers were identified as allene and propyne radical cations. The third isomer, which has several new bands in the range of 3100-3200cm-1, may be the elusive vinylmethylene H2C=CH-CH+ radical cation. The observed bands for the allene and propyne cations are in good agreement with the results of density functional theory calculations. However, there is only moderate agreement between the new bands and the theoretically calculated vinylmethylene spectrum, which indicates more work is necessary to unambiguously assign it.

Collisional excitation of propyne (CH3CCH) by He atoms

Context. A detailed interpretation of the detected emission lines of environments where propyne (or methyl acetylene, CH3CCH) is observed requires access to its collisional rate coefficients with the most abundant species in the interstellar medium, namely, helium (He) or molecular hydrogen (H2). Aims. We present the first three-dimensional potential energy surface (3D PES) for the CH3CCH-He molecular complex. We study the dynamics of the collision and report the first set of rate coefficients for temperatures up to 100 K for the collisional excitation of the lowest 60 ortho rotational levels and 60 para rotational levels of CH3CCH by He atoms. Methods. We computed the 3D PES with the explicitly correlated coupled-cluster with a single-, double-, and perturbative triple-excitation method in conjunction with the augmented correlation-consistent triple zeta basis set (CCSD(T)-F12a/aug-cc-pVTZ). The 3D PES was then fitted to an analytical function and scattering computations of pure rotational (de-)excitation of CH3CCH by collision with He atoms were performed. State-to-state cross-sections were computed using the close coupling method for total energies up to 100 cm−1 and with the coupled states approximation at higher energies for both the ortho- and para- symmetries of CH3CCH. Results. The PES we obtained is characterised by a large anisotropy and a potential well depth of 51.04 cm−1. By thermally averaging the collisional cross-sections, we determined the quenching rate coefficients for kinetic temperatures up to 100 K. A strong and even Δj propensity rule at almost all collision energies is present for CH3CCH-He complex. To evaluate the impact of rate coefficients on the analysis of observations, we carried out non-local thermodynamic equilibrium radiative transfer computations of the excitation temperatures and we demonstrate that local thermodynamic equilibrium conditions are not typically fulfilled for the propyne molecule.

Exploring human-guided strategies for reaction network exploration: Interactive molecular dynamics in virtual reality as a tool for citizen scientists.

The emerging fields of citizen science and gamification reformulate scientific problems as games or puzzles to be solved. Through engaging the wider non-scientific community, significant breakthroughs may be made by analyzing citizen-gathered data. In parallel, recent advances in virtual reality (VR) technology are increasingly being used within a scientific context and the burgeoning field of interactive molecular dynamics in VR (iMD-VR) allows users to interact with dynamical chemistry simulations in real time. Here, we demonstrate the utility of iMD-VR as a medium for gamification of chemistry research tasks. An iMD-VR "game" was designed to encourage users to explore the reactivity of a particular chemical system, and a cohort of 18 participants was recruited to playtest this game as part of a user study. The reaction game encouraged users to experiment with making chemical reactions between a propyne molecule and an OH radical, and "molecular snapshots" from each game session were then compiled and used to map out reaction pathways. The reaction network generated by users was compared to existing literature networks demonstrating that users in VR capture almost all the important reaction pathways. Further comparisons between humans and an algorithmic method for guiding molecular dynamics show that through using citizen science to explore these kinds of chemical problems, new approaches and strategies start to emerge.

Structural Evolution from Noninterpenetrated to Interpenetrated Thorium-Organic Frameworks Exhibiting High Propyne Storage.

Two thorium-organic frameworks of [Th6O4(OH)4(TFBPDC)6(H2O)6]n (Th-TFBPDC) and [Th6O4(OH)4(TFBPDC)4(HCOO)4(H2O)6]n (Th-TFBPDC-i) constructed from the 3,3',5,5'-tetrakis(fluoro)biphenyl-4,4'-dicarboxylate (TFBPDC2-) ligand were obtained in a reaction. At an early stage of the reaction, the formation of the three-dimensional (3D) framework of Th-TFBPDC was discovered. At a later stage of the reaction, the complete product of Th-TFBPDC-i was obtained. The structural evolution from a noninterpenetrated network of Th-TFBPDC to a 2-fold interpenetrated network of Th-TFBPDC-i is a dissolution-recrystallization process and rationalized as the four equatorial TFBPDC2- ligands in an octahedral [Th6O4(OH)4(TFBPDC)12] unit were displaced by four formate ligands to form a [Th6O4(OH)4(TFBPDC)8(HCOO)4] unit via a ligand substitution reaction. The large pore volume as well as the strong interactions between the host framework and guest propyne (C3H4) molecules demonstrated by computational results endow the highly water-stable Th-TFBPDC with the best-performing C3H4 storage under ambient conditions. This work presents a rare example of structural evolution from a 3D noninterpenetrated network to a 2-fold 3D interpenetrated network and a highly promising metal-organic framework (MOF) for C3H4 storage with a C3H4 uptake of 8.16 mmol g-1 at 298 K.

Cd-MOF: specific adsorption selectivity for linear alkyne (propyne, 2-butyne and phenylacetylene) molecules.

The selective adsorption of APPT-Cd-MOF 1 for propyne, 2-butyne and phenylacetylene was confirmed by single-crystal analysis. In addition, the selective adsorption performance of Cd-MOF for C3H4/C3H6/C3H8 was investigated. The matching of the functionality and size/shape between porous materials and guest molecules clarified the specific recognition of 1 for linear alkyne molecules.

Robust Microporous Metal-Organic Frameworks for Highly Efficient and Simultaneous Removal of Propyne and Propadiene from Propylene.

Simultaneous removal of trace amounts of propyne and propadiene from propylene is an important but challenging industrial process. We report herein a class of microporous metal-organic frameworks (NKMOF-1-M) with exceptional water stability and remarkably high uptakes for both propyne and propadiene at low pressures. NKMOF-1-M separated a ternary propyne/propadiene/propylene (0.5 : 0.5 : 99.0) mixture with the highest reported selectivity for the production of polymer-grade propylene (99.996 %) at ambient temperature, as attributed to its strong binding affinity for propyne and propadiene over propylene. Moreover, we were able to visualize propyne and propadiene molecules in the single-crystal structure of NKMOF-1-M through a convenient approach under ambient conditions, which helped to precisely understand the binding sites and affinity for propyne and propadiene. These results provide important guidance on using ultramicroporous MOFs as physisorbent materials.

Robust Microporous Metal–Organic Frameworks for Highly Efficient and Simultaneous Removal of Propyne and Propadiene from Propylene

AbstractSimultaneous removal of trace amounts of propyne and propadiene from propylene is an important but challenging industrial process. We report herein a class of microporous metal–organic frameworks (NKMOF‐1‐M) with exceptional water stability and remarkably high uptakes for both propyne and propadiene at low pressures. NKMOF‐1‐M separated a ternary propyne/propadiene/propylene (0.5 : 0.5 : 99.0) mixture with the highest reported selectivity for the production of polymer‐grade propylene (99.996 %) at ambient temperature, as attributed to its strong binding affinity for propyne and propadiene over propylene. Moreover, we were able to visualize propyne and propadiene molecules in the single‐crystal structure of NKMOF‐1‐M through a convenient approach under ambient conditions, which helped to precisely understand the binding sites and affinity for propyne and propadiene. These results provide important guidance on using ultramicroporous MOFs as physisorbent materials.

Mechanism study on the effect of alkali metal ions on the formation of HCN as NOx precursor during coal pyrolysis

Coal, as a typical fossil fuel, is a current major contributor to the global emission of nitrogen oxides (NOx). The NOx formation process during coal utilisation can be described as the thermal decomposition of N-containing model compounds into NOx precursors followed by NOx formation. The existence of alkali metal ions, Na+ and K+, during the coal utilisation process has a significant influence on the formation of NOx species. However, the information about this influence is currently lacking within the available literature. Within this research, the effect of Na+ and K+ on the formation mechanism of NOx during pyrrole pyrolysis were investigated using density functional theory (DFT). A hydrogen migration occurs from the meta-position of pyrrole-N is transferred to the ortho-position, and then pyrrole-N disconnected from the ortho-position C, which makes the ring opened. Lastly, in a concerted mechanism, a long carbon bond breaking between the migrating hydrogen and the carbon, nitrogen atoms. It was found that Na+ and K+ have a catalytic effect on the internal hydrogen transfer and ring-opening of pyrrole but have an inhibitory effect on internal hydrogen isomerization and concerted decomposition reaction. It was also found that those alkali metal ions (Na+ and K+) have strong interactions with pyrrole and its derived compounds (HCN and propyne molecules), those interactions are much larger than the existing attractive interactions among HCN, propyne molecules and their complexes. Additionally, it was found that both Na+ and K+ inhibit the HCN formation step from pyrrole pyrolysis, with Na+, has a higher inhibition effect than that of K+. Furthermore, the mechanisms discussed in this research may well play a role in the thermal decomposition of other coal compounds such as indole and carbazole.

Electron-scattering cross sections for selected alkyne molecules: Measurements and calculations

We report cross-section results from experimental and theoretical studies on electron collisions with 1-butyne ($\text{HC}\ensuremath{\equiv}\text{C}--{\text{CH}}_{2}{\text{CH}}_{3}$) and acetylene ($\text{HC}\ensuremath{\equiv}\text{CH}$) molecules and from computations for a propyne ($\text{HC}\ensuremath{\equiv}\text{C}--{\text{CH}}_{3}$) molecule. Absolute $grand\phantom{\rule{0.16em}{0ex}}$-total electron-scattering cross sections (TCSs) were measured at impact energies ranging from about 0.5 to 300 eV using the linear electron-transmission method. The TCS energy curve for 1-butyne has a very broad enhancement on which some distinct features are superimposed, namely a resonant-like maximum (located near 3.2 eV), a broad hump (centered around 7.5 eV), and a shoulder (spanned between 12 and 26 eV). The shape of our experimental TCS curve for acetylene closely resembles that reported earlier, while its magnitude is usually larger. As no previous calculations for electron collisions with 1-butyne and propyne are disclosed in the literature, we computed the elastic (ECS) and ionization (ICS) cross sections for these molecules. Similar calculations were also performed for acetylene molecules. The additivity rule was employed to calculate the ECSs from 50 to 3000 eV, while the binary-encounter-Bethe approach was used for computation of the ICSs, from the threshold up to 3000 eV. The sum (ECS + ICS) of these two computed cross sections reasonably reproduces the TCS measurements above 50 eV. Furthermore, the experimental TCS curves, obtained in our laboratory, for a series of acetylenic compounds---acetylene ($\text{HC}\ensuremath{\equiv}\text{CH}$), propyne ($\text{HC}\ensuremath{\equiv}\text{C}--{CH}_{3}$), and 1-butyne ($\text{HC}\ensuremath{\equiv}\text{C}--{\text{CH}}_{2}{\text{CH}}_{3}$)---are compared to study the substitutional effect. Finally, the influence of the structural differences on the electron-scattering TCS for isomers of the ${\text{C}}_{4}{\text{H}}_{6}$ molecule (1-butyne, 2-butyne, and 1,3--butadiene) is indicated and discussed.

Infrared and Raman Spectroscopy: A Discovery-Based Activity for the General Chemistry Curriculum

A discovery-based method is described for incorporating the concepts of IR and Raman spectroscopy into the general chemistry curriculum. Students use three sets of springs to model the properties of single, double, and triple covalent bonds. Then, Gaussian 03W molecular modeling software is used to illustrate the relationship between bond vibrations and both IR and Raman spectroscopy. Students view the characteristic vibrations of C–C, C═C, and C≡C bonds in propane, propene, and propyne molecules. Finally, students collect IR and Raman spectra of hexane, 1-hexene, and 1-heptyne. This series of activities is completed in the first semester of the general chemistry sequence following the development of Lewis structures and before the discussion of electronegativity and bond polarity.

10.1007/s11447-008-1003-6

The dynamics of intramolecular vibrational energy redistribution from the initially excited νHC mode in the propyne molecule (H-C≡C-CH3), as well as in three its derivatives that are obtained by replacing one of the hydrogen atoms of the methyl group with the chlorine atom (propargylchloride), the OH radical (propargyl alcohol), or with the NH2 radical (propargylamine), has been studied. Probing was performed by anti-Stokes spontaneous Raman scattering. The measured values of the deexcitation rate W of the νHC mode lie in the range 109−1010 s−1. A significant feature of the dynamics—an incomplete energy redistribution from the νHC mode—is especially clearly pronounced for the H-C≡C-CH3 and H-C≡C-CH2Cl molecules, for which the values of the relative level σ of the residual energy in the νHC mode are approximately equal to 0.54 and 0.25, respectively. A theoretical analysis performed made it possible to relate the parameters W and σ, on the one hand, and the density ρ of the so-called bath states, which are responsible for the vibrational energy redistribution, on the other hand. It is shown that, for all the four molecules considered, the required values of ρ can be accounted for solely by a strong vibrational-rotational mixing in the bath, as a result of which the projection of the total angular momentum onto the axis of the molecule ceases to be “good” quantum number.

ChemInform Abstract: Key Influence of the Nature of the Substituent in the Propynal Molecule on the Outcome of Its Reaction with Vicinal Di(N‐hydroxyamine).

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Key influence of the nature of the substituent in the propynal molecule on the outcome of its reaction with vicinal di(N-hydroxyamine)

The reaction of propynals X-C≡C-CHO, where X = Alk or Ar, with 2,3-di(N-hydroxyamino)-2,3-dimethylbutane gives exclusively 1-X-2-(1-hydroxy-4,4,5,5-tetramethylimidazolidin-2-ylidene)ethanones. In the case of X = Me3Si, the reaction affords 2-(2-trimethylsilylethynyl)-4,4,5,5-tetramethylimidazolidine-1,3-diol. The reaction of propynal containing X = Et3Ge yields both types of the products. The resulting imidazolidine-1,3-diol can be quantitatively isomerized to imidazolidin-2-ylideneethanone, oxidized to 2-[2-(triethylgermyl)ethynyl]-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl, or transformed into ethynyl-substituted nitronyl nitroxide.

Theoretical Study on the Reaction Mechanism of VO2+ with Propyne in Gas Phase

Possible molecular mechanisms of the gas-phase ion/molecule reaction of VO2+ in its lowest singlet and triplet states (1A1/3A' ') with propyne have been investigated theoretically by density functional theory (DFT) methods. The geometries, energetic values, and bonding features of all stationary and intersystem crossing points involved in the five different reaction pathways (paths 1-5), in both high-spin (triplet) and low-spin (singlet) surfaces, are reported and analyzed. The oxidation reaction starts by a hydrogen transfer from propyne molecule to the vanadyl complex, followed by oxygen migration to the hydrocarbon moiety. A hydride transfer process to the vanadium atom opens four different reaction courses, paths 1-4, while path 5 arises from a hydrogen transfer process to the hydroxyl group. Five crossing points between high- and low-spin states are found: one of them takes place before the first branching point, while the others occur along path 1. Four different exit channels are found: elimination of hydrogen molecule to yield propynaldehyde and VO+ (1Sigma/3Sigma); formation of propynaldehyde and the moiety V-(OH2)+; and two elimination processes of water molecule to yield cationic products, Prod-fc+ and Prod-dc+ where the vanadium atom adopts a four- and di-coordinate structure, respectively.

Intramolecular vibrational dynamics of propyne and its derivatives: The role of vibrational-rotational mixing

The dynamics of intramolecular vibrational energy redistribution from the initially excited νHC mode in the propyne molecule (H-C≡C-CH3), as well as in three its derivatives that are obtained by replacing one of the hydrogen atoms of the methyl group with the chlorine atom (propargylchloride), the OH radical (propargyl alcohol), or with the NH2 radical (propargylamine), has been studied. Probing was performed by anti-Stokes spontaneous Raman scattering. The measured values of the deexcitation rate W of the νHC mode lie in the range 109−1010 s−1. A significant feature of the dynamics—an incomplete energy redistribution from the νHC mode—is especially clearly pronounced for the H-C≡C-CH3 and H-C≡C-CH2Cl molecules, for which the values of the relative level σ of the residual energy in the νHC mode are approximately equal to 0.54 and 0.25, respectively. A theoretical analysis performed made it possible to relate the parameters W and σ, on the one hand, and the density ρ of the so-called bath states, which are responsible for the vibrational energy redistribution, on the other hand. It is shown that, for all the four molecules considered, the required values of ρ can be accounted for solely by a strong vibrational-rotational mixing in the bath, as a result of which the projection of the total angular momentum onto the axis of the molecule ceases to be “good” quantum number.

Use of helium nanodroplets for assembly, transport, and surface deposition of large molecular and atomic clusters

The utility of continuous beam of helium droplets for assembly, transport, and surface deposition of metal and molecular clusters is studied. Clusters of propyne having from about 10 to 10(4) molecules were obtained via sequential pickup of molecules by He droplets with average sizes in the range of 10(4)-10(7) atoms. The maximum attainable flux of the propyne molecules carried by He droplets was found to be in the range of (5-15)x10(15) molecules sr(-1) s(-1), being larger in larger droplets. The size of the clusters and the flux of the transported species are ultimately limited by the evaporative extinction of the entire helium droplet upon capture of particles. It is shown that the attenuation of the He droplet beam in the process of the cluster growth can be used in order to obtain the average size and the binding energy of the clusters. Furthermore, we used He droplets for assembling and surface deposition of gold and silver clusters having about 500 atoms. Typical deposition rate of metal atoms of about 3 x 10(15) atoms sr(-1) s(-1) is comparable to or larger than obtained with other beam deposition techniques. We propose that doping of He droplets by Au and Ag atoms in two separate pickup chambers leads to formation of the bimetal clusters having core-shell structure.

Global Mapping of Equilibrium and Transition Structures on Potential Energy Surfaces by the Scaled Hypersphere Search Method: Applications to ab Initio Surfaces of Formaldehyde and Propyne Molecules

Technical details of a new global mapping technique for finding equilibrium (EQ) and transition structures (TS) on potential energy surfaces (PES), the scaled hypersphere search (SHS) method (Ohno, K.; Maeda, S. Chem. Phys. Lett. 2004, 384, 277), are presented. On the basis of a simple principle that reaction pathways are found as anharmonic downward distortions of PES around an EQ point, the reaction pathways can be obtained as energy minima on the scaled hypersphere surface, which would have a constant energy when the potentials are harmonic. Connections of SHS paths between each EQ are very similar to corresponding intrinsic reaction coordinate (IRC) connections. The energy maximum along the SHS path reaches a region in close proximity to the TS of the reaction pathway, and the subsequent geometry optimization from the SHS maximum structure easily converges to the TS. The SHS method, using the one-after-another algorithm connecting EQ and TS, considerably reduces the multidimensional space to be searched to certain limited regions around the pathways connecting each EQ with the neighboring TS. Applications of the SHS method have been made to ab initio surfaces of formaldehyde and propyne molecules to obtain systematically five EQ and nine TS for formaldehyde and seven EQ and 32 TS for propyne.

Propyne and allene photolysis at 193.3 nm and at 121.6 nm

The fragmentation dynamics of allene and propyne molecules following photoexcitation at 193.3 nm and at 121.6 nm have been investigated by H(D) Rydberg atom photofragment translational spectroscopy. The total kinetic energy release (TKER) spectra of the H (and D) atoms resulting from H2CCCH2, H3CCCH, and D3CCCH photolysis at 193.3 nm are found to be essentially identical. The results contradict conclusions reached in several previous studies of propyne photochemistry at this wavelength. The observed energy disposal, and the isomer independence, are most readily rationalized by assuming that the fragmentation of both molecules following excitation at 193.3 nm is preceded by internal conversion to the ground (S0) state potential energy surface, and that the isomerization rate of the resulting highly vibrationally excited S0 molecules is faster than their unimolecular decay rate. The time-of-flight (TOF) and TKER spectra of the H and D atoms resulting from 121.6 nm photolysis of allene, propyne and propyne-d3 show significant differences, however. The differences can be reconciled by assuming two competing pathways for forming H(D) atoms following photoexcitation of propyne. One, involving selective cleavage of the acetylenic H3CCC–H bond, is assumed to occur from the excited electronic state prepared by photon absorption or from a recognizably “propynelike” state to which it couples efficiently. The other, which yields a slower distribution of H(D) atoms, is considered to arise via radiationless transfer to a lower electronic state, isomerization, and subsequent unimolecular decay. The TOF and TKER spectra of the H atoms resulting from 121.6 nm photolysis of allene are indistinguishable from those associated with this second, “statistical” fragmentation channel in propyne.

Near ultraviolet photodissociation of allene and propyne

The fragmentation dynamics of allene and propyne molecules following photoexcitation at 203.3, 209.0 and 213.3 nm have been investigated by H (Rydberg) atom photofragment translational spectroscopy methods. Contrary to conclusions reached in previous photochemical studies of these molecules, at a photolysis wavelength of 193 nm, we find the translational energy spectra associated with the H atom product forming channel in both molecules to be essentially identical, and to have a form that is reproduced well by an approximate statistical model that assumes population of all possible vibrational states of the H2CCCH partner. Such behavior can be most readily accommodated by assuming that, for both molecules, at the excitation energies used in the present work, internal conversion to, and isomerization on, the ground state potential energy surface precedes fragmentation.

Reaction between the thiocarbonyl complex, Os(CS)(CO)(PPh 3) 3, and propyne: crystal structure of a new sulfur-substituted osmabenzene

Reaction between Os(CS)(CO)(PPh 3) 3 and propyne gives a complex mixture of products from which can be isolated the simple oxidative addition product Os(CCMe)H(CS)(CO)(PPh 3) 2 ( 1) and the osmabenzene Os(η 2-C[S]CMeCHCHC Me)(CO)(PPh 3) 2 ( 2), where the two propyne molecules in the osmabenzene ring have linked tail-to-tail. Treatment of 1 with HCl gives, as the ultimate product, the propenylthioacyl complex, Os(η 2-C[S]CHCHMe)Cl(CO)(PPh 3) 2 ( 3). The crystal structures of compounds 1– 3 have been determined.