Propargyl Research Articles

Divergent Synthesis of CF3 -Substituted Allenyl Nitriles by Ligand-Controlled Radical 1,2- and 1,4-Addition to 1,3-Enynes.

A ligand-controlled system that enables regioselective trifluoromethylcyanation of 1,3-enynes has been identified, which provides access to a variety of CF3 -containing tri- and tetrasubstituted allenyl nitriles. We disclose that the involved propargylic radicals can be selectively trapped by (Box)CuII cyanide, while the tautomerized allenyl radicals are trapped by (phen)CuII cyanide (Box= bisoxazoline, phen=phenanthroline). In addition, the reaction features broad substrate scope and excellent functional group compatibility. Moreover, this protocol represents a novel regioselectivity-tunable functionalization of 1,3-enynes via radicals, which we believe will have great implications for the development of catalytic systems for selectivity control in radical and organometallic chemistry.

Divergent Synthesis of CF3‐Substituted Allenyl Nitriles by Ligand‐Controlled Radical 1,2‐ and 1,4‐Addition to 1,3‐Enynes

AbstractA ligand‐controlled system that enables regioselective trifluoromethylcyanation of 1,3‐enynes has been identified, which provides access to a variety of CF3‐containing tri‐ and tetrasubstituted allenyl nitriles. We disclose that the involved propargylic radicals can be selectively trapped by (Box)CuII cyanide, while the tautomerized allenyl radicals are trapped by (phen)CuII cyanide (Box= bisoxazoline, phen=phenanthroline). In addition, the reaction features broad substrate scope and excellent functional group compatibility. Moreover, this protocol represents a novel regioselectivity‐tunable functionalization of 1,3‐enynes via radicals, which we believe will have great implications for the development of catalytic systems for selectivity control in radical and organometallic chemistry.

Dynamics of the C(3P) + Ethylene Reaction: A Trajectory Surface Hopping Study.

The direct dynamics trajectory surface hopping (DDTSH) method has been employed to study the reaction of C(3P) with ethylene (C2H4). Our trajectory simulations show that at a reagent collision energy of 7.36 kcal/mol, there are two possible product channels: propargyl (H2CCCH) + H and carbene (CH2) + acetylene (HCCH). Estimated branching ratios based on trajectory propagations indicate that propargyl radical formation is the dominant channel contributing (94.1 ± 5.2) % of the overall products formation with (5.9 ± 1.7)% contribution from the minor CH2 + HCCH channel. These findings are consistent with earlier experimental observations and theoretical predictions that propargyl (H2CCCH) formation is the dominant channel for the C(3P) + C2H4 collision reaction. Our trajectory simulations, however, unravel five distinctly different dynamical pathways, unlike earlier experimental and theoretical predictions of only two pathways proposed for the formation of propargyl radical, and three different dynamics are followed for the CH2 + HCCH channel (this channel was not detected experimentally). The computed translational energy distribution for the propargyl + H channel is narrower and showed peak maximum at a lower energy compared to the experimental one. While the center of mass product angular distribution based on our trajectory propagation is nearly isotropic in nature indicating formation of long-lived intermediate complexes, the experimental one was reported to be backward-forward distributed with more intensity in the forward direction indicating the formation of an osculating complex. Our trajectory surface hopping calculations confirm that the effect of intersystem crossing (ISC) is not important for the title reaction presumably because of weak spin-orbit coupling values (<10 cm-1) for the (C + C2H4) system. No trace of cyclic products formation was obtained from our trajectory simulations, which however was predicted to be a minor (2%) product channel, experimentally.

A comparative study on the sooting tendencies of various 1-alkene fuels in counterflow diffusion flames

Alkenes are important components in transportation fuels, and are known to have increased sooting tendencies compared to analogous saturated hydrocarbons with the same carbon number. This work aims to understand the sooting tendencies of various 1-alkenes through experiments and numerical simulations for counterflow diffusion flames. Soot and PAH formation tendencies of 1-alkene fuels, including ethylene (C2H4), propene (C3H6), 1-butene (1-C4H8), 1-pentene (1-C5H10), 1-hexene (1-C6H12) and 1-octene (1-C8H16), were experimentally studied using laser induced-incandescence (LII) and laser-induced fluorescence (LIF) techniques, respectively. From the LII results, 1-C4H8 was found to be the most sooting fuel, followed by C3H6 > 1-C5H10 > 1-C6H12 > 1-C8H16 > C2H4. The LIF data with a detection wavelength of 500 nm indicated the PAH formation tendencies followed the order of 1-C4H8 > 1-C5H10 ∼1-C6H12 > C3H6 > 1-C8H16 > C2H4, which were different from the order of sooting tendencies. Numerical simulations with a comprehensive chemical kinetic model including PAH growth chemistry for the tested 1-alkene fuels were conducted to elucidate the aromatic formation pathways and rationalize the experimentally observed trends. The numerical results highlighted the importance of intermediate species with odd carbon numbers in aromatic species formation, such as propargyl, allyl, cyclopentadienyl and indenyl radicals. Their concentration differences, which could be traced back to the parent fuel molecules through rate of production analysis, rationalize the experimentally observed differences in soot and PAH formation tendencies.

Modular Approach to Kekulé Diradicaloids Derived from Cyclic (Alkyl)(amino)carbenes.

A modular approach for the synthesis of Kekulé diradicaloids is reported. The key step is the insertion of a carbene, namely, a cyclic (alkyl)(amino)carbene (CAAC), into the C-H bonds of two terminal alkynes linked by a spacer. Subsequent hydride abstraction, followed by two-electron reduction of the corresponding bis(iminium) salts, affords the desired diradicaloids. This synthetic route readily allows for the installation of communicating spacers, featuring different degrees of aromaticity and lengths, and gives the possibility of generating unsymmetrical compounds with two different CAACs. Electron paramagnetic resonance (EPR), NMR, UV-vis, and X-ray studies in combination with quantum-chemical calculations give insight into the electronic nature of the deeply colored Kekulé diradicaloids. They feature a singlet ground state with varying degrees of diradical character in combination with small singlet/triplet gaps. Upon lengthening of the spacer, the properties of the compounds approach those of monoradicals in which steric protection of the propargyl radical moiety is necessary to inhibit decomposition pathways. Most of these diradicaloids are stable at room temperature, both in solution and in the solid state, but are highly oxygen-sensitive. They represent the first diradicaloids derived from iminium salts.

Experimental and modeling studies of small typical methyl esters pyrolysis: Methyl butanoate and methyl crotonate

In order to examine in detail the effect of C C bond on the combustion chemistry of biodiesel fuels, two C4 fatty acid methyl esters (FAMEs) were investigated, namely methyl butanoate (MB) and methyl crotonate (MC). Pyrolysis experiments of these two FAMEs at 30, 150 and 780 Torr were conducted in a flow reactor over the temperature range of 773–1323 K, using gas chromatography-mass spectrometry. A number of pyrolysis species including C1 to C4 hydrocarbons, oxygenated products, esters and aromatics were observed and identified. A comprehensive kinetic model for MB and MC combustion was developed, and applied to validate against the new experimental data. In this work, peak mole fraction of benzene, as well as other unsaturated hydrocarbons in MC pyrolysis, was found to be in slightly higher amounts in comparison with that of MB. Kinetic modeling analysis revealed that the dominant formation pathway of benzene was the self-combination reaction of propargyl radical. Furthermore, the model was also validated against the previous experimental data on MB and MC combustion, including oxidation in jet stirred reactor, pyrolysis in shock tube and laminar premixed flame. This study suggests that the effect of C C double bond in FAMEs might give rise to a growing tendency of initial PAH and soot precursors in the whole thermal decomposition process.

Isomer-specific detection in the UV photodissociation of the propargyl radical by chirped-pulse mm-wave spectroscopy in a pulsed quasi-uniform flow.

Isomer-specific detection and product branching fractions in the UV photodissociation of the propargyl radical is achieved through the use of chirped-pulse Fourier-transform mm-wave spectroscopy in a pulsed quasi-uniform flow (CPUF). Propargyl radicals are produced in the 193 nm photodissociation of 1,2-butadiene. Absorption of a second photon leads to H atom elimination giving three possible C3H2 isomers: singlets cyclopropenylidene (c-C3H2) and propadienylidene (l-C3H2), and triplet propargylene (3HCCCH). The singlet products and their appearance kinetics in the flow are directly determined by rotational spectroscopy, but due to the negligible dipole moment of propargylene, it is not directly monitored. However, we exploit the time-dependent kinetics of H-atom catalyzed isomerization to infer the branching to propargylene as well. We obtain the overall branching among H loss channels to be 2.9% (+1.1/-0.5) l-C3H2 + H, 16.8% (+3.2/-1.3) c-C3H2 + H, and 80.2 (+1.8/-4.2) 3HCCCH + H. Our findings are qualitatively consistent with earlier RRKM calculations in that the major channel in the photodissociation of the propargyl radical at 193 nm is to 3HCCCH + H; however, a greater contribution to the energetically most favorable isomer, c-C3H2 + H is observed in this work. We do not detect the predicted HCCC + H2 channel, but place an upper bound on its yield of 1%.

Numerical Investigation on 1,3-Butadiene/Propyne Co-pyrolysis and Insight into Synergistic Effect on Aromatic Hydrocarbon Formation

A numerical investigation on the co-pyrolysis of 1,3-butadiene and propyne is performed to explore the synergistic effect between fuel components on aromatic hydrocarbon formation. A detailed kinetic model of 1,3-butadiene/propyne co-pyrolysis with the sub-mechanism of aromatic hydrocarbon formation is developed and validated on previous 1,3-butadiene and propyne pyrolysis experiments. The model is able to reproduce both the single component pyrolysis and the co-pyrolysis experiments, as well as the synergistic effect between 1,3-butadiene and propyne on the formation of a series of aromatic hydrocarbons. Based on the rate of production and sensitivity analyses, key reaction pathways in the fuel decomposition and aromatic hydrocarbon formation processes are revealed and insight into the synergistic effect on aromatic hydrocarbon formation is also achieved. The synergistic effect results from the interaction between 1,3-butadiene and propyne. The easily happened chain initiation in the 1,3-butadiene decomposition provides an abundant radical pool for propyne to undergo the H-atom abstraction and produce propargyl radical which plays key roles in the formation of aromatic hydrocarbons. Besides, the 1,3-butadiene/propyne co-pyrolysis includes high concentration levels of C3 and C4 precursors simultaneously, which stimulates the formation of key aromatic hydrocarbons such as toluene and naphthalene.

Experimental and kinetic modeling studies of furan pyrolysis: Fuel decomposition and aromatic ring formation

The pyrolysis of furan was studied from 1100 to 1600K in a flow reactor at low pressure (30Torr). Synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) was used for isomeric identification and mole fraction measurements of the pyrolysis products, especially the free radicals. Specific products were observed and measured for the unimolecular decomposition reactions of furan, such as propyne+CO, acetylene+ketene and propargyl radical, etc. An updated combustion model of furan from Somers model was adopted to simulate the mole fraction profiles of the pyrolysis species measured in this work. Kinetic modeling analysis indicated that the decomposition of furan is mainly controlled by the unimolecular decomposition reactions under the investigated conditions. Based on the experimental results and theoretical simulations, propargyl radical is suggested to be mainly formed from the direct unimolecular decomposition of propyne instead of that of furan. In furan pyrolysis, propargyl and phenyl radicals are the most important precursors of large aromatic species.

Mystery of 1-Vinylpropargyl Formation from Acetylene Addition to the Propargyl Radical: An Open-and-Shut Case.

The addition of acetylene (C2H2) to the propargyl radical (C3H3) initiates a cascade of molecular weight growth reactions that result in the production of polycyclic aromatic hydrocarbons (PAHs) in flames. Although it is well-established that the first reaction step produces the cyclic C5H5 radical cyclopentadienyl (c-C5H5), recent studies have also detected significant quantities of the open-chain form, 1-vinylpropargyl (l-C5H5). This work presents a mechanism for the C3H3 + C2H2 reaction from ab initio calculations, which includes pathways for the formation of both the open and shut isomers as well as for their interconversion. Formation of both isomers proceeds from the initial HCCCH2CHCH• reaction adduct with similar barriers, both well below the entrance channel energy. Subsequent isomerization of l-C5H5 with c-C5H5 also transpires at below the energy of the reactants, although this process connects two deep wells (being resonance stabilized radicals), and must compete with collisional energy transfer. An RRKM theory/master equation model is developed for the reported C5H5 reaction mechanism. Master equation simulations suggest that both cyclic and open-chain isomers are expected to form from the C3H3 + C2H2 reaction across a range of temperatures, although the lifetime of l-C5H5 is relatively short for rearrangement to c-C5H5.

Compositional effects on PAH and soot formation in counterflow diffusion flames of gasoline surrogate fuels

Gasoline surrogate fuels are widely used to understand the fundamental combustion properties of complex refinery gasoline fuels. In this study, the compositional effects on polycyclic aromatic hydrocarbons (PAHs) and soot formation were investigated experimentally for gasoline surrogate mixtures comprising n-heptane, iso-octane, and toluene in counterflow diffusion flames. A comprehensive kinetic model for the gasoline surrogate mixtures was developed to accurately predict the fuel oxidation along with the formation of PAHs and soot in flames. This combined model was first tested against ignition delay times and laminar burning velocities data. The proposed model for the formation and growth of PAHs up to coronene (C24H12) was based on previous studies and was tested against existing and present new experimental data. Additionally, in the accompanied soot model, PAHs with sizes larger than (including) pyrene were used for the inception of soot particles, followed by particle coagulations and PAH condensation/chemical reactions on soot surfaces. The major pathways for the formation of PAHs were also identified for the surrogate mixtures. The model accurately captures the synergistic PAH formation characteristics observed experimentally for n-heptane/toluene and iso-octane/toluene binary mixtures. Furthermore, the present experimental and modeling results also elucidated different trends in the formation of larger PAHs and soot between binary n-heptane/iso-octane and ternary n-heptane/iso-octane/toluene mixtures. Propargyl radicals (C3H3) were shown to be important in the formation and growth of PAHs for n-heptane/iso-octane mixtures when the iso-octane concentration increased; however, reactions involving benzyl radicals (C6H5CH2) played a significant role in the formation of PAHs for n-heptane/iso-octane/toluene mixtures. These results indicated that the formation of PAHs and subsequently soot was strongly affected by the composition of gasoline surrogate mixtures.

Soot reduction effects of the addition of four butanol isomers on partially premixed flames of diesel surrogates

The four alcoholic isomers of butanol were added into T20 diesel surrogate (80% n-heptane and 20% toluene in volume) in co-flow partially premixed flames at volumetric fractions of 20% and 40% in order to investigate the effect of butanol addition on polycyclic aromatic hydrocarbons (PAHs) and soot formation. For excluding the influence of toluene, the flame of T16 (84% n-heptane and 16% toluene in volume) and T12 (88% n-heptane and 12% toluene in volume) were also investigated to compare 20% and 40% butanol blend-flames in the same content of toluene. Laser-induced fluorescence and laser-induced incandescence were used to probe the distributions and concentrations of PAHs and soot volume fraction. A detailed n-heptane-toluene-butanols-PAH kinetic model was constructed in order to clarify the chemical effects of the different butanol-blended fuels on PAH formation. The results show that the reduced toluene content (due to butanol addition) is the dominant factor for PAH and soot reduction, compared with the base fuel of T20. The different PAH formation for the tested butanol-blended fuels is attributed to the different reaction pathways of butanol isomers. The branched-carbon-chain butanols (tertiary butanol and isobutanol) tend to produce more propargyl radicals than those of straight-carbon-chain butanols (normal butanol and secondary butanol), thus the PAH formation is higher for the branched butanols. The soot volume fractions with tertiary butanol and isobutanol addition are even higher than that without an additive in the fuel, while the addition of normal butanol and second butanol can reduce soot volume fractions further caused by its oxygenated molecular structure compared with T16 and T12. The soot formation tendency can actually be sequenced by tertiary butanol>isobutanol>secondary butanol>normal butanol at both 20% and 40% blending ratios. The concentration of four-ring PAHs is proportional to soot volume fraction, which means that four-ring PAHs can be used as the indicator of soot formation.

Products of the Propargyl Self-Reaction at High Temperatures Investigated by IR/UV Ion Dip Spectroscopy.

The propargyl radical is considered to be of key importance in the formation of the first aromatic ring in combustion processes. Here we study the bimolecular (self-) reactions of propargyl in a high-temperature pyrolysis flow reactor. The aromatic reaction products are identified by IR/UV ion dip spectroscopy, using the free electron laser FELIX as mid-infrared source. This technique combines mass selectivity with structural sensitivity. We identified several aromatic reaction products based on their infrared spectra, among them benzene, naphthalene, phenanthrene, indene, biphenyl, and surprisingly a number of aromatic compounds with acetylenic (ethynyl) side chains. The observation of benzene confirms that propargyl is involved in the formation of the first aromatic ring. The observation of compounds with acetylenic side chains shows that, in addition to a propargyl- and phenyl-based mechanism, the HACA (hydrogen abstraction C2H2 addition) mechanism of polycyclic aromatic hydrocarbons formation is present, although no acetylene was used as a reactant. On the basis of the experimental results we suggest a mechanism that connects the two pathways.

Experimental and Kinetic Modeling Study of 2-Methylfuran Pyrolysis at Low and Atmospheric Pressures

The pyrolysis of 2-methylfuran (MF) was studied from 900 to 1530 K in a flow reactor at 30 and 760 Torr. Synchrotron vacuum ultraviolet photoionization mass spectrometry and gas chromatography were used for identification and mole fraction measurements of pyrolysis products, especially free radicals and aromatics. Specific products were observed for the two main unimolecular decomposition pathways of MF, such as propargyl radical, methyl radical, 1-butyne, and carbon monoxide. A previous kinetic model of MF was updated on the basis of recent theoretical and modeling progresses, especially for the aromatic formation sub-mechanism. The updated model was validated by the new pyrolysis data. Kinetic analyses including rate of production analysis, and sensitivity analysis were used to provide insight into the pyrolysis chemistry of MF, especially the decomposition of MF and aromatic formation. The pyrolysis of MF was found with the kinetic characteristics of both furan pyrolysis and 2,5-dimethylfuran (DMF) pyr...

Experimental and numerical investigation of low-pressure laminar premixed synthetic natural gas flames in rich conditions

The present work concerns the study of rich laminar premixed CH4/C2H6/C3H8/O2/N2 flames operating at two equivalence ratios (ϕ=1.66 and 2.05) and low pressure (80Torr). In the case of the flame ϕ=2.05, the influence of pressure was studied between 80 and 300Torr. Mole fraction of reactants, stable intermediate and combustion products have been obtained using a quartz microprobe coupled to gas chromatography, mass spectrometry and infrared spectroscopy technique analysis. Temperature profiles measured with a coated thermocouple were corrected from radiative heat losses by electrical compensation method. A detailed chemical kinetic mechanism has been developed. Globally the main experimental observations are well captured by the present mechanism, especially the effect of the equivalence ratio and pressure on the chemical species distribution. The proposed mechanism has been also tested to predict detailed and global data in other experimental conditions (ignition delay times, burning velocities, and jet stirred reactor). Reactions paths analyses have been carried out to identify the main reactions routes governing natural gas combustion in rich conditions. Both effect of pressure and initial composition on C2 (ethylene, acetylene), C3 (allene, propyne) and C4 (butadiene, butyne) hydrocarbon species known as first ring precursors, have been examined. It was observed that self propargyl radicals is the main reaction route determining benzene formation in natural gas combustion in rich conditions.

Acquiring and Exploiting Persistency of Propargyl Radicals: Novel Paradigms

Three complementary methods for altering an intrinsic nature of propargyl radicals, from transient to persistent, were developed by fine-tuning the bulkiness and degree of substitution around the secondary and tertiary propargylic carbons, as well as by sterically enhancing a π-bonded Co2(CO)6 metal core. The latter was employed, as a mechanistic tool, for precluding an acetylene–allene rearrangement, stabilizing propargyl cations, and creating a steric hindrance that could provide for said transition from transient to persistent propargyl radicals. A window of opportunities was identified wherein the steric bulkiness in propargyl radicals remains below the “persistency threshold”, providing good to excellent stereoselectivities in radical dimerization reactions (d,l 62–100%). Along with the persistency threshold for tertiary propargyl radicals (278.2 A3), two different thresholds for persistency in secondary propargyl radicals were established—306.5 and 576.0 A3—dependent upon the molecular architecture ...

Experimental and kinetic modeling study of laminar coflow diffusion methane flames doped with iso-butanol

In this work, laminar coflow diffusion flames fueled with methane/iso-butanol were investigated with synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). Mole fractions of C2–C16 flame species, including small hydrocarbons, oxygenates and aromatics were measured along the flame centerline. The enhancement in the formation of aromatics was observed through the increment of the iso-butanol doping ratio (1.95% and 3.90% in two flames) in the inlet fuel gas mixture. A detailed kinetic model was developed from previous models to help understand the experimental findings. According to rate of production analysis in laminar coflow diffusion flames, unimolecular decomposition and H abstraction reactions provide equivalent contributions to the consumption of iso-butanol. Compared to the coflow flames doped with other butanol isomers with the identical condition, the water elimination reaction of iso-butanol has the lowest contribution to fuel consumption. Two reaction pathways provide major contribution to the formation of propargyl radical, i.e. iC4H9OH→iC3H7→C3H6→aC3H5→aC3H4→C3H3 and iC4H9OH→βC4H8OH→iC4H8→iC4H7→aC3H4→C3H3. Propargyl is concluded as the key precursor for aromatics, while phenyl and benzyl radicals are the main PAH precursors. Finally, based on the studies of laminar coflow flames fueled with butanol isomers, the sooting tendency of butanol isomers relates strictly to the efficiency of the propargyl formation pathways in fuel decomposition.

Allene and Propyne Combustion in Premixed Flames: A Detailed Kinetic Modeling Study

ABSTRACTThe combustion chemistry of allene and propyne is critical for the breakdown of higher hydrocarbon fuels and for molecular growth processes. Allene and propyne consumption reactions are primary sources of the key propargyl and allyl radicals, which are closely linked to benzene, polyaromatic hydrocarbons (PAHs), and soot formation paths. However, uncertainties exist concerning aspects of the C3H4 isomers’ chemistry. The article is part of an on-going effort aiming towards the optimization of a comprehensive kinetic mechanism for the high temperature combustion of small (C1–C6) hydrocarbon species. The mechanism is here validated against species data from stoichiometric and fuel-rich laminar premixed allene and propyne flames with considerable success. A critical evaluation of C3H4 consumption pathways has been carried out and the dynamics of benzene formation and destruction are discussed.

A study of the electronic structure and properties of the propargyl radical

By means of B3LYP/6-311++G(3df,3pd) the electron density distribution in the propargyl radical CH2CCH is obtained. Within the Quantum Theory of Atoms in Molecules the phenomenon of conjugation and the spin density distribution of the unpaired electron in CH2CCH are studied at the qualitative level. Characteristics of the electronic structure of CH2CCH and its parent molecules CH3–C≡CH and CH2=C=CH2 are compared. With the use of the rigid rotator-anharmonic oscillator model the thermodynamic properties of the propargyl radical and enthalpies of bond cleavage in propyne and allene are calculated in the temperature range 298-1500 K. The relationship between the electronic and thermodynamic properties of CH2CCH is considered and its conjugation energy is calculated.

Reaction between propargyl radical and 1,3-butadiene to form five to seven membered rings. Theoretical study

Propargyl radical addition to 1,3-butadiene seems to be a promising channel to form 5-, 6-, and 7-membered rings. These are important steps in the growth of polycyclic aromatic hydrocarbons and soot platelets. The reaction mechanism, involving 97 intermediates and 115 transition structures, was studied by CBS-QB3 method (reported here) and density functional theory. All these structures were included in the subsequent RRKM study at different combustion pressures (P=30–0.01atm) and temperatures (T=1200–2100K). At P=30atm, open-chain products dominate in the whole range of temperatures. The importance of 5- and 6-membered rings rises with T, reaching a maximum in the T range 1500–1800K. A more modest yield in 7-rings is present at T=1500K. At P=1atm, in the range 1200–1500K, the yield in 5-and 6-rings dominate. 5- and 6-rings yields are about 41% at 1200K (CBS-QB3 data). At P=0.1 atm, 6-rings become the main products a 1000K (35%), and then they decrease to 12% (2100K) and 5-rings rise up to 44% (1200K), and then decrease to 14% (2100K). Open-chains are the main products at T<1000K and T>1500K. Then, at P=0.01 atm, open-chain products are important below 900K and above 1500K,6-rings are main contributors between 900K and 1500K. 6-Rings reach a maximum yield of 47% (1200K) and 5-rings 44% (1200K) and 7-rings 17% (900K). The main products form through to H losses.