82252-88-8Relevant articles and documents
Electron Paramagnetic Resonance Study of Radical Formation from Cyclopentene and Dimethylacetylene following Adsorption onto H-Mordenite
Rhodes, Christopher J.
, p. 3179 - 3184 (1991)
Following adsorption of cyclopentene onto H-mordenite at low temperatures an EPR spectrum at 77 K which can be unequivocally assigned to the radical cation of 1,2,3,4,5,6,7,8-octahydronaphthalene (9-octalin), since it is identical with the spectrum recorded from an authentic sample of 9-octalin following γ-irradiation in a CFCl3 matrix.This radical shows an interesting dynamic behaviour in terms of a concerted inversion of both rings that modulates the pseudoaxial and pseudoequatorial couplings.On initial adsorption at 195 K the activation energy associated with this process is 14.4 kJ mol-1 (actually less than that measured in solution by ODMR) but which surprisingly increases to 28.3 kJ mol-1 on warming the sample to 295 K.This is interpreted in terms of radicals located at differing adsorption sites.A similar adsorption study of dimethylacetylene on this zeolite led, at 150 K, to the detection of a spectrum with an odd number of broadish lines and a spacing of ca. 10 G which we attribute to the formation of the tetramethylcyclobutadiene radical cation.On heating to 350 K, the spectrum of the hexamethylbenzene radical cation was observed.A comparative study of these compounds in freon matrices at varying concentrations was also made in order to probe the chemical properties of their radical cations by an authentic and independent method.
Crossed-beam reaction of carbon atoms with hydrocarbon molecules. IV. Chemical dynamics of methylpropargyl radical formation, C4H5, from reaction of C(3Pj) with propylene, C3H6 (X1A′)
Kaiser,Stranges,Bevsek,Lee,Suits
, p. 4945 - 4953 (1996)
The reaction between ground state carbon atoms and propylene, C3H6, was studied at average collision energies of 23.3 and 45.0 kJ mol-1 using the crossed molecular beam technique. Product angular distributions and time-of-flight spectra of C4H5 at m/e=53 were recorded. Forward-convolution fitting of the data yields a maximum energy release as well as angular distributions consistent with the formation of methylpropargyl radicals. Reaction dynamics inferred from the experimental results suggest that the reaction proceeds on the lowest 3A surface via an initial addition of the carbon atom to the π-orbital to form a triplet methylcyclopropylidene collision complex followed by ring opening to triplet 1,2-butadiene. Within 0.3-0.6 ps, 1,2-butadiene decomposes through carbon-hydrogen bond rupture to atomic hydrogen and methylpropargyl radicals. The explicit identification of C4H5 under single collision conditions represents a further example of a carbon-hydrogen exchange in reactions of ground state carbon with unsaturated hydrocarbons. This versatile machine represents an alternative pathway to build up unsaturated hydrocarbon chains in combustion processes, chemical vapor deposition, and in the interstellar medium.
Factors influencing C-ON bond homolysis in alkoxyamines: Unexpected behavior of SG1 (N-(2-methyl-2-propyl)-N-(1-diethylphosphono-2,2-dimethylpropyl) -N-oxyl)-based alkoxyamines
Bertin, Denis,Gigmes, Didier,Le Mercier, Christophe,Marque, Sylvain R. A.,Tordo, Paul
, p. 4925 - 4930 (2007/10/03)
Alkoxyamines and persistent nitroxides are important regulators of nitroxide-mediated radical polymerization (NMP). Since the polymerization time decreases with the increasing equilibrium constant K (kdk c), i.e., the increasing rate constant kd of the homolysis of the C-ON bond between the polymer chain and the nitroxide moiety, the factors influencing the cleavage rate constants are of considerable interest. SG1-based alkoxyamines have turned out to be the most potent alkoxyamine family to use for NMP of various monomers. Therefore, it is of high interest to determine the factors which make SG1 derivatives better regulators than TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl) derivatives. Contrary to what we had observed with TEMPO derivatives, we observed two relationships for the plot Ea vs BDE(C-H), one for the nonpolar released alkyl radicals (E a (kJ/mol) = -133.0 + 0.72BDE) and the other one for the polar released alkyl radicals (Ea (kJ/mol) = -137.0 + 0.69BDE). However, for both families (SG1 and TEMPO derivatives), the rate constants kd of the C-ON bond homolysis were correlated to the cleavage temperature T c (log(kd(s-1)) = 1.51 -0.058Tc). Such correlations should help to design new alkoxyamines to use as regulators and to improve the tuning of NMP experiments.
Photofragment translational spectroscopy of 1,2-butadiene at 193 nm
Robinson, Jason C.,Sun, Weizhong,Harris, Sean A.,Qi, Fei,Neumark, Daniel M.
, p. 8359 - 8365 (2007/10/03)
The dissociation dynamics of 1,2-butadiene at 193 nm were analyzed by photofragment translational spectroscopy. Tunable vacuum ultraviolet (VUV) synchrotron radiation at the Advanced Light Source (ALS) was used for ionization of scattered photoproducts. I
IR-Chemiluminescence from the Reactions of Atomic Fluorine with Ethyne and Butyne-2
Schwanke, U.,Heydtmann, H.
, p. 1395 - 1400 (2007/10/02)
The reactions F + C2H2 and F + C4H6 (2-butyne) were studied in a low pressure flow system using the IR-chemiluminescence technique.The vibrational-rotational state distributions for the product molecule HF were determined for various conditions.For F + C2H2 only secondary reactions can lead to vibrational excitation of HF; with an excess of F-atoms HF (v 1:N2:N3:N4 = 26:36:32:7.With an excess of F atoms v = 5 and v = 6 are populated.The possible secondary steps are discussed on the basis of our observations.
Electron Delocalisation and Stabilisation in Substituted Amino- and Hydroxypropynyl Radicals
MacInnes, Iain,Walton, John C.
, p. 1077 - 1082 (2007/10/02)
A series of aminopropynes, RCCCH2NH2 (R = H, Me, t-Bu, Me3Si), RCCCH2N(SiMe3)2, and hydroxypropynes RCCCH2OH (R = H, Me, t-Bu, Me3Si, CF3, and EtO2C), were prepared and the corresponding α-aminopropynyl and α-hydroxypropynyl radicals were examined by e.s.r. spectroscopy.For the first series, the C-N bond rotation barriers were determined from the exchange broadening in the spectra and hence radical stabilization energies were estimated.The spin distribution in these series indicated an extra delocalisation in radicals with captodative substitution.
Kinetics of Decomposition and Interconversion of 3-Methylbut-1-yne and 3-Methylbuta-1,2-diene. Resonance Stabilization Energies of Propargylic Radicals
Nguyen, Tam T.,King, Keith D.
, p. 3130 - 3136 (2007/10/02)
The thermal unimolecular reactions of 3-methylbut-1-yne (MBT) and 3-methylbuta-1,2-diene (MBTD) have been studied over the temperature range 940-1222 K by using the technique of very low-pressure pyrolysis (VLPP).Both compounds decompose via C3-C4 bond fission producing the resonance-stabilized radicals, 1-methylpropargyl from MBT and 1-methylallenyl from MBTD.In addition, interconversion between the two reactants takes place via structural isomerization.RRKM calculations, incorporating competing pathways and a temperature-dependent gas/wall collision efficiency, show that the experimental rate constants are consistent with the following high-pressure specific rate expressions at 1100K : log(k1/s-1) = (16.3 +/- 0.3) - (71.6 +/- 1.0)/Τ for bond fission and log(k2/s-1) = (13.2 +/- 0.6) - (60.5 +/- 1.0)/Τ for isomerization for MBT, log(k3/s-1) = (16.3 +/- 0.3) - (75.3 +/- 1.0)/Τ for bond fission and log(k4/s-1) = (13.2 +/- 0.6) - (63.8 +/- 1.0)/Τ for isomerization for MBTD, where Τ = 2.303RT kcal/mol.The A factor for bond fission was assigned from the results of recent shock-stube studies of related alkynes, and the A factor for isomerization was adopted from that previously reported for the analogous allene propyne interconversion.The results lead to ΔH0f300 = 72.4, DH0300 = 85.0, ΔH0f300 = 74.3, and DH0300 = 91.4 kcal/mol.The resonance stabilization energies are 10.0 +/- 2.2 and 7.8 +/- 2.2 kcal/mol for the 1-methylpropargyl and 1-methylallenyl radicals, respectively, in reasonable agreement with previous results for other propargylic radicals.The activation energy for the isomerization MBTD -> MBT is similar to that previously reported for the conversion of allene to propyne, and the equilibrium constants for the interconversion MBT MBTD calculated from therate date show good agreement with the values estimated from thermodynamic data over the experimental temperature range.
