F:Flammable;
563-79-1Relevant academic research and scientific papers
Kinetics of the thermal isomerization of 1,1,2-trimethylcyclopropane
Lewis, David K.,Hughes, Steven V.,Miller, Justine D.,Schlier, Jessica,Wilkinson, Kevin A.,Wilkinson, Sara R.,Kalra, Bansi L.
, p. 475 - 482 (2006)
The Arrhenius parameters for the gas phase, unimolecular structural isomerizations of 1,1,2-trimethylcyclopropane to three isomeric methylpentenes and two dimethyl-butenes have been determined over a wide range of temperatures, 688-1124 K, using both static and shock tube reactors. For the overall loss of reactant. Ea =63.7 (±0.5) kcal/mol and log10 A= 15.28 (±0.12). These values are higher by 2.6 kcal/mol and 0.7-0.8 than previously reported from experimental work or predicted from thermochemical calculations. Ea for the formation of trans-4-methyl-2-pentene is 1.5 kcal/mol higher than Ea for the formation of the cis isomer, which is identical to the Ea difference previously reported for the formation of trans- and cis-2-butene from methylcyclopropane. Substitution of methyl groups for hydrogen atoms on the cyclopropane ring is expected to weaken the C - C ring bonds, and it has been reported previously that activation energies for structural isomerizations of methylcyclo-propanes do decrease substantially over the series cyclopropane > methylcyclopropane > 1, 1-or 1,2-dimethylcyclopropane. However, the present study shows that the trend does not continue beyond dimethylcyclopropane isomerization. Besides reductions in C - C bond energy, steric interactions may be increasingly important in determining the energy surface and conformational restrictions near the transition state in isomerizations of the more highly substituted methylcyclopropanes.
[BO2]? as a Synthon for the Generation of Boron-Centered Carbamate and Carboxylate Isosteres
Hill, Michael S.,Mahon, Mary F.,McMullin, Claire L.,Pécharman, Anne-Frédérique
, p. 13628 - 13632 (2020)
Oxoborane carbamate and carboxylate analogues result from the in situ trapping of [BO2]? produced by elimination of 2,3-dimethyl-2-butene from a pinacolatoboryl anion.
Cyclopentadienyl(allyl) (butadiene)hafnium compounds. Synthesis, crystal structure, and dynamics of cyclopentadienyl(1,2,3-trimethylallyl)(1,2-dimethylbutadiene)-hafnium and cyclopentadienyl(1,1,2-trimethylallyl)-(2,3-dimethylbutadiene)hafnium
Prins, Thomas J.,Hauger, Bryan E.,Vance, Peter J.,Wemple, Michael E.,Kort, David A.,O'Brien, Jonathan P.,Silver, Michael E.,Huffman, John C.
, p. 979 - 985 (1991)
The reaction of CpHfCl3·2THF with 2 equiv of (1,2,3-Me3allyl)MgBr or (1,1,2-Me3allyl)MgBr yields Cp(1,2,3-Me3allyl)(1,2-Me2butadiene)Hf (3) or Cp(1,1,2-Me3allyl)(2,3-Me2butadiene)Hf (4). X-ray crystallography of 3 shows that both the allyl and butadiene ligands assume a prone orientation with respect to Cp. For 3: cell constants a = 15.109 (5), b = 7.150 (2), c = 15.587 (6) A?, β = 115.41 (1)°; space group P21/c; R = 0.0305, Rw = 0.0347. Variable-temperature 1H NMR studies indicate that compound 3 is static on the NMR time scale whereas 4 exists in two isomeric forms and undergoes three separate dynamic processes involving η3-η1 isomerization at the unsubstituted and substituted ends of the allyl ligand [ΔG? = 39.4 ± 1.0 kJ/mol and 73.4 ± 1.0 kJ/mol, respectively] and butadiene flip [ΔG?(avg) = 49.8 ± 1.0 kJ/mol].
Temperature Effect on Ion-Molecule Reaction of Hydrogen Transfer in γ-Irradiated 2,3-Dimehylbutane at 4 K and 77 K As Studied by Electron Spin Resonance Spectroscopy
Miyazaki, Tetsuo,Tsuruta, Haruyuki,Fujitani, Yoshiteru,Fueki, Kenji
, p. 970 - 972 (1982)
Drastic temperature effects on an ion-molecule reaction of H2 transfer in solid hydrocarbon systems were studied at 4 and 77 K by ESR spectroscopy.When a 2,3-dimethylbutane (DMB)-SF6 (0.55 mol percent)-i-C4H8 (0.55 mol percent) mixture is irradiated at 4 K, the DMB(+) ion in addition to the DMB radical is formed.The tetramethylethylene (TME) cation is produced by warming the irradiated DMB-SF6-i-C4H8 mixture from 4 to 77 K.The formation of the TME(+) ion observed at 77 K is interpreted in terms of the H2 transfer reaction between the DMB(+) ion and i-C4H8.This ion-molecule reaction is completely suppressed at 4 K.The suppression of the ion-molecule reaction is explained by failure of the formation of a reaction complex in the rigid matrix at 4 K.The amounts of TME(+) ions in the DMB-SF6-i-C4H8 mixture increase gradually upon storage of the irradiated mixture at 77 K.This result indicates that the transfer reaction occurs slowly at 77 K.
Pulse Radiolysis and E.S.R. Evidence for the Formation of an Alkene Radical Cation in Aqueous Solution
Asmus, Klaus-Dieter,Williams, Peter S.,Gilbert, Bruce C.,Winter, Jeremy N.
, p. 208 - 210 (1987)
Direct pulse radiolysis evidence, complemented by e.s.r. experiments, establishes that the radical cation Me2C=-C.Me2 (λmax ca. 290 nm) is formed by acid-catalysed elimination of OH- from .CMe2CMe2OH; the radica
Isomerization of Olefin Radical Cations in ZSM-5 Zeolites
Werst, D. W.,Tartakovsky, E. E.,Picos, E. A.,Trifunac, A. D.
, p. 10249 - 10257 (1994)
Variable-temperature EPR was used to investigate reactions of olefin radical cations generated radiolytically in nonacidic and acidic ZSM-5 zeolites.The olefin radical cations undergo isomerization reactions even at 4K.Radical cation reactions are presumably driven by the exothermicity of charge transfer, which is not efficiently quenched by the vibrational modes of the zeolite lattice.The observation of H-addition type radicals indicates Bronsted acid-catalyzed rearrangements prior to irradiation on the more acidic zeolites.
Radiolytic Generation of Organic Radical Cations in Zeolite Na-Y
Qin, X.-Z.,Trifunac, A. D.
, p. 4751 - 4754 (1990)
Several examples of radiolytically generated organic radical cations in zeolite Na-Y are illustrated.EPR studies of organic radical cations can be carried out in a wide range of temperatures up to room temperature.In every case, monomeric radical cations were observed.Comparison to previous work in freon and xenon matrices is made, illustrating that in the zeolite Na-Y there is considerably weaker radical cation-host interaction.A mechanism of radiolytic generation of radical cations in zeolite Na-Y is proposed.
Photocatalytic Oxidative [2+2] Cycloelimination Reactions with Flavinium Salts: Mechanistic Study and Influence of the Catalyst Structure
Hartman, Tomá?,Reisnerová, Martina,Chudoba, Josef,Svobodová, Eva,Archipowa, Nataliya,Kutta, Roger Jan,Cibulka, Radek
, p. 373 - 386 (2021/02/01)
Flavinium salts are frequently used in organocatalysis but their application in photoredox catalysis has not been systematically investigated to date. We synthesized a series of 5-ethyl-1,3-dimethylalloxazinium salts with different substituents in the positions 7 and 8 and investigated their application in light-dependent oxidative cycloelimination of cyclobutanes. Detailed mechanistic investigations with a coumarin dimer as a model substrate reveal that the reaction preferentially occurs via the triplet-born radical pair after electron transfer from the substrate to the triplet state of an alloxazinium salt. The very photostable 7,8-dimethoxy derivative is a superior catalyst with a sufficiently high oxidation power (E=2.26 V) allowing the conversion of various cyclobutanes (with Eox up to 2.05 V) in high yields. Even compounds such as all-trans dimethyl 3,4-bis(4-methoxyphenyl)cyclobutane-1,2-dicarboxylate can be converted, whose opening requires a high activation energy due to a missing pre-activation caused by bulky adjacent substituents in cis-position.
Highly Active Superbulky Alkaline Earth Metal Amide Catalysts for Hydrogenation of Challenging Alkenes and Aromatic Rings
Eyselein, Jonathan,F?rber, Christian,Grams, Samuel,Harder, Sjoerd,Knüpfer, Christian,Langer, Jens,Martin, Johannes,Thum, Katharina,Wiesinger, Michael
supporting information, p. 9102 - 9112 (2020/03/30)
Two series of bulky alkaline earth (Ae) metal amide complexes have been prepared: Ae[N(TRIP)2]2 (1-Ae) and Ae[N(TRIP)(DIPP)]2 (2-Ae) (Ae=Mg, Ca, Sr, Ba; TRIP=SiiPr3, DIPP=2,6-diisopropylphenyl). While monomeric 1-Ca was already known, the new complexes have been structurally characterized. Monomers 1-Ae are highly linear while the monomers 2-Ae are slightly bent. The bulkier amide complexes 1-Ae are by far the most active catalysts in alkene hydrogenation with activities increasing from Mg to Ba. Catalyst 1-Ba can reduce internal alkenes like cyclohexene or 3-hexene and highly challenging substrates like 1-Me-cyclohexene or tetraphenylethylene. It is also active in arene hydrogenation reducing anthracene and naphthalene (even when substituted with an alkyl) as well as biphenyl. Benzene could be reduced to cyclohexane but full conversion was not reached. The first step in catalytic hydrogenation is formation of an (amide)AeH species, which can form larger aggregates. Increasing the bulk of the amide ligand decreases aggregate size but it is unclear what the true catalyst(s) is (are). DFT calculations suggest that amide bulk also has a noticeable influence on the thermodynamics for formation of the (amide)AeH species. Complex 1-Ba is currently the most powerful Ae metal hydrogenation catalyst. Due to tremendously increased activities in comparison to those of previously reported catalysts, the substrate scope in hydrogenation catalysis could be extended to challenging multi-substituted unactivated alkenes and even to arenes among which benzene.
Spiro[1,2]oxaphosphetanes of nonstabilized and semistabilized phosphorus ylide derivatives: Synthesis and kinetic and computational study of their thermolysis
López, Jesús García,Sansores Peraza, Pablo M.,Iglesias, María José,Roces, Laura,García-Granda, Santiago,Ortiz, Fernando López
supporting information, p. 14570 - 14591 (2020/11/20)
A series of tri- and tetrasubstituted spiro-oxaphosphetanes stabilized by ortho-benzamide (oBA) and N-methyl ortho-benzamide (MoBA) ligands have been synthesized by the reaction of Cα,Cortho-dilithiated phosphazenes with aldehydes and ketones. They include enantiopure products and the first example of an isolated oxaphosphetane having a phenyl substituent at C3 of the ring. Kinetic studies of their thermal decomposition showed that the process takes place irreversibly through a polar transition state (ρ = -0.22) under the influence of electronic, [1,2], [1,3] steric, and solvent effects, with C3/P-[1,2] interactions as the largest contribution to ΔG of olefination. Inversion of the phosphorus configuration through stereomutation has been observed in a number of cases. DFT calculations showed that oBA derivatives olefinated through the isolated (N, O)(Ph, C6H4, C) oxaphosphetanes (Channel A), whereas MoBA compounds decomposed faster via the isomer (C6H4, O)(C, N, Ph) formed by P-stereomutation involving a MB2 permutational mechanism (Channel B). The energy barrier of P-isomerization is lower than that of olefination. Fragmentation takes place in a concerted asynchronous reaction. The thermal stability of oxaphosphetanes is determined by strong C3/P-[1,2] interactions destabilizing the transition state of olefination. The effect of charge distribution and C3/C4-[1,2] and C4/P-[1,3] steric and solvent interactions on ΔG was also evaluated.
