- Photodissociation of Tetramethylene Sulfoxide at 193 and 248 nm in the Gas Phase
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The 193 and 248 nm photodissociation of tetramethylene sulfoxide (TMSO) in the gas phase has been investigated by using laser spectroscopic techniques.The vibrational state distributions of the nascent SO(X3Σ-) photofragment following irradiation at 193 and 248 nm have been measured by using laser-induced fluorescence (LIF) spectroscopy on the B3Σ- - X3Σ- transition.These vibrational state distributions can be characterized as Boltzmann with vibrational temperatures of 1250 +/- 60 and 1220 +/- 60 K for the 193 and 248 nm photolyses, respectively.Assuming that the SO photofragment is produced in concert with a 1,4-tetramethylene diradical, the vibrational state distribution obtained in the 193 nm photolysis agrees well with an energy disposal model, in which the full reaction exoergicity is statistically partitioned among all the products' degrees of freedom.The quantum yield for SO(X3Σ-) production at 193 nm, Φ193SO = 0.47 +/- 0.20, has been obtained by comparison with SO2 photolysis.For the 248 nm photodissociation, the experimentally obtained vibrational state distribution can be best described by a variant statistical model assuming three-body fragmentation; i.e. the products are an SO fragment and two ethylene molecules.The quantum yield for SO(X3Σ-) production at 248 nm is Φ248SO = 0.44 +/- 0.19.The OH photofragment has been detected during both the 193 and 248 nm photolyses of TMSO.The rotational state distributions of the OH(X2Π, ν'' = 0) fragment have been determined by LIF spectroscopy using the A2Σ-X2Π transition.The hydroxyl rotational temperatures can be characterized as 600 +/- 50 and 510 +/- 40 K following photolysis of TMSO at 193 and 248 nm, respectively.Mechanisms for the production of both SO and OH are discussed.
- Wu, Fei,Chen, Xirong,Weiner, Brad R.
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Read Online
- The Photocycloaddition of Acetylacetone with Naphthols and their Methyl Ethers
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Whereas irradiation of a mixture of a naphthol (or its methyl ether) and acetylacetone with excitation of the naphthol component leads to no reaction, irradiation of a similar mixture with excitation of the acetylacetone component leads to its cycloaddition to the naphthalene derivative to give a cyclobutane as the primary photoproduct.
- Chow, Yuan L.,Buono-Core, Gonzalo E.,Liu, Xiao-Yun,Itoh, Kuniaki,Qian, Ping
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Read Online
- Exploring C(sp3)–C(sp3) reductive elimination from an isolable iron metallacycle
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A six-coordinate iron metallacyclopentane, (phen)2Fe(CH2)4, supported by two 1,10-phenanthroline (phen) ligands, has been synthesized and structurally and spectroscopically characterized. The complex is diamagnetic and an idealized octahedral geometry was observed in the solid state. The electronic structure of (phen)2Fe(CH2)4 was determined by a combination of X-ray diffraction, M?ssbauer spectroscopy, and DFT analyses and is best described as a low-spin Fe(III) center antiferromagnetically coupled to a radical anion delocalized equally over both phen ligands. The reactivity of (phen)2Fe(CH2)4 under different conditions was explored. Thermolysis or photolysis promoted elimination reactions and mixtures of isomeric butenes and butane were observed. Reactions of (phen)2Fe(CH2)4 with ethylene and isoprene yielded 3% and 11% of reductive elimination product cyclobutane, respectively, along with butane and butene isomers. Addition of π-accepting ligands such as carbon monoxide, maleic anhydride, or 1,4-benzoquinone to (phen)2Fe(CH2)4 promoted C(sp3)-C(sp3) reductive elimination as judged by high selectivity for cyclobutane formation. Two electron oxidation of (phen)2Fe(CH2)4 with two equivalents of ferrocenium tetraphenylborate also exclusively yielded cyclobutane in 95% yield. The electronic structure and reactivity of related bis(bipyridine) iron dialkyl compounds previously isolated by Kochi and co-workers were also revisited and their electronic structures revised based on structural, spectroscopic and computational data.
- Joannou, Matthew V.,Darmon, Jonathan M.,Bezdek, Máté J.,Chirik, Paul J.
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p. 308 - 317
(2019/01/04)
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- Palladium-Catalyzed, Norbornene-Mediated, ortho-Amination ipso-Amidation: Sequential C-N Bond Formation
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A palladium-catalyzed, norbornene-mediated ortho- and ipso-C-N bond-forming Catellani reaction is reported. This reaction proceeds through a sequential intermolecular amination followed by intramolecular cyclization of a tethered amide. The products, ortho-aminated dihydroquinolinones, were generated in moderate to good yields and are present in bioactive molecules. This work highlights the challenge of competing intra- vs intermolecular palladium-catalyzed processes.
- Whyte, Andrew,Olson, Maxwell E.,Lautens, Mark
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supporting information
p. 345 - 348
(2018/01/27)
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- Inter-conversion of light olefins on ZSM-5 in catalytic naphtha cracking condition
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The inter-conversion of light olefins over four types of HZSM-5 based catalysts under cracking conditions was investigated systematically and various methods including XRD, Ar adsorption-desorption, NH3-TPD, 27Al and 31P MAS-NMR were used to characterize the effects of P modification and steaming on ZSM-5. Regardless the types of catalyst, the same behaviors of light olefin inter-conversion were observed only depending on conversion of light olefins. Also, the conversion and selectivity were not influenced by the presence of hydrogen, suggesting that light paraffins were mainly produced from hydrogen transfer during cracking rather than hydrogenation of light olefins. It can be suggested that the inter-conversion of light olefins occurs through oligomerization of light olefins and then re-cracking of the oligomerized products. To guarantee high light olefin yield in catalytic naphtha cracking, it is strongly required to suppress oligomerization of light olefins during catalytic cracking.
- Liu, Dan,Choi, Won Choon,Kang, Na Young,Lee, You Jin,Park, Hun Soo,Shin, Chae-Ho,Park, Yong-Ki
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- Accuracy of calculations of heats of reduction/hydrogenation: Application to some small ring systems
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The enthalpies of reduction of carbonyl compounds and hydrogenation of alkenes have been calculated at the HF, B3LYP, M06, MP2, G3, G4, CBS-QB3, CBS-APNO, and W1BD levels and, in the case of the first four methods, using a variety of basis sets up to aug-cc-pVTZ. The results are compared with the available experimental data, and it is found that the compound methods are generally more satisfactory than the others. Large basis sets are usually needed in order to reproduce experiments. Some C-C bond hydrogenolysis reactions also have been examined including those of bicycloalkanes and propellanes. In addition, the dimerization of the remarkably strained bicyclo[2.2.0]hex(1,4)ene was studied. The reaction forming a pentacyclic propellane was calculated to have ΔH = -57 kcal/mol, and the cleavage of the propellane to give a diene had ΔH = -71 kcal/mol. The strain energies of these compounds were estimated.
- Wiberg, Kenneth B.
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p. 10393 - 10398
(2013/01/15)
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- Total synthesis and revised structure of biyouyanagin A
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(Chemical Equation Presented) It all adds up: A 12-step total synthesis of biyouyanagin A, an inhibitor of HIV replication, has revealed its structure, rendered it available for biological investigations, and allows the synthesis of analogues. The convergent synthesis involves two cascade sequences and a remarkably selective [2+2] cycloaddition reaction to forge the cyclobutane ring of the target molecule in the ultimate step.
- Nicolaou,Sarlah, David,Shaw, David M.
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p. 4708 - 4711
(2008/02/10)
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- Flash vacuum pyrolysis over magnesium. Part 1 - Pyrolysis of benzylic, other aryl/alkyl and aliphatic halides
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Flash vacuum pyrolysis over a bed of freshly sublimed magnesium on glass wool results in efficient coupling of benzyl halides to give the corresponding bibenzyls. Where an ortho halogen substituent is present further dehalogenation gives some dihydroanthracene and anthracene. Efficient coupling is also observed for halomethylnaphthalenes and halodiphenylmethanes while chlorotriphenylmethane gives 4,4′-bis(diphenylmethyl)biphenyl. By using α,α′-dihalo-o-xylenes, benzocyclobutenes are obtained in good yield, while the isomeric α,α′-dihalo-p-xylenes give a range of high thermal stability polymers by polymerisation of the initially formed p-xylylenes. Other haloalkylbenzenes undergo largely dehydrohalogenation where this is possible, in some cases resulting in cyclisation. Deoxygenation is also observed with haloalkyl phenyl ketones to give phenylalkynes as well as other products. With simple alkyl halides there is efficient elimination of HCl or HBr to give alkenes. For aliphatic dihalides this also occurs to give dienes but there is also cyclisation to give cycloalkanes and dehalogenation with hydrogen atom transfer to give alkenes in some cases. For 5-bromopent-1-ene the products are those expected from a radical pathway but for 6-bromohex-1-ene they are clearly not. For 2,2-dichloropropane and 1,1-dichloropropane elimination of HCl occurs but for 1,1-dichlorobutane, -pentane and -hexane partial hydrolysis followed by elimination of HCl gives E, E-, E,Z- and Z,Z- isomers of the dialk-1-enyl ethers and fully assigned 13C NMR data are presented for these. With 6-chlorohex-1-yne and 7-chlorohept-1-yne there is cyclisation to give methylenecycloalkanes and -cycloalkynes. The behaviour of 1,2-dibromocyclohexane and 1,2-dichlorocyclooctane under these conditions is also examined. Various pieces of evidence are presented that suggest that these processes do not involve generation of free gas-phase radicals but rather surface-adsorbed organometallic species.
- Aitken, R. Alan,Hodgson, Philip K.G.,Morrison, John J.,Oyewale, Adebayo O.
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p. 402 - 415
(2007/10/03)
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- Tricyclic inhibitors of the GPIIb IIIa receptor
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A tricylic benzodiazepine derivative that acts as a nonpeptidyl platelet aggregation inhibitor is provided. This inhibitor potently inhibits fibrinogen binding to the GPIIb IIIa receptor and is provided in therapeutic compositions for the treatment of diseases for which blocking platelet aggregation is indicated. These nonpeptidyl inhibitors are provided in combination with thrombolytics and anticoagulants.
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- Tricyclic inhibitors of the vitronectin receptor
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A tricylic benzodiazepine derivative that acts as a nonpeptidyl platelet aggregation inhibitor is provided. This inhibitor potently inhibits fibrinogen binding to the GPIIb IIIa receptor and is provided in therapeutic compositions for the treatment of diseases for which blocking platelet aggregation is indicated. These nonpeptidyl inhibitors are provided in combination with thrombolytics and anticoagulants.
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- Tricyclic inhibitors of the GPIIb IIIa receptor
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A trycylic benzodiazepine derivative which acts as a nonpeptidyl platelet aggregation inhibitor is provided. This inhibitor potently inhibits fibrinogen binding to the GPIIb IIIa receptor and is provided in therapeutic compositions for the treatment of diseases for which blocking platelet aggregation is indicated. These nonpeptidyl inhibitors are provided in combination with thrombolytics and anticoagulants.
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- Quantitative determination of volatile products formed in electrolyses of organic compounds
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A straightforward and accurate procedure has been developed for the quantitation of volatile products that are formed from electrolyses of organic compounds. This methodology, which eliminates the need for external cold traps, utilizes an internal standard that is present in both the solution and gas phases of a gas-tight electrochemical cell. By sampling the gas and solution phases of the cell at the end of an electrolysis and by using gas chromatography to determine the quantities of the various volatile products in each phase with respect to the internal standard, one can ascertain the absolute yield of each product derived from the electrolysis of the starting material. In this paper, we present the theoretical background for this technique, including the formulation and use of experimentally measured gas chromatographic response factors, and we demonstrate the applicability of the approach for the quantitation of seven volatile products that are formed by the electrolytic reduction of 1,4-dibromobutane at a reticulated vitreous carbon cathode in dimethylformamide containing tetramethylammonium perchlorate. This method can be readily adapted to any compound whose electrolysis gives rise to volatile products.
- Pritts, Wayne A.,Vieira, Kenneth L.,Peters, Dennis G.
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p. 2145 - 2149
(2007/10/02)
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- Synthese von Cyclobutan durch Dehalogenierung von 1,4-Dihalogenbutanen mit Alkalimetalldaempfen. Zur Relation von radikalischen und metallorganischen Reaktionskanaelen
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Gasphase dehalogenation of 1,4-dichloro-, 1-chloro-4-bromo-, 1,4-dibromobutanes and 1,4-dibromopentane by Na/K vapors produces cyclobutane resp. methylcyclobutane with selectivities of 55.5, 46.7, 32.0 and 17 moles/100 moles resp..Side products of the reaction are ethylene and hydrogen, yields of which increase with increasing temperature and rising degree of substitution of chlorine by bromine.A mechanism is discussed in which the initiation step is the generation of halobutyl radicals of the type H2C*-(CH2)2-CH2X (X = Cl, Br) which are reacting further in two ways - by formation of tetramethylenediradical, splitting off the second halogen atom, or by the formation of the metallorganic compound 1-potassium-4-halogenobutane, which further cyclisizes to cyclobutane splitting off KX.Using some methods of theoretical chemistry such as quantumchemical calculations based on ab initio (STO-3G) and semiempirical (AM1) structures, on the relative energies of conformers of halogenobutylradicals and on models of the metallorganic intermediates, but also by conformation calculations of the content of rotation isomers of the intermediate formed, the correlation between the two reaction channels depending on the type of halogen was estimated.The calculations showed that only about 20 percent of cyclobutane are generated by the radical pathway.The high predominance of the metallorganic channel in the case of 1,4-dichlorobutane is caused by the high lifetime of chlorobutyl radicals in comparison with its bromoanalogues.
- Volnina, S. A.,Avakjan, V. G.,Guselnikov, L. E.,Yaya, A. Al
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p. 1061 - 1072
(2007/10/02)
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- The Gas-Phase Acidities of the Alkanes
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The gas-phase acidities of 15 simply alkanes have been determined in a flowing afterglow-selected ion flow tube (FA-SIFT) by a kinetic method in which alkyltrimethylsilanes are allowed to react with hydroxide ions to produce a mixture of trimethylsiloxide ions by loss of alkane and alkyldimethylsiloxide ions by loss of methane.The reaction is proposed to proceed by addition of hydroxide ion to the silane to form a pentacoordinate siliconate ion intermediate which decomposes through two transition states, one in which negative charge is placed on a methyl group and the other in which negative charge is placed on the alkyl group.The ratio of siloxide ions produced is proposed to be correlated to the relative basicity of the methyl and alkyl anions.The method is calibrated by making use of the known acidities of methane (ΔH0acid=416.6 kcal/mol) and benzene (ΔH0acid= 400.7 kcal/mol).In general, methyl substitution is found to stabilize alkyl anions in the gas phase except that the ethyl anion is found to be more basic that the methyl anion.By combining the gas-phase acidities with the bond dissociation energies, the electron affinities (EA) of the corresponding alkyl radicals can be calculated.Many simple alkyl radicals are found to have negative EA's.The results for the alkyl groups studied are as follows, where the first number is the ΔH 0acid (kcal/mol) of the corresponding alkane and the second number (in parentheses) is the EA (kcal/mol) of the alkyl radical: ethyl 420.1 (-6.4), isopropyl 419.4 (-9.5), cyclobutyl 417.4 (-7.5), cyclopentyl 416.1 (-7.0), sec-butyl 415.7 (-5.8), n-propyl 415.6 (-1.9), tert-butyl 413.1 (-5.9), isobutyl 412.9 (0.8), 3-butenyl 412.0 (1.7), cyclopropyl 411.5 (8.4), cyclopropylmethyl 410.5 (3.2), 1-methylcyclopropyl 409.2 (8.0), neopentyl 408.9 (4.8), vinyl 407.5 (16.1), 2-propenyl 405.8 (15.8).
- DePuy, Charles H.,Gronert, Scott,Barlow, Stephan E.,Bierbaum, Veronica M.,Damrauer, Robert
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p. 1968 - 1973
(2007/10/02)
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- Isomeric Characterization of Gaseous Ions. Minimizing C4H8.+ Rearrangment by Dissociating the Corresponding Neutrals
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With use of neutralization-reionization (NR) mass spectrometry, five gaseous C4H8.+ isomers can be structurally characterized by neutralization with sodium to produce excited C4H8 molecules whose dissociation products are reionized to both negative and positive ions.Such NR mass spectra are less characteristic when produced by Cs neutralization, which forms more highly exicted C4H8, or by Hg neutralization followed by dissocation of C4H8 using multiple collisions; on average each collision adds ca. 1.7 eV to the molecule, so that isomerization may occur between collisions.The Na NR spectra show that C4H8.+ ions from all butyl acetate isomers have the expected structure except that 2-C4H8.+ is formed from n-butyl acetate. 2-C4H8.+ and methylcyclopropane.+ appear to be the major products from methylcyclopentane.+. 1-Butanol.+ and cyclohexane.+ predominatly form cyclobutane.+, while β- and γ-valerolactone.+ give 1-C4H8.+ and methylocyclopropane.+, respectively, as major products.
- Feng, Rong,Wesdemiotis, Chrysostomos,Zhang, Mei-Yi,Marchetti, Mauro,McLafferty, Fred W.
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p. 1986 - 1991
(2007/10/02)
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- Synthesis and Thermal Decomposition of Palladacyclopentane Derivatives of the Type (R=H or Me). X-Ray Crystal Structure of
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A series of new palladacyclopentane derivatives of formula has been prepared.The first X-ray crystal structure determination of a palladacyclopentane derivative is reported: the compound gives crystals belonging to the C2/c space group: a=16.643(9), b=11.174(4), c=7.451(3) Angstroem, β=116.05(9) deg, and Z=4; R=0.0340 for 826 observed reflexions.The metal co-ordination is square planar and the molecules lie on a two-fold axis.The palladacyclopentane ring shows a half-chair conformation with the two-fold axis running through Pd and the middle of the C(β)-C(β') bond.A study of the thermal decomposition of the palladacyclopentanes has been carried out: (L=PPh3; L2=dppe, tmen, bipy, dcpe, or dppb) gives butenes as the major products; cyclobutane (L=PPh3) and ethylene (L2=dppe or dcpe) are also formed as minor products.By comparing these results with those for the decomposition of some methyl-substituted palladacyclopentanes, it is shown that the presence of ethylene is not attributable to fragmentation of the metallacyclic skeleton, but rather to the rupture of the P-C bonds of the diphosphine ligands.The decomposition of palladacyclopentanes is also induced by Bun2O*BF3: linear C4 hydrocarbons are formed.
- Diversi, Pietro,Ingrosso, Giovanni,Lucherini, Antonio,Lumini, Tito,Marchetti, Fabio,et al.
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p. 133 - 140
(2007/10/02)
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- Cyclopropane formation from the reaction of (γ-haloalkyl)iron compounds with silver(1+)
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Reaction of C5H5(CO)2Fe(CH2)3Br with AgBF4 in benzene leads to formation of cyclopropane in 73% yield.
- Casey, Charles P.,Smith, Laura J.
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p. 2419 - 2421
(2008/10/08)
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- Hydrogenolysis of Small Cycloalkanes, X. - Catalytic Hydrogenation of Bicycloalkanes
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Dependent on n different products are obtained from bicycloalkanes by hydrogenation on Pt and Pd/C catalysts: from n = 5 onward only methylcycloalkanes of the same ring size; with n = 4 additionally 2-7 percent of cycloheptane is formed; with n = 3 ring enlargement increases to 5-20 percent and with n = 2 cyclopentane is the only product.Mainly butane is formed from bicyclobutane and no intermediate could be detected.Explanations are attempted.The expected products are produced on hydrogenation of methyl-substituted derivatives and spiroalkanes.
- Stahl, Karl-Johannes,Hertzsch, Winfried,Musso, Hans
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p. 1474 - 1484
(2007/10/02)
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- STEREOSPECIFIC PHOTODIMERIZATION OF UNSATURATED COMPOUNDS INDUCED BY NICKEL COMPLEXES
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Irradiation of (ethylene)bis(triphenylphosphine)nickel (1) or bis(triphenylphosphine)nickelacyclopentane induced stereospecific cyclodimerization of substituted olefins such as acrylonitrile and methylacrylate affording trans-1,2-disubstituted cyclobutanes, while 1,7-octadiene was converted to trans-bicyclooctane.Ethylene was photochemically dimerized to cyclo- and linear dimers induced by 1.
- Miyashita, Akira,Ikezu, Shohgo,Nohira, Hiroyuki
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p. 1235 - 1238
(2007/10/02)
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- SINDO1 STUDY OF PHOTOISOMERIZATION AND PHOTOFRAGMENTATION OF CYCLOPENTANONE.
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The photoisomerization of cyclopentanone to 4-pentenal and the photofragmentation to cyclobutane and carbon monoxide or to two ethylene and carbon monoxide was investigated by the SINDO1 method including configuration interaction (CI). Structures and energies of all pertinent ground and excited states as well as transition states and intermediates were calculated. The mechanism for all reactions involves excitation to S//1 and intersystem crossing to T//1 or T//2. The triplets lead to diradical intermediates from which further reaction to the products takes place. The dependence of product distribution on excitation wavelength is discussed.
- Mueller-Remmers,Mishra,Jug
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p. 2538 - 2543
(2007/10/02)
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- OXIDATIVE ADDITION - REDUCTIVE ELIMINATION SEQUENCES IN THE PHOTOCHEMISTRY OF SOME BIS(PHOSPHINE)PLATINUM COMPLEXES
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The photolysis of (L = PPh3, P(p-C6H4CH3)3 complexes in halocarbon solvents (CH2Cl2, CH2Br2) gives C2H4 and the coordinatively unsaturated species .Photolysis of platinum metallacycles (L = PPh3, P(n-Bu)3) generates alkanes
- Bartocci, Carlo,Maldotti, Andrea,Sostero, Silvana,Traverso, Orazio
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p. 253 - 258
(2007/10/02)
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- Sequential Ene Reactions. A New Annelation Procedure
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Alkylidenecycloalkanes react with α,β-unsaturated carbonyl compounds in the presence of Me2AlCl to give bicyclic alcohols resulting from two sequential ene reactions.
- Snider, Barry B.,Deutsch, Ethan A.
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p. 745 - 747
(2007/10/02)
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- Thermochemical Bond Dissociation Energies of Carbon-Magnesium Bonds
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The heats of formation of 29 alkylmagnesium bromides, isobutyl bromide, and neopentyl bromide have been determined, and bond dissociation energies have been derived for the Grignard reagents.For saturated alkyl derivatives the C-Mg bond strength decreases with an increasing number of β-hydrogens in the series methyl, neopentyl, isobutyl, butyl, ethyl, 1-ethylpropyl, 1-methylpropyl, isopropyl, and t-butyl.Bonding in alkyl bromides and alkylmagnesium bromides is discussed.
- Holm, Torkil
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p. 464 - 467
(2007/10/02)
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- The 147-nm Photolyses of Tetramethylene Sulfide, Tetramethylene Sulfoxide, and Tetramethylene Sulfone
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Tetramethylene sulfide, sulfoxide, and sulfone have been photolyzed with 147-nm radiation in the gas and condensed phases.Mechanisms which assume diradical intermediates are presented for the photodecomposition of each compound.The major reaction in all three cases is the elimination of ethylene by a β-cleavage of the initially formed diradical: *XCH2CH2CH2CH2*->*XCH2CH2*+C2H4.The competing β-cleavage produces X=CH2 and C3H6.This second β-cleavage is less important in the sulfoxide and the sulfone than it is in the sulfide.The direct elimination of the sulfur atom, and any attached oxygen atoms, is of no importance in the sulfide and of increasing importance as the oxidation state of the sulfur atom increases.The similarity between the mass spectral fragmentation and the vacuum ultraviolet photochemistry of these compounds is noted and the possible involvement of triplet states is mentioned.
- Scala, A. A.,Colon, Ismael,Rourke, W.
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p. 3603 - 3607
(2007/10/02)
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- Synthesis and Thermal Decomposition of cis-3,4,5,6-Tetrahydropyridazine-3,4-d2. Relative Rates of Rotation, Cleavage, and Closure for Tetramethylene
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The stereospecific syntheses of cis-3,4,5,6-tetrahydropyridazine-3,4-d2 (6) and cis- and trans-cyclobutane-1,2-d2 are reported.The thermal decomposition of cis-3,4,5,6-tetrahydopyridazine (6) (gas phase, 439 deg C) affords 67.1 +/- 0.9percent cis-ethylene-1,2-d2, 16.1 +/- 0.8percent trans-ethylene-1,2-d2, 9.4 +/- 0.4percent cis-cyclobutane-1,2-d2, and 7.4 +/- 0.4percent trans-cyclobutane-1,2-d2.The relative rates of rotation, cleavage, and closure for this 1,2-diazene generated tetramethylene-d2 are k(cleavage)/k(closure) = 2.2 +/- 0.2 and k(rotation)/k(closure) = 12 +/- 3.An extra stereospecific cleavage component (46percent) superimposed on the 1,4-biradical pathway (54percent) from the parent tetrahydropyridazine was found, similar to that observed in the 3,4-dimethyl-3,4,5,6-tetrahydropyridazine thermal reactions.Finally, the experimental data fot the parent 1,4 biradical, tetramethylene, are compared to calculated values in the literature.
- Dervan, Peter B.,Santilli, Donald S.
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p. 3863 - 3870
(2007/10/02)
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- Gas-Phase Photolysis of Sulfoxides. Tetramethylene Sulfoxide
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The reaction channels exhibited during the gas-phase photolysis of tetramethylene sulfoxide (TMSO) have been characterized.Whereas photolysis in the liquid phase produces no hydrocarbon products, photolysis in the gas phase produces ethylene, propylene, cyclopropane, 1-butene, cyclobutane, and small amounts of butadiene.The results are interpreted in terms of a mechanism which involves initial rupture of a C-S bond to form a diradical intermediate.The product composition appears to depend upon the internal energy content of the initially formed diradical.The results are compared to those for cyclopentanone photolysis.
- Dorer, F. H.,Salomon, K. E.
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p. 1302 - 1305
(2007/10/02)
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- Competitive reactions of nucleophiles. Solvolyses of cyclopropylcarbinyl and cyclobutyl methanesulfonates in the presence of NaBH4
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Cyclopropylcarbinyl (I) and cyclobutyl (II) mesylates were solvolysed in aqueous diglyme with or without added NaBH4 under a variety of conditions. The reaction products were isolated and analyzed by VPC. A mixture containing cyclopropylcarbinyl, cyclobutyl and minor quantities of homoallyl products, was obtained in all cases. The proportion of the unsaturated compound was greater in hydrocarbon than in carbinol products, the composition of the mixture depending upon reaction conditions and the starting mesylate. Thus, solvolysis of both I and II yielded cyclopropylcarbinol and cyclobutanol in a ratio of nearly 1:1, while in the hydrocarbon products methylcyclopropane predominated over cyclobutane by a factor of 3 in the reactions of I and by a factor of 2 in the reactions of II. It was shown that a direct displacement reaction of the BH4 ion on the primary mesylate I is not competitive with the solvolysis and cannot therefore be responsible for the above results. It was found that a better yield in hydrocarbons was obtained with I and II than with (1-methylcyclopropyl)carbinyl (III) and 1-methylcyclobutyl (IV) mesylates. The unexpected fact that the BH4- ion competes more efficiently with water for intermediates formed in solvolyses of I and II than for those of III and IV was confirmed by determination of competition factors of N3- ion vs water. In all cases, intermediates formed from I and II showed more discrimination in their reactions with reagents differing in nucleophylicity than did those formed from III and IV. The results indicate that the attack of the nucleophile occurs mostly on the ion pair formed in the rate determining step. The latter reaction is apparently subject to reactivity relationships typical for a direct displacement reaction and not characteristic for free carbonium ions. These facts should be borne in mind when conclusions concerning the structure of carbonium ions are drawn from the composition and structure of solvolysis products. It is concluded that the ion pairs trapped by NaBH4 have different structures, depending upon the starting isomeric mesylate. It is shown that the formation of an equilibrating mixture of classical ions or ion pairs as intermediates in these reactions cannot account for experimental results.
- Majerski,Borcic,Sunko
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p. 301 - 313
(2007/10/05)
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