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Hydrogen Shifts (hydrogen + shift)
Selected AbstractsRuthenium-Catalyzed Cycloisomerization of cis-3-En-1-ynes to Cyclopentadiene and Related Derivatives Through a 1,5-Sigmatropic Hydrogen Shift of Ruthenium,Vinylidene Intermediates.CHEMINFORM, Issue 50 2005Swarup Datta Abstract For Abstract see ChemInform Abstract in Full Text. [source] Synthesis and Use of New Substituted 1,3,5-Hexatrienes in Studying Thermally Induced 6, -Electrocyclizations,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 23 2007Hans Wolf Sünnemann Abstract An acyclic, two heterocyclic, and two bicyclic alkenylstannanes, 3, 4a, 4b, 8 and 11, respectively, were synthesized in yields ranging from 43 to 97,%, and each was subjected to a sequence of Stille and Heck couplings with 2-bromocyclohexenyl triflate (13) and alkyl (tert -butyl and methyl) acrylate to furnish seven new 1,3,5-hexatrienes 19, 20, 21, 22 - tBu, 22 -Me, 23 and 43, respectively, in 58,84,% yields. For the alkenylstannanes 4a,b, 8 and 11, customized combinations of catalysts had to be used. The Stille,Heck sequence involving 13, 3 and tert -butyl acrylate could be performed in a one-pot mode and proceeded in 75,% yield. The hexatrienes were heated in decalin solutions so as to effect 6,-electrocyclization. Temperatures and reaction times were optimized individually. The hexatrienes 29, 31 and 36 gave the bi- and tricyclic cyclohexadienes 28, 30 and 34, incorporating allylic alcohol and allyl ether termini, by 6,-electrocyclization and subsequent [1,5]-hydrogen shift, as single products in good yields (85,93,%). In contrast, the hexatrienes 19, 20, 21 and 39 furnished mixtures of the initial electrocyclization products 26, 32, 37 and 40 as well as the products of a subsequent [1,5]-hydrogen shift 27, 33, 38 and 41, respectively. The tricyclic hexatrienes 22 - tBu, 22 -Me and 23 bearing alkyl (tert -butyl, methyl) acrylate termini also selectively gave the tetracyclic dienes 48 - tBu, 48 -Me and 50 in 71,77,% yields by electrocyclizations and subsequent hydrogen shifts.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Reaction of H + ketene to formyl methyl and acetyl radicals and reverse dissociationsINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 1 2003Jongwoo Lee Thermochemical properties for reactants, intermediates, products, and transition states important in the ketene (CH2CO) + H reaction system and unimolecular reactions of the stabilized formyl methyl (C·H2CHO) and the acetyl radicals (CH3C·O) were analyzed with density functional and ab initio calculations. Enthalpies of formation (,Hf°298) were determined using isodesmic reaction analysis at the CBS-QCI/APNO and the CBSQ levels. Entropies (S°298) and heat capacities (Cp°(T)) were determined using geometric parameters and vibrational frequencies obtained at the HF/6-311G(d,p) level of theory. Internal rotor contributions were included in the S and Cp(T) values. A hydrogen atom can add to the CH2 -group of the ketene to form the acetyl radical, CH3C·O (Ea = 2.49 in CBS-QCI/APNO, units: kcal/mol). The acetyl radical can undergo ,-scission back to reactants, CH2CO + H (Ea = 45.97), isomerize via hydrogen shift (Ea = 46.35) to form the slight higher energy, formyl methyl radical, C·H2CHO, or decompose to CH3 + CO (Ea = 17.33). The hydrogen atom also can add to the carbonyl group to form C·H2CHO (Ea = 6.72). This formyl methyl radical can undergo , scission back to reactants, CH2CO + H (Ea = 43.85), or isomerize via hydrogen shift (Ea = 40.00) to form the acetyl radical isomer, CH3C·O, which can decompose to CH3 + CO. Rate constants are estimated as function of pressure and temperature, using quantum Rice,Ramsperger,Kassel analysis for k(E) and the master equation for falloff. Important reaction products are CH3 + CO via decomposition at both high and low temperatures. A transition state for direct abstraction of hydrogen atom on CH2CO by H to form, ketenyl radical plus H2 is identified with a barrier of 12.27, at the CBS-QCI/APNO level. ,Hf°298 values are estimated for the following compounds at the CBS-QCI/APNO level: CH3C·O (,3.27), C·H2CHO (3.08), CH2CO (,11.89), HC·CO (41.98) (kcal/mol). © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 35: 20,44, 2003 [source] Dual Supermesityl Stabilization: A Room-Temperature-Stable 1,2,4-Triphosphole Radical, Sigmatropic Hydrogen Rearrangements, and Tetraphospholide Anion,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 15 2008Alex S. Ionkin Abstract Cesium 3,5-bis(2,4,6-tri- tert -butylphenyl)-1,2,4-triphospholide (12) and cesium 5-(2,4,6-tri- tert -butylphenyl)tetraphospholide (13) were synthesized and isolated with flat five-membered rings, which are an indication of the aromaticity in these anions. Compound 13 is the first example of a stable tetraphospholide anion, which is structurally characterized. Kinetic stabilization of the 1,2,4-triphospholide system by two supermesityl groups resulted in the detection of the room-temperature-stable radical 17 and the observation of a series of successive sigmatropic hydrogen shifts in the first stable 1H -1,2,4-triphosphole 14 with a P,H bond.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] NMR,spectroscopic investigation of o-nitrosobenzoic acidMAGNETIC RESONANCE IN CHEMISTRY, Issue 12 2008Klaus Schaper Abstract The synthesis of o -nitrosobenzoic acid 2 has been known for more than 100 years, and the photochemical preparation from o -nitrobenzaldehyde 1 became a textbook example for [1,5]-hydrogen shifts. However, neither the 1H,NMR spectra nor the 13C{1H},NMR of this compound have been reported so far. This fact can most likely be attributed to the monomer,dimer equilibrium of the nitrosobenzoic acid, which leads to rather complex, concentration-dependent NMR spectra. In this paper, we report a thorough investigation of these spectra. In the 13C-{1H}-NMR spectra, all 21 lines could be assigned to the monomeric form, the E -dimer, and the Z -dimer. Copyright © 2008 John Wiley & Sons, Ltd. [source] Anomalous capacitance,voltage characteristics of Pt,AlGaN/GaN Schottky diodes exposed to hydrogenPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010Yoshihiro Irokawa Abstract We have investigated the interaction of hydrogen with Pt-AlGaN/GaN Schottky barrier diodes (SBDs) using a low-frequency capacitance-voltage (C-V) technique. At a frequency of 1kHz, the C-V curve in hydrogen shifts toward negative bias values as compared with that in nitrogen. As the frequency decreases from 1kHz to 1Hz, the capacitance in hydrogen significantly increases and the fluctuations of the capacitance are observed. These C-V characteristics are quite anomalous and have not been reported yet, suggesting the formation of interfacial polarization which could be attributable to hydrogen-related dipoles. The fluctuation of the capacitance may be related to the alignment of the dipoles. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||