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61.
Isborn C Hrovat DA Borden WT Mayer JM Carpenter BK 《Journal of the American Chemical Society》2005,127(16):5794-5795
High-level electronic structure calculations have been used to study the factors contributing to the barriers to degenerate hydrogen-atom transfer (HAT) reactions. Understanding of these reactions is a prerequisite to the development of any more general theory of HAT reactions, and yet, the existing models for such reactions perform quite poorly when applied to even simple self-exchanges. The reasons behind these failures are elucidated in the present work. They include a near cancellation of bond-strength effects between reactant and transition state, as well as a strong dependence of the geometry of the transition state on the nature of the heavy atoms. 相似文献
62.
The development of a novel route for the synthesis of a new class of compounds is described. The first tripodal, tris-indole amines are prepared by straightforward routes. 相似文献
63.
64.
The diffusion coefficient for Fe in Y from Mössbauer experiments is several orders of magnitude lower than from bulk diffusion measurements. This can be explained by a combination substitution-interstitial diffusion mechanism. 相似文献
65.
Crosslinks are introduced by γ irradiation into 1,2-polybutadiene while strained in uniaxial extension near Tg with stretch ratio λ0, thereby trapping a proportion of the entanglements originally present. The stress at any subsequent strain λ is accurately given by the sum σN + σx, where σN is the stress contributed by a trapped entanglement network with λ = 1 as reference and a Mooney–Rivlin stress-strain relation, and σx is that contributed by a crosslink network with λ = λ0 as reference and neo-Hookean stress-strain relation. The birefringence is accurately given as δn = ?NσN + ?xσx, where the ?'s are the respective stress-optical coefficients. From measurements at λ = λ0 where σx = 0, ?N can be determined separately. For polymer with 88% 1,2 microstructure, ?N and ?x are nearly equal and independent of irradiation dose, though strongly dependent on temperature. For polymer with (95–96)% 1,2, ?N and ?x are different (even opposite in sign) and dependent on dose. This behavior is associated with a side reaction of cyclization by the γ irradiation, which is inhibited by the 1,4 moiety in the polymer with lesser 1,2 content. It is responsible for residual birefringence in the state of ease (λ = λs) where σN = –σx and the stress is zero. 相似文献
66.
67.
Reingold JA Uk Son S Bok Kim S Dullaghan CA Oh M Frake PC Carpenter GB Sweigart DA 《Dalton transactions (Cambridge, England : 2003)》2006,(20):2385-2398
Coordination of the carbocyclic ring of hydroquinones to electrophilic transition-metal fragments such as Mn(CO)3+ and Rh(COD)+ produces stable pi-bonded eta6-complexes that are activated to facile reversible deprotonation of the -OH groups. The deprotonations are accompanied by electron transfer to the transition metal, which acts as an internal oxidizing agent or electron sink. With manganese as the metal, the resulting eta5-semiquinone and eta4-quinone complexes have been used to synthesize one- two- and three-dimensional polymeric metal-organometallic coordination networks. With rhodium as the metal, the pi-quinonoid complexes have been demonstrated to play a unique role in multifunctional C-C coupling catalysis and in the synthesis of new organolithium reagents. Both classes of pi-quinonoid complexes appear to have significant applications in nanochemistry by providing an excellent vehicle for templating the directed self-assembly of nanoparticles into functional materials. 相似文献
68.
Rudolph D Carlsson BG Ragnarsson I Aberg S Andreoiu C Bentley MA Carpenter MP Charity RJ Clark RM Cromaz M Ekman J Fahlander C Fallon P Ideguchi E Macchiavelli AO Mineva MN Reviol W Sarantites DG Seweryniak D Williams SJ 《Physical review letters》2006,96(9):092501
High-spin states in 58Ni have been investigated by means of the fusion-evaporation reaction 28Si(32S, 2p)58Ni at 130 MeV beam energy. Discrete-energy levels are observed in 58Ni at record-breaking 42 MeV excitation energy and angular momenta in excess of 30h. The states form regular rotational bands with unprecedented high rotational frequencies. A comparison with configuration dependent cranked Nilsson-Strutinsky calculations reveals an exceptional two-band crossing scenario, the interaction strength of which is strongly shape dependent. 相似文献
69.
Comerford DW Cheesman A Carpenter TP Davies DM Fox NA Sage RS Smith JA Ashfold MN Mankelevich YA 《The journal of physical chemistry. A》2006,110(9):2868-2875
Experimental and modeling studies of the gas-phase chemistry occurring in dilute, hot filament (HF) activated B2H6/H2 and B2H6/CH4/H2 gas mixtures are reported. Spatially resolved relative number densities of B (and H) atoms have been measured by resonance enhanced multiphoton ionization methods, as a function of process conditions (e.g. the HF material and its temperature, the B2H6/H2 mixing ratio, and the presence (or not) of added CH4). Three-dimensional modeling of the H/B chemistry prevailing in such HF activated gas mixtures using a simplified representation of the gas phase chemistry succeeds in reproducing all of the experimentally observed trends, and in illustrating the key role of the "H-shifting" reactions BHx + H <= => BHx-1 + H2 (x = 1-3) in enabling rapid interconversion between the various BHx (x = 0-3) species. CH4 addition, at partial pressures appropriate for growth of boron-doped diamond by chemical vapor deposition methods, leads to approximately 30% reduction in the measured B atom signal near the HF. The modeling suggests that this is mainly due to concomitant H atom depletion near the HF, but it also allows us a first assessment of the possible contributions from B/C coupling reactions upon CH4 addition to HF activated B2H6/H2 gas mixtures. 相似文献
70.
Son SU Reingold JA Carpenter GB Sweigart DA 《Chemical communications (Cambridge, England)》2006,(7):708-710
The ionic complexes [(1,4- and 1,3-hydroquinone)Rh(P(OPh)3)2]BF4 form porous organometallic structures dictated by charge assisted hydrogen bonding. 相似文献