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91.
Intramolecular 6-exolendo-trig and 5-exo-trig cyclisations of aryl radical intermediates to the alpha-, beta- and gamma-carbons of pyridine have been shown to be facile processes at neutral pH. The tether conjoining the radical donor to the pyridine plays an important role in determining the outcome of the reaction. When a Z-alkene is used as a tether, ortho-cyclisation proceeds in good yield. A more complex course is followed when a saturated two carbon tether is employed, leading to products derived from hydrogen atom abstraction, ipso-cyclisation and ortho-cyclisation pathways. All attempts to effect 5-exolendo-trig cyclisations failed. Tributyltin hydride, tris(trimethylsilyl)silane, tris(trimethylsilyl)germane and, in part, samarium(II) iodide can each be employed as mediators of the reaction. 相似文献
92.
A. Patterson G. J. Sutton B. J. Tighe 《Journal of polymer science. Part A, Polymer chemistry》1973,11(9):2343-2355
The thermal degradation of two β-chlorinated versions of poly(isopropylidene carboxylate) has been studied by the combined thermogravimetric and gas evolution techniques described previously. Poly(3-chloro-2-methyl-2-hydroxypropionic acid) was found to decompose by a predominantly first-order process which was characterized by kinetic parameters similar to those obtained for poly(isopropylidene carboxylate). These are interpreted in terms of an intramolecular ester-exchange process. As the reaction proceeds intermolecular elimination of hydrogen chloride leads to crosslinking and ultimately to the formation of a carbonaceous char. This process is much more marked in the randomly β-chlorinated analog of poly(isopropylidene carboxylate). With this polymer, drastic deviation from first-order behavior is observed in thermogravimetric results, even in the early stages of reaction. Gas evolution analysis, being more influenced by degradation fragments having an appreciable vapor pressure, yields reasonable first-order data and indicates that the intramolecular interchange mechanism is still an important process. In general, the introduction of β-chlorine atoms is seen to reduce the rate of thermal decomposition of poly-α-esters. 相似文献
93.
Chen Z Sutton LR Moran D Hirsch A Thiel W Schleyer Pv 《The Journal of organic chemistry》2003,68(23):8808-8814
Density functional theory energies, geometries, and population analyses as well as nucleus-independent chemical shifts (NICS) have been used to investigate the structural and magnetic evidence for cyclic CnSn(2-) and CnSn (n = 3-6) electron delocalization. Localized molecular orbital contributions to NICS, computed by the individual gauge for localized orbitals method, dissect pi effects from the sigma single bonds and lone pair influences. CnSn(2-) (n = 3-5) structures in Dnh symmetry are minima. Their aromaticity decreases with increasing ring size. C3S3(2-) is both sigma and pi aromatic, while C4S4(2-) and C5S5(2-) are much less aromatic. NICS(0)pi, the C-C(pi) contribution to NICS(0) (i.e., at the ring center), decreases gradually with ring size. In contrast, cyclic C6S6(2-) prefers D2h symmetry due to the balance between aromaticity, strain energy, and the S-S bond energies and is as aromatic as benzene. The theoretical prediction that C6S6(6-) has D6h minima was confirmed by X-ray structure analysis. Comparisons between thiocarbons and oxocarbons based on dissected NICS analysis show that CnSn(2-) (n = 3-5) and C6S6(6-) are less aromatic in Dnh symmetry than their oxocarbon analogues. 相似文献
94.
A review of X-ray intensity fluctuation spectroscopy 总被引:1,自引:0,他引:1
This article reviews the literature on X-ray fluctuation intensity spectroscopy or, as it is often called, X-ray photon correlation spectroscopy. It highlights measurements using different types of diffuse scattering. To cite this article: M. Sutton, C. R. Physique 9 (2008). 相似文献
95.
Albert Murad Sutton 《International Journal of Theoretical Physics》2007,46(5):1065-1082
There exist classical systems whose canonical quantization yields relativistic wave equations. As a constructive proof, the
classical mechanics of a translating-rotating five-frame is considered. Its quantization yields the Dirac, Weyl, Klein-Gordon,
Maxwell-Proca, and higher spin equations, together with a rotational mass spectrum for the states predicted. 相似文献
96.
Rudd RE Briggs GA Sutton AP Medeiros-Ribeiro G Williams RS 《Physical review letters》2003,90(14):146101
We present a nanostructure diagram for use in designing heteroepitaxial systems of quantum dots. The nanostructure diagram is computed using a new equilibrium statistical physics model and predicts the island size and shape distributions for a range of combinations of growth temperature and amount of deposited material. The model is applied to Ge on Si(001), the archetype for bimodal island growth, and the results compare well with data from atomic force microscopy of Ge/Si islands grown by chemical vapor deposition. 相似文献
97.
High-power dual-rod Yb:YAG laser 总被引:17,自引:0,他引:17
Honea EC Beach RJ Mitchell SC Skidmore JA Emanuel MA Sutton SB Payne SA Avizonis PV Monroe RS Harris DG 《Optics letters》2000,25(11):805-807
We describe a diode-pumped Yb:YAG laser that produces 1080 W of power cw with 27.5% optical optical efficiency and 532 W Q-switched with M(2)=2.2 and 17% optical-optical efficiency. The laser uses two composite Yb:YAG rods separated by a 90 degrees quartz rotator for bifocusing compensation. A microlensed diode array end pumps each rod, using a hollow lens duct for pump delivery. By changing resonator parameters we can adjust the fundamental mode size and the output beam quality. Using a flattened Gaussian intensity profile to calculate the mode-fill efficiency and clipping losses, we compare experimental data with modeled output power versus beam quality. 相似文献
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