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Gair D. Brown Joseph P. Ingold Scote Spence Jack G. Paxton Jr. 《Fiber and Integrated Optics》1990,9(4):381-392
MIL-S-901 High Impact Shock tests were performed on commercial-grade and ruggedized fiber-optic connectors, splices, and switches. Both single-mode and multimode connectors and splices were tested. Only multimode switches were tested. Transient losses of varying magnitudes and durations were observed. Most components suffered no permanent degradation. 相似文献
13.
This tutorial review is designed to dispel the myth, still believed by many synthetic organic chemists, that radical-based syntheses are free from significant solvent effects. However, many synthetically valuable radical reactions do exhibit large kinetic solvent effects. It is therefore important to select the solvent for any proposed radical synthesis with considerable care if good product yields are to be achieved. 相似文献
14.
Billone PS Johnson PA Lin S Scaiano JC DiLabio GA Ingold KU 《The Journal of organic chemistry》2011,76(2):631-636
Differences in O-H bond dissociation enthalpies (ΔBDEs) between the hydroxylamine of (15)N-labeled TEMPONE and 10 N,N-di-tert-alkyl hydroxylamines were determined by EPR. These ΔBDEs, together with the g and a(N) values of the derived nitroxide radicals, are discussed in relation to various geometric, intramolecular dipole/dipole, and steric effects and in relation to the results from DFT calculations. We find that dipole/dipole interactions are the dominant factors in dictating a(N) values and O-H BDEs in all of these structurally similar nitroxides and hydroxylamines, respectively. The importance of including the Boltzmann distribution of conformations for each nitroxide in the a(N) calculations is emphasized. 相似文献
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B. Lott J. L. Charvet E. Crema G. Duchêne H. Doubre J. Fréhaut J. Galin B. Gatty D. Guerreau G. Ingold D. Jacquet U. Jahnke D. X. Jiang C. Magnago M. Morjean Y. Patin E. Piasecki J. Pouthas Y. Pranal F. Saint-Laurent E. Schwinn A. Sokolov J. L. Uzureau X. M. Wang 《Zeitschrift für Physik A Hadrons and Nuclei》1993,346(3):201-208
Inclusive neutron multiplicity distributions were measured by means of 4π liquid-scintillator detectors for Ar and Kr-induced reactions at 44 MeV/nucleon and 32 MeV/nucleon, respectively. For all the systems studied, the observed distributions exhibit a bump structure at large multiplicity, corresponding to highly dissipative collisions. For Ar-induced reactions, the excitation energies necessary to explain the most probable neutron multiplicity associated with these dissipative collisions are estimated, the correspondence between excitation energy and neutron multiplicity being calculated in the framework of the statistical model. The so-obtained values of excitation energies, which are systematically lower than those predicted using the massive-transfer picture, are discussed. 相似文献
18.
A competitive method involving the direct measurement of radical concentrations by EPR spectroscopy has been used to show that in solution at 25°C the rate constants for the bimolecular self-reactions of ethyl, isopropyl, tert-butyl, cyclopentyl, and trichloromethyl are all approximately equal, as had been indicated previously by direct measurement of the rate constants for decay of these radicals. 相似文献
19.
The kinetics of the photoinitiated reductions of methyl iodide and carbon tetrachloride by tri-n-butylgermanium hydride in cyclohexane at 25°C have been studied and absolute rate constants have been measured. Rate constants for the combination of CH3? and CCl3? radicals are equal within experimental error and are also equal to the values found for the self-reactions of most non-polymeric radicals in low viscosity solvents, i.e. ~1–3 × 109 M?1 sec?1. Rate constants for hydrogen atom abstraction by CH3? and CCl3? radicals are both ~1?2 × 105 M?1 sec?1. Tri-n-butyltin hydride is about 10–20 times as good a hydrogen donor to alkyl radicals as is tri-n-butylgermanium hydride. The strength of the germanium–hydrogen bond, D(n-Bu3Ge–H) is estimated to be approximately 84 kcal/mole. 相似文献
20.
In solution, the self-exchange reactions for oxygen-centered pi-radicals, e.g., PhO. + PhOH <==>PhOH + PhO., are known to occur with low activation enthalpies (E(a) approximately equal to 2 kcal/mol). For the PhO./PhOH couple and, we conclude, for other O-centered pi-radicals, exchange occurs by proton-coupled electron transfer (PCET) with the proton transferred between oxygen electron pairs while the electron migrates between oxygen orbitals orthogonal to the -O- - -H- - -O- transition state plane (Mayer et al. J. Am. Chem. Soc. 2002, 123, 11142). Iminoxyls, R(2)C=NO., are sigma-radicals with substantial spin density on the nitrogen. The R(2)C=NO./R(2)C=NOH self-exchange has a significant E(a) (Mendenhall et al. J. Am. Chem. Soc. 1973, 95, 627). For this exchange, DFT calculations have revealed a counterintuitive cisoid transition state in which the seven atoms, >C=NO- - -H- - -ON=C<, lie in a plane (R = H, Me) or, for steric reasons, two planes twisted at 45.2 degrees (R = Me(3)C). The planar transition state has the two N-O dipoles close to each other and pointing in the same direction and an O- - -H- - -O angle of 165.4 degrees . A transoid transition state for R = H lies 3.4 kcal/mol higher in energy than the cisoid despite a more favorable arrangement of the dipoles and a near linear O- - -H- - -O. It is concluded that iminoxyl/oxime self-exchange reactions occur by a five-center, cyclic PCET mechanism with the proton being transferred between electron pairs on the oxygens and the electron migrating between in-plane orbitals on the two nitrogens (R(N-N) = 2.65 A). The calculated E(a) values (8.8-9.9 kcal/mol) are in satisfactory agreement with the limited experimental data. 相似文献