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141.
Treatment of octa-alkylporphyrins (e.g. 1–3) with mercury(II) acetate in methylene chloride and tetrahydrofuran affords novel complexes (4) containing two porphyrin rings layered between three Hg atoms. A new type of stereoisomerism in regularly substituted porphyrins (e.g. 1a, 2a) is identified; it is observed by NMR spectroscopy and occurs because two forms of the complex (4) are possible, depending upon which faces of the porphyrin molecule are turned in towards the central Hg atom. The NMR spectra also indicate that in concentrated solution the double sandwich complexes (4) are stable towards disproportionation and recombination. On the basis of the inherent geometrical arrangements in the complex (4), an efficient NMR method for unambiguous identification of the four primary type isomers of the aetio- and copro-porphyrin series is described.
In very dilute solution, or in mixtures containing nucleophilic solvents such as pyridine, methanol, dioxan, or tetrahydrofuran (in the absence of excess mercury(II) acetate), the double sandwich complexes (4) are destroyed to afford normal 1:1 metalloporphyrins. 相似文献
142.
143.
Y. P. Khanna E. M. Pearce J. S. Smith D. T. Burkitt H. Njuguna D. M. Hindenlang B. D. Forman 《Journal of polymer science. Part A, Polymer chemistry》1981,19(11):2817-2834
Thermal degradation behavior of poly(1,3-phenylene isophthalamide) and poly(chloro-2,4-phenylene isophthalamide) was investigated with the aid of some appropriate model compounds. The pyrolysis products of these materials were identified by gas chromatography (GC), gas chromatography/Fourier transform infrared spectroscopy (GC/FT-IR), and gas chromatography/mass spectrometry (GC/MS). The residual chars were characterized by IR spectroscopy. Thermogravimetric analysis (TGA) was applied to study the effect of end-group concentration on the degradation characteristics of the two polyamides. Kinetic parameters that describe the thermal degradation of the polyamides were also evaluated by TGA. The results of this investigation suggest that the thermal decomposition of these aromatic polyamides involves homolytic as well as hydrolytic cleavages of the amide units. 相似文献
144.
The antioxidant activities of a number of N-phenyl nitrones containing phenolic functions were compared with N-methyl nitrones and conventional antioxidants in peroxide and TMTD sulphur-less vulcanizates. The N-phenyl nitrones were found to be effectively bound during vulcanization whereas the N-methyl nitrones were not. Unhindered phenols reacted to a higher degree and were relatively more effective than the typical hindered phenol antioxidant structures. A conventional bisphenol was effective in the sulphurless vulcanizate after solvent extraction but this is considered to be due to the formation of an insoluble zinc salt. Synergism was observed in the TMTD sulphurless vulcanizate both before and after extraction. 相似文献
145.
PHOTOINHIBITION OF PHOTOSYNTHESIS IN NATURAL WATERS* 总被引:1,自引:0,他引:1
Raymond C. Smith Karen S. Baker Osmund Holm-Hansen Robert Olson 《Photochemistry and photobiology》1980,31(6):585-592
Abstract— A quantitative analysis of the wavelength-dependent influence of solar irradiance on natural phytoplankton photosynthesis has been made. The effect on productivity due to several different UV radiation regimes has been measured. In the course of this analysis, it has been shown that the biological weighting function for photoinhibition of chloroplasts (Jones and Kok, 1966) allows the calculation of a biologically effective dose which is consistent with the measured photoinhibition in natural phytoplankton populations. The ecological implications of a change in available UV radiation, possibly due to anthropogenic altering of the ozone layer, are explored and it is found that the present static bottle l4 C technique of measuring in situ phytoplankton productivity does not lend itself to assessing accurately the potential ecological consequences of possible increased MUV (middle ultraviolet radiation in the 280–340 nm region) on phytoplankton populations. A small change in MUV has a relatively minor effect on photoinhibition dose rates whereas it has a large potential effect on DNA dose rates. 相似文献
146.
R. W. Smith 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1991,21(1):57-64
Molecular dynamics has been used with a Lennard-Jones (6–12) potential in order to study the decay behavior of neutral Argon clusters containing between 12 and 14 atoms. The clusters were heated to temperatures well above their melting points and then tracked in time via molecular dynamics until evaporation of one or more atoms was observed. In each simulation, the mode of evaporation, energy released during evaporation, and cluster lifetime were recorded. Results from roughly 2000 simulation histories were combined in order to compute statistically significant values of cluster half-lives and decay energies. It was found that cluster half-life decreases with increasing energy and that for a given value of excess energy (defined asE=(E tot ?E gnd)/n), the 13 atom cluster is more stable against decay than clusters containing either 12 or 14 atoms. The dominant decay mechanism for all clusters was determined to be single atom emission. 相似文献
147.
Relative rates of proton and deuteron transfer from CH4D+ and CD4H+ to a number of molecules were examined in a tandem-ion cyclotron resonance instrument. The results were in conflict with the recent work of Sefcik et al. and support a randomized model. 相似文献
148.
Spectra of fluorobenzene (FB), pentafluorobenzene (PFB) and hexafluorobenzene (HFB) from 50000 to 93000 cm−1 are presented. Rydberg series converging to the first and to a higher ionization limit are found in each molecule. The orbital natures of the excited states and ions are discussed. 相似文献
149.
The reaction of Mn(2)(CO)(7)(mu-S(2)), 1, with Pt(PPh(3))(2)(PhC(2)Ph) yielded the new complex, Mn(2)(CO)(6)Pt(PPh(3))(2)(mu(3)-S)(2), 3, by loss of CO and insertion of a Pt(PPh(3))(2) group into the S-S bond of 1. Complex 3 was characterized crystallographically and was found to consist of an open Mn(2)Pt cluster with one Mn-Mn bond, 2.8154(14) A, one Mn-Pt bond, 2.9109(10) A, and two triply bridging sulfido ligands. Compound 3 reacts with CO to form adduct Mn(2)(CO)(6)(mu-CO)Pt(PPh(3))(2)(mu(3)-S)(2), 4. Compound 4 also contains an open Mn(2)Pt cluster with two triply bridging sulfido ligands but has only one metal-metal bond, Mn-Mn = 2.638(2) A. Under nitrogen, compound 4 readily loses CO and reverts back to 3. 相似文献
150.
Amidrazones. VII. Formation of s-triazines by thermolysis of N1-benzyl-substituted amidrazone ylides
Richard F. Smith Richard R. Soelch Timothy P. Feltz Michael J. Martinelli Susan M. Geer 《Journal of heterocyclic chemistry》1981,18(2):319-325
The preparation of ylides of the general structure is described. Thermolysis of 14a (R = CH3, R' = H, Ar = C6H5) gave dimethylamine and 2,4-dimethyl-6-phenyl-s-triazine. Thermolysis of ylides 14b (R = C6H5; R' = CH3, Ar = C6H5) and 14c (R = C6H5, R' = CH3, Ar = p-tolyl) gave dimethylamine, ArCH = NCH3 and 1-methyl-2-Ar-4,6-diphenyl-1,2-dihydro-s-triazines ( 19a,b ). Triazines 19a and 19b were also prepared by condensation of N-methylbenzamidine with benzaldehyde and p-tolualdehyde, respectively. Thermolysis of 14d (R = C6H5, R1 = CH2C6H5,Ar = C6H5) gave 1-benzyl-2,4,6-triphenyl-1,2-dihydro-s-triazine ( 19c ) and N-benzylidenebenzylamine. Mechanistic aspects of these reactions are discussed. 相似文献