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911.
912.
Michael C. Böhm 《Theoretical chemistry accounts》1983,62(4):351-372
The crystal orbital formalism in the tight-binding approximation is combined with a recently developed CNDO/INDO model for transition metal species of the 3d series in order to allow band structure calculations on the Hartree-Fock (HF) SCF level for one-dimensional (1D) chains with organometallic unit cells. The band structure approach based on the CNDO and INDO approximation can be used for any atom combination up to bromine under the inclusion of the 3d series. The matrix elements for the tight-binding Hamiltonian are derived for an improved CNDO and INDO framework. The total energy of the 1D chain is partitioned into one-center contributions and into two-center increments of the intracell and intercell type. Semiempirical band structure calculations on simple model systems are compared with available ab initio data of high quality. 相似文献
913.
The synthesis of an 8-aza-PGE1 analog, (E)-7-[[2-[4-(m-trifluoromethylphenoxy)-3α and 3β-hydroxy-1-butenyl]-5-oxo-pyrrolidinyl]]heptanoic acids is reported. 相似文献
914.
Toy and Stringham recently reported [1] the synthesis of N2F+5 (CF3)3CO-, a salt containing the novel pentafluorohydrazinium cation. This cation would be of significant academic and practical interest [2] since it would constitute the first known example of a substituted NF+4 cation, i.e. an NF+4 cation in which a fluorine ligand is replaced by an NF2 group. According to the authors of [1], N2F+5(CF3)3CO- was formed in a very unusual reaction involving the transfer of a fluorine cation from (CF3)3COF to N2F4 according to: 相似文献
915.
The biradicals generated in the Norrish type II reaction from the triplet manifold have been observed using laser flash photolysis techniques. The spectra and extinction coefficients closely resemble those of typical ketyl radicals. Typical lifetimes are in the 40–100 ns range depending on the solvent. Their interaction with oxygen is essentially diffusion controlled. 相似文献
916.
W. H. Daly Chien-Da S. Lee C. G. Overberger 《Journal of polymer science. Part A, Polymer chemistry》1971,9(6):1723-1739
Poly-S-vinyl-O-tert-butylthiocarbonate is an excellent precursor to poly(vinyl mercaptan) because the tert-butyloxycarbonyl blocking group can be removed by either acid hydrolysis or thermolysis under conditions which minimize the oxidation of the liberated mercaptan to disulfide. Dilatometric studies of the homopolymerization of S-vinyl-O-tert-butylthiocarbonate demonstrated that the polymerization rate was directly proportional to the concentration of free-radical initiator; no thermal initiation was observed. The molecular weight of the homopolymers and copolymers ranged from 30,000 to 50,000 (GPC). Copolymerization of S-vinyl-O-tert-butylthiocarbonate (M2) with styrene, (r1 = 3.0, r2 = 0.2), methyl methacrylate (r1 = 1.40, r2 = 0.17) and vinyl acetate (r1 = 0.04, r2 = 11.0) indicated that a sulfur atom adjacent to the vinyl group increases the resonance stability (Q2 = 0.5) and the electron density (e2 = ?1.4) of the double bond and the corresponding radical. Water-soluble copolymers could be prépared by incorporating either N-vinylpyrrolidone (r1 = 0.12, r2 = 3.94) or N-isopropylacrylamide (r1 = 1.17, r2 = 0.3) with M2. The water solubility of the copolymers decreased markedly when the tert-butyloxycarbonyl group was removed. Copolymers of M2 with N-vinyl-O-tert-butylcarbamate (r1 = 0.13, r2 = 5.10) were utilized to prepare crosslinked poly(vinyl amine–vinyl mercaptan); the crosslinking resulted from urea linkages formed during thermolysis of the copolymer. 相似文献
917.
K. Strijckmans N. De Brucker C. Vandecasteele 《Journal of Radioanalytical and Nuclear Chemistry》1985,96(4):389-397
A method for the determination of sulphur in fly ash by instrumental proton activation analysis using the34S/p,n/34mCl reaction was developed. The 2128.5 keV and 3305.0 keV -rays of34mCl /t=32.0 min/ were measured on a Ge/Li/ -spectrometer, shielded with a lead absorber to attenuate low energy -rays. Irradiation and measuring conditions were optimized. The detection limit for instrumental analysis is 0.3 to 1 mg g–1 and the standard deviation is cca. 4% for a typical sample. 相似文献
918.
l-(o-Carboxyphenyl)-3-hydroxy-3-methyltriazene is proposed as an excellent reagent for the spectrophotometric determination of iron(III) and titanium(IV), and also for the separation of titanium from a large quantity of iron as well as other cations and anions. Iron(III) forms an anionic violet 1:2 complex at pH 4.0–9.4, and a cationic green 1:1 complex at pH 1.5–2.0, with absorption maxima at 570 nm and 660 nm, respectively. The violet complex is quantitatively extracted in chloroform containing n-octylamine at pH 3.0–9.0. The green and the violet iron(III) complexes obey Beer's law, the respective optimal ranges being 8.9–35.8 and 3.9–11.2 p.p.m. The yellow titanium chelate extracted into chloroform (absorption maximum at 410 nm) between pH 1.0 and 3.5, can be re-extracted into concentrated sulphuric acid a violet colour being produced with absorption maximum at 530 nm. Beer's law is obeyed in the ranges 0.8–5.7 p.p.m. for the titanium complex in chloroform and 3.4–19.2 p.p.m. when extracted in concentrated sulphuric acid. Interferences from diverse ions are not severe. Procedures for the separation and determination of titanium in the presence of a large quantity of iron are given. The isolation of the iron(III) and vanadium(IV and V) complexes, and their properties, are described. 相似文献
919.
G.C. PappalardoS. Pistarà 《Tetrahedron》1972,28(6):1611-1617
The electric dipole moments of three diphenyl thioethers have been measured in benzene solution at 25· and the conformational analysis of bis(o-nitrophenyl) sulphide has been carried out by vector addition. The results show that this compound exists in a twisted conformation with the phenyl rings considerably rotated from coplanarity with respect to the C-S-C plane and indicate that in o,o′-disubstituted derivatives of diphenyl sulphide steric rather than conjugative effects operate in determining the conformational preference. 相似文献
920.
The structures and configurations of two new β-carbolinic alkaloids, strychnohirsutine 1 and tetra-dehydrostrychnohirsutine 2, isolated from stem and root bark of Strychnos hirsuta, were reported. 1H NMR data of N,O-diacetylstrychnohirsutine 5 and 1H and 13C NMR data of O-acetyltetradehydrostrychnohirsutine 4 were listed. Alkaloid 1 was converted into 2 by catalytic dehydrogenation. 相似文献