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811.
Cellulose acetate samples with a range of degrees of substitution (DS) were prepared by deacetylation of cellulose acetate (DS = 2.5). Chiral nematic solutions of the samples were prepared in formic acid. A handedness reversal from left to right was observed as the DS used to prepare the mesophase increased from 1.8 to 2.4. By selection of a suitably long-pitch mesophase, chiral nematic films cast from a CA (DS = 2.2)/formic acid solution showed a feint reflection of circularly polarized blue light. Deacetylation of this CA film gave a chiral nematic cellulose film with a more intense reflection band at the same wavelength. The improvement in intensity is attributed to the higher intrinsic birefringence of cellulose compared to cellulose acetate. 相似文献
812.
Maheswaran Hariharasarma Charles H. Lake Charles L. Watkins Gary M. Gray 《Journal of organometallic chemistry》1999,580(2):1541
Chlorodiphenylphosphine and 2,2′-biphenylylenephosphorochloridite react with 2-hydroxy-2′-(1,4-bisoxo-6-hexanol)-1,1′-biphenyl to yield the new α,ω-bis(phosphorus-donor)-polyether ligands, 2-Ph2PO(CH2CH2O)2–C12H8-2′-OPPh2 (1) and 2-(2,2′-O2C12H8)P(CH2CH2O)2–C12H8-2′-P(2,2′-O2C12H8) (2). These ligands react with Mo(CO)4(nbd) to form the monomeric metallacrown ethers, cis-Mo(CO)4{2-Ph2PO(CH2CH2O)2–C12H8-2′-OPPh2} (cis-3) and cis-Mo(CO)4{2-(2,2′-O2C12H8)P(CH2CH2O)2–C12H8-2′-P(2,2′-O2C12H8)} (cis-4), in good yields. The X-ray crystal structures of cis-3 and cis-4 are significantly different, especially in the conformation of the metal center and the adjacent ethylene group. The very different 13C-NMR coordination chemical shifts of this ethylene group in cis-3 and cis-4 suggest that the solution conformations of these metallacrown ethers are also quite different. Both metallacrown ethers undergo cis–trans isomerization in the presence of HgCl2. Although the cis–trans equilibrium constants for the isomerization reactions are nearly identical, the isomerization of cis-3 is more rapid. Phenyl lithium reacts with cis-3 to form the corresponding benzoyl complexes but does not react with either trans-3 or cis-4. Both the slower rate of cis–trans isomerization of cis-4 and its lack of reaction with PhLi are consistent with weaker interactions between the hard metal cations and the carbonyl oxygens in both trans-3 and cis-4. 相似文献
813.
K. C. Nicolaou David Gray Jinsung Tae 《Angewandte Chemie (International ed. in English)》2001,40(19):3675-3678
814.
815.
816.
K. C. Nicolaou David Gray Jinsung Tae 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2001,113(19):3787-3790
817.
Samuel B. Owens Jr. Abha A. Kaisare Gary M. Gray 《Journal of chemical crystallography》2007,37(10):655-661
Abstract X-ray crystal structures of [Et3NH][{(CO)5Mo(P(OCH2CMe2CH2O)O)}2H], 3, and (CO)5Mo{μ-Ph2POPPh2}Mo(CO)5, 2, are reported. Crystallization of 3 occurs in P-1 space group with a = 9.6944(19) ?, b = 10.814(2) ?, c = 19.730(4) ?, α = 94.24(3)°, β = 92.23(3)°, γ = 113.47(3)°,
Z = 4. Crystallization of 2 occurs in C2/c space group with a = 10.357(2) ?, b = 20.149(4) ?, c = 17.155(3) ?, α = 90°, β = 97.28(3)°, γ = 90°, Z = 8.
Compound 2 is a bimetallic complex with a P–O–P bridging group containing bond distances similar to that of other complexes in which
two metal centers are bridged by a single R2POPR2 ligand. Compound 3 contains intermolecular hydrogen bonded P–O–H–O–P linkages with bond distances comparable to those seen in similar structures
with intramolecular hydrogen bonding suggesting that the distance is a function of the nature of the bond and not affected
by the cis arrangement of the ligands about the metal center.
Graphical abstract
X-ray Crystal Structures of [Et
3
NH][{(CO)
5
Mo(P(OCH
2
CMe
2
CH
2
O)
O)}
2
H]
and (CO)
5
Mo{μ-Ph
2
POPPh
2
}Mo(CO)
5
, Two Complexes Derived from the Hydrolysis of Coordinated Chloro-Phosphorous-Donor Ligands
Samuel B. Owens Jr., Abha A. Kaisare and Gary M. Gray
X-ray crystal structures of [Et3NH][{(CO)5Mo(P(OCH2CMe2CH2O)O)}2H], 3, and
(CO)5Mo{μ-Ph2POPPh2}Mo(CO)5, 2, have been determined.
相似文献
818.
The octaethylporphyrin(OEP) complexes of iron(III) chloride, iron(III) acetate, thallium(III) hydroxide, zinc(II), and cobalt(II) and the mesoporphyrin IX dimethyl ester (MPDME) complexes of zinc(II) and iron(III) chloride were reacted with a 20:1 ratio of NO2 to metalloporphyrin in CH2Cl2. The +3 metalloporphyrins gave products which had a nitromethyl group in each of the four meso positions of the porphyrin ring and a chloride ion bound to the metal atom. The products of +2 metalloporphyrin reaction had a nitro group bound in each of the meso positions. The spectral and electrochemical properties of some of the products were measured. 36Cl labelled OEPFeCl was reacted with NO2 in CH2Cl2. The product, meso-tetranitromethyl OEPFeCl, had 17% of the original activity which indicates that the chloride ion bound to the iron is exchanged with chloride ions formed in the reaction. The nitromethylation reaction appears to involve initially the displacement of chloride from iron(III) by NO2 and solvent attack on the bound NO2. The meso-nitration of the +2 metalloporphyrin by NO2 has been proposed to proceed by a π-cation radical mechanism (E.C. Johnson and D. Dolphin, TetrahedronLetters 2197 (1976). 相似文献
819.
Sato K. Miyake T. Morishita A. Matsuta K. Minamisono T. Tanigaki M. Takeda S. Mihara M. Fukuda M. Nojiri Y. Minamisono K. Fukao T. Matsumoto Y. Ohtsubo T. Fukuda S. Momota S. Yoshida K. Ozawa A. Kobayashi T. Tanihata I. Sagawa H. Kitagawa H. Krebs Gray F. Alonso Jose R. Symons T. James M. 《Hyperfine Interactions》1999,120(1-8):661-665
The electric quadrupole interaction of 19O(Iπ=(5/2)+, T1/2=27.0 s) in TiO2 single crystal was studied in detail by means of the β-NQR to determine the electric quadrupole moments Q of short-lived
β-emitting nuclei 19O and 13O(Iπ=(3/2)-, T1/2=8.6 ms). Two implantation sites were found for the implanted O nucleus and the quadrupole coupling constants of 19O at these sites were determined. We observed FT-NMR of the enriched stable isotope 17O in TiO2 and obtained the electric field gradient (EFG) at the oxygen substitutional site. With this knowledge, we have determined
Q(13O)=11.0 ± 1.3 mb and Q(19O)=3.7 ± 0.4 mb. The present results are compared with the theoretical values calculated by the shell model code, OXBASH and
by the Hartree–Fock calculation with the realistic potential.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
820.