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951.
Gates DP Park P Liang M Edwards M Angelakos C Liable-Sands LM Rheingold AL Manners I 《Inorganic chemistry》1996,35(15):4301-4309
The reactions of the cyclic thionylphosphazenes [NSOX(NPCl(2))(2)] (1, X = Cl; 2, X = F) with three oxygen-based nucleophiles of increasing basicity, sodium phenoxide (NaOPh), sodium trifluoroethoxide (NaOCH(2)CF(3)), and sodium butoxide (NaOBu) have been studied. The reaction of 1 and 2 with 4 equiv of NaOPh at 25 degrees C yielded the regioselectively tetrasubstituted species [NSOX{NP(OPh)(2)}(2)] (5d, X = Cl; 6d, X = F). Further reaction of 5d with an additional 2 equiv of NaOPh over several days or at elevated temperatures gave the fully substituted compound [NSO(OPh){NP(OPh)(2)}(2)] (5e), whereas 6d did not react further. The reaction of 1 and 2 with 5 equiv of NaOCH(2)CF(3) yielded in both cases [NSO(OCH(2)CF(3)){NP(OCH(2)CF(3))(2)}(2)] (7e), and similarly reaction with 5 equiv of NaOBu yielded [NSO(OBu){NP(OBu)(2)}(2)] (9e). In all cases, the reactions were monitored by (31)P NMR and (where applicable) (19)F NMR and were found to involve complete substitution at phosphorus via a predominantly vicinal pathway, followed by substitution at sulfur. Substitutional control of the reactions of NaOPh, NaOBu, with 1 and 2 was found to conform to the following general order of reactivity, PCl(2) > PCl(OR) > SOX (X = Cl, F). Although the reaction with NaOCH(2)CF(3) followed the same order of reactivity, a significant enhancement of reaction rate was detected with each equivalent of trifluoroethoxide added. Reaction of 7e with excess NaOCH(2)CF(3) led to elimination of (CF(3)CH(2))(2)O and the formation of the salts Na[NSO(OCH(2)CF(3))NP(OCH(2)CF(3))(2)NP(OCH(2)CF(3))O] (11) and Na[NS(O)O{NP(OCH(2)CF(3))(2)}(2)] (12). Crystals of 6d are triclinic, space group P&onemacr;, with a = 9.789(3) ?, b = 11.393(4) ?, c = 12.079(5) ?, alpha = 107.40(3) degrees, beta = 91.23(3) degrees, gamma = 93.18(3), V = 1283.6(8) ?(3), and Z = 2. Crystals of 5e are monoclinic, space group C2/c, with a = 32.457(3) ?, b = 10.747(1) ?, c = 18.294(2) ?, beta = 110.37(1) degrees, V = 5982.4(9) ?(3), and Z = 8. 相似文献
952.
P. Thibault A. J. Alexander R. K. Boyd 《Journal of the American Society for Mass Spectrometry》1993,4(11):835-844
Angle-resolved translational energy spectroscopy has been applied to Cs4I + 3 ions that survived 8 keV collisions with a range of collision gas targets, including inert gases and deuterium. The experimental data comprise values of the translational energy loss ΔTR as a function of the (laboratory-frame) scattering angle θ R for each collision gas under conditions such that single-collision events dominated the scattering. The values of ΔTR increase with θ R, in accordance with very general expectations. However for any value of θ R, the values of ΔTR for helium and deuterium as targets were almost indistinguishable from one another but were at least five to six times larger than those for neon and all other collision gases. These data have been shown to be consistent with theoretical considerations based upon conservation of energy and linear momentum. Theoretical approaches include the simple “elasticlimit” model, which makes no mechanistic assumptions, and a particular “binary-model” theory, which excludes electronic excitation as a possibility. Both theories are consistent with the experimental data and interpret the surprisingly large values of ΔTR for low-mass targets in terms of large recoil energies of the target required to ensure conservation of momentum. The most likely alternative candidate as sink for ΔTR is internal excitation of the target, but this possibility was excluded in the present work by choosing ΔTR values less than the lowest excitation energies of the inert gas targets. Moreover, such an interpretation cannot explain the similar results obtained using helium and deuterium, which were markedly different from those obtained for all other collision gases. 相似文献
953.
Joseph J. Brophy Vladimir Diakiw Robert J. Goldsack Derek Nelson James S. Shannon 《Journal of mass spectrometry : JMS》1979,14(4):201-203
The appearance of [MH-30]+ ions in the chemical ionization mass spectra of aromatic nitro compounds may be due to their initial reduction to the corresponding amines within the ion source. Aromatic nitroso compounds may be similarly reduced to yield [MH-14]+ ions. The hydroxy derivatives of the nitroso compounds yield further anomalous ions at [MH-16]+ probably due to the reduction of the hydroxy groups. 相似文献
954.
Peter D.W. Boyd Paul M. Johns Clifton E.F. Rickard 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(12):m590-m593
The title compounds, [CuFe2(C5H5)2(C9H8O2)2], (I), and [CuFe4(C5H5)4(C13H9O2)2], (II), are four‐coordinate square‐planar copper(II) complexes with two bidentate 1‐ferrocenylbutane‐1,3‐dionate or 1,3‐diferrocenylpropane‐1,3‐dionate ligands, respectively. The copper ion in (I) lies on an inversion centre, with one‐half of the molecule in the asymmetric unit, while in (II), there are two independent half molecules in the asymmetric unit, with the copper ions also situated on inversion centres. The ferrocene substituents in (I) are in an anti arrangement. The molecules assemble in the crystal structure in layers with ferrocene groups at the surface. The pairs of ferrocene substituents on each ligand in complex (II) are syn and these adopt an anti arrangement with respect to the pair on the other diketonate ligand. As found in (I), complexes assemble in a layered structure with ferrocene‐coated surfaces. 相似文献
955.
The secondary vinylphosphines Ar(F)P(H)C(R)[double bond]CH(2) [2a, Ar(F) = 2,6-(CF(3))(2)C(6)H(3), R = CH(3); 2b, Ar(F) = 2,6-(CF(3))(2)C(6)H(3), R = C(6)H(5); 2c, Ar(F) = 2,4,6-(CF(3))(3)C(6)H(2), R = CH(3)] were prepared by treating the corresponding dichlorophosphine Ar(F)PCl(2) (1) with H(2)C[double bond]C(R)MgBr. In the presence of catalytic base (DBU or DABCO) the vinylphosphines (2a-c) undergo quantitative 1,3-hydrogen migration over 3 d to give stable and isolable phosphaalkenes Ar(F)P=C(R)CH(3) (3a, Ar(F) = 2,6-(CF(3))(2)C(6)H(3), R = CH(3); 3b, Ar(F) = 2,6-(CF(3))(2)C(6)H(3), R = C(6)H(5); 3c, Ar(F) = 2,4,6-(CF(3))(3)C(6)H(2), R = CH(3)). Under analogous conditions, only 90% conversion is observed in the base-catalyzed rearrangement of MesP(H)C(CH(3))[double bond]CH(2) to MesP[double bond]C(CH(3))(2). Presumably, the increase in acidity of the P-H group when electron-withdrawing groups are employed (i.e. 2a-c) favors quantitative rearrangement to the phosphaalkene tautomer (3a-c). Thus, the double-bond migration reaction is a convenient and practical method of preparing new phosphaalkenes with C-methyl substituents. 相似文献
956.
pH-biased isoelectric trapping was used to separate proteins from egg white at the preparative level (80 mg), into discrete protein fractions based on isoelectric point. The problems of isoelectric precipitation that are common for the separation of complex protein mixtures under isoelectric conditions were mitigated by using single-component isoelectric buffers within the sample separation compartments. This combined with the mild process conditions of the Gradiflow unit that was modified for binary isoelectric trapping separations, ensured that biological activity was maintained. This was verified by measurement of the trypsin protease inhibitory activity of the extract and separated fractions. Furthermore, the high resolving power of this system under preparative conditions was demonstrated by separation of three protein isoforms using isoelectric membranes with differences of 0.025 pH units from each other. 相似文献
957.
Boyd J Domene C Redfield C Ferraro MB Lazzeretti P 《Journal of the American Chemical Society》2003,125(32):9556-9557
A significant contribution to the chemical shielding of a nucleus can arise from uniform electric fields that act to distort the electronic charge distribution surrounding a nucleus and, hence, affect the nuclear shielding. It has been shown by Buckingham (Buckingham, A. D. Can. J. Chem. 1960, 38, 300) that the nuclear magnetic shielding tensor sigmaalphabetaI of a nucleus in the presence of an external weak static uniform electric field E may be expanded using sigmaalphabetaI(E) = sigmaalphabetaI + sigmaalphabetagammaIEgamma + 1/2sigmaalphabetagammadeltaIEgammaEdelta + sigmaalphabeta,gammadeltaIEgammadelta ... The third rank tensor sigmaalphabetagammaI is referred to as the dipole-shielding polarizability and describes the nonlinear response of the electron cloud to first order in E, muI, and B0. We report calculations of sigmaalphabetagammaI for the N, HN, and C' nuclei in N-methyl acetamide (NMA) and show that these tensors can be used to provide considerable insight into the behavior of uniform electric fields upon the shielding of backbone nuclei in proteins. The sigmaalphabetagammaI values for the N, HN, and C' of NMA were calculated using the continuous transformation of the origin of the current density (CTOCD) scheme with the diamagnetic contribution set to zero (CTOCD-DZ). Values are given for the individual tensor components of sigmaalphabetagammaI for each nucleus. To test that the calculations have provided a reasonable estimate for the sigmaalphabetagammaI of N, HN, and C' nuclei in proteins, a pH titration was performed using Hen Lysozyme (HEWL). The pH-induced isotropic shielding changes for the C', N, and HN nuclei in some peptide bonds close to E35 ( approximately <8 A) were extracted from sets of fitted titration curves. Assuming the experimental shielding changes arise solely from uniform electric field effects caused by the deprotonation of E35, without any other pH-induced structural alterations which might lead to a shielding change, the experimental shielding differences were compared to those calculated via the product Agamma(I).Egamma where Agamma(I) = (1/3)sigmaalphaalphagammaIota. The agreement with the experimental data is in many cases reasonable and suggests that, within the Buckingham formalism, the complete sigmaalphabetagammaI tensors reported here will be helpful to resolve the importance of uniform electric fields upon isotropic and anisotropic shielding in proteins and their complexes. 相似文献
958.
The solution conformation of trans-2-decalone and the conformational population of cis-2-decalone has been determined by LIS analysis. The angle of pucker (α) of the ketone ring in trans-2-decalone is 51 ± 2°, identical to that of cyclohexanone, but different from that determined for substituted decalones in the solid state, in which significant flattening of the ring occurs.The steroidal conformer of cis-2-decalone, when the latter is complexed to Yb(fod)3 in CDCl3, found to be preferred over the non-steroidal conformer by a ratio of 55:45, in contrast to the preference reported from the low temperature 13C NMR spectrum for the non complexed ketone in CH2Cl2. The two determinations can be combined to give the enthalpy difference in favor of the non-steroidal conformer of ca 0.8 kcal mole?1. 相似文献
959.
Robert J. Helleur Pierre Thibault Joseph H. Banoub Derek H. Shaw 《Journal of mass spectrometry : JMS》1992,27(9):967-973
Application of pyrolysis-desorption chemical ionization mass spectrometry (Py-DCI-MS) is demonstrated for the structural characterization of the native O-specific antigen of Yersinia ruckeri. Under proper pyrolytic and chemical ionization conditions this antigenic polysaccharide yields anhydrohexosamine fragments which facilitate identification of the trimeric repeating unit sequence. Tandem mass spectrometric analyses of the trimeric repeating unit fragments provided additional evidence for the proposed structure and permitted rationalization of the observed fragment ions. Furthermore, Py-DCI-MS of smaller hexosamine subunits isolated during off-line pyrolysis experiments showed fragmentation characteristics almost identical with those observed in the mass spectra of the whole antigen, hence confirming the stability of the pyrolysis fragments. 相似文献
960.
2-Pyridineseleninic anhydride, prepared by oxidation of the corresponding diselenide with iodoxybenzene, is an efficient reagent for the conversion of olefins to unsaturated ketones with retention of the original position of the double bond. This reagent is, therefore, much more reactive towards olefins than benzeneseleninic anhydride. An explanation has been offered. 相似文献