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31.
Cellular algebras 总被引:4,自引:0,他引:4
32.
33.
The thermally stable, terminal phosphinidene complexes [CpM(CO)2(eta1-PNiPr2)]AlCl4(Cp= Cp, Cp*; M = Fe) and [Cp*M(CO)3(eta1-PNiPr2)]AlCl4 (M = Cr, Mo, W) react with Ph2C=N=N to form terminal P-coordinated eta1-phosphaazine and eta3-diazaphosphaallene ligands, respectively, whereas [CpFe(CO)2(eta1-PNiPr2)]AlCl4 reacts with Me3SiCHN2 affording a terminal phosphorus bound eta1-phosphaalkene complex. 相似文献
34.
Graham R. Underwood Brajeswar Paul M. Alice Becker 《Journal of heterocyclic chemistry》1976,13(6):1229-1232
Pyridoxol, protected by acetylation of the hydroxyl groups, has been converted to its N-oxide which upon reaction with perfluoroacetie anhydride yields a 2-nor-2-hydroxymethylpyridoxol derivative as an intermediate. This compound undergoes acyl migration from the 3-position. Protection of the pyridoxol hydroxyls by benzylalion followed by the same treatment yields the unrearranged α2-hydroxy derivative. This compound has been converted to a series of α2-substituted pyridoxols (X = -Cl, -Br, -OCOCH3, -OCH3, -OC2H5). 相似文献
35.
36.
SCF-MS-Xα calculations of the electronic structure of diatomic halogens and interhalogens XY (X = I, Br, Cl; Y = I, Br, Cl, F) have been used to investigate the bonding and nuclear quadrupole coupling in these molecules. Calculations have been carried out for the ground X 1 Σ electronic state, and for the excited B 3 Π0 state in the case of I2, Br2, ICl and IBr. Good agreement (to within 10% in most cases) is obtained between the calculated and observed nuclear quadrupole coupling constants for the molecules in the ground state. For the excited state the agreement is not as good, but the calculation does reproduce the observed decrease in the coupling constants to less than one quarter of their ground state values, and analysis of the contributions to the field gradients clearly shows the reasons for this. The electric dipole moments and electric quadrupole moments of the molecules have also been calculated. However, these prove to be much more strongly dependent on the variables used in the calculation (atomic sphere radii, inclusion of d orbitals). The results of the calculations have also been used to test some of the assumptions made in the Townes and Dailey method of analysis of nuclear quadrupole coupling data. 相似文献
37.
Holliday JD Rodgers SL Willett P Chen MY Mahfouf M Lawson K Mullier G 《Journal of chemical information and computer sciences》2004,44(3):894-902
This paper evaluates the use of the fuzzy k-means clustering method for the clustering of files of 2D chemical structures. Simulated property prediction experiments with the Starlist file of logP values demonstrate that use of the fuzzy k-means method can, in some cases, yield results that are superior to those obtained with the conventional k-means method and with Ward's clustering method. Clustering of several small sets of agrochemical compounds demonstrate the ability of the fuzzy k-means method to highlight multicluster membership and to identify outlier compounds, although the former can be difficult to interpret in some cases. 相似文献
38.
Argouarch G Stones G Gibson CL Kennedy AR Sherrington DC 《Organic & biomolecular chemistry》2003,1(24):4408-4417
Three chiral 2,6-disubstituted tri-N-methyl azamacrocycles have been prepared by modular methods. These macrocycles were accessed from three chiral 1,4,7-triazaheptanes intermediates that were prepared by two independent routes. The first of these routes involved the benzylamine opening of chiral tosyl aziridines followed by debenzylation but was problematic on solubility grounds. A second, more effective, route was developed which avoided debenzylation by using ammonia in the nucleophilic opening of chiral tosyl aziridines. 相似文献
39.
Reaction of Ph3GeLi with [Et4N][HFe3(CO)11] affords the new carbonylferrate salt [Et4N][Ph3GeFe(CO)4] and the same reaction provides an alternative route to the known silicon and tin analogs. Protonation of [Et4N][Ph3GeFe(CO)4] with HCl in ether-THF forms the air-sensitive, thermally rather unstable cis-Ph3GeFeH(CO)4. The latter protonates chloride ions in dichloromethane. 相似文献
40.
Graham DJ 《Journal of chemical information and computer sciences》2002,42(2):215-221
Information in relation to organic molecules was investigated in a previous work (Graham and Schacht, J. Chem. Inf. Comput. Sci. 2000, 40, 187). The topic is given further consideration here with the help of integer statistics. Discussed are the ramifications of an integer variable Omega(t) which quantifies the total number of binding complexions for an organic molecule. Offered is a statistical view of the maximum allowed number of independent regions D expressed by the molecule, dependent on Omega(t). We illustrate the distribution properties of D along with upper limit estimates of the regioinformation mu, also dependent on Omega(t). Integer statistics based on elementary number theory establish the key distribution properties of D and mu. In so doing, the traits distinguishing high regioinformation molecules are enumerated. The statistical approach encompasses all possible molecules and conditions, not just those reported to date in chemical databases. The aim is to view the regioinformation expressed by molecules in an alternative and general way. 相似文献