E. Llopis  J.A. Ramirez  A. Cervilla 《Polyhedron》1986,5(12):2069-2074

Polarimetric and spectrophotometric studies of the mannitol-tungsten(IV) system show the formation of three table complexes. Their stoichiometries, degrees of condensation and interconversion equilibria have been studied. The structure of these compounds has been investigated by ¹³C NMR spectroscopy in aqueous solution and by IR spectroscopy in the solid state for the two species stable at pH < 7.  相似文献   

    

Ramirez AA  Linares CJ  Barrero FA  Ceba MR 《Talanta》1986,33(12):1021-1025

Mixtures of La(III) and Mg(II) form with purpurin (P; 1,2,4-trihydroxyanthraquinone) the mixed-metal complex LaMg₂P₅, which is extracted with methyl isobutyl ketone at pH 7.5. The molar absorptivity of the complex is 6.1 × 10⁴ l.mole⁻¹.cm⁻¹ at 570 nm and its conditional extraction constant 5 × 10¹³ l⁴.mole⁻⁴. Similar complexes have been found to be formed with yttrium, cerium, praseodymium, neodymium and samarium. The use of these complexes for the spectrophotometric determination of yttrium and lanthanides up to 15 μg has been investigated.  相似文献   

    

Ronald Callahan  Orlando Ramirez  Kerstin Rosmarion  Robert Rothchild  Kevin C. Bynum 《Journal of heterocyclic chemistry》2005,42(5):889-898

A series of hindered Diels‐Alder adducts have been prepared from phencyclone, 1 , with various unusual symmetrical cyclic dienophiles, including cyclohexene, 2a ; vinylene carbonate, 2b ; vinylene trithiocarbonate, 2c ; and the N‐aryl maleimides: N‐(4‐dimethylamino‐3,5‐dinitrophenyl)maleimide (“Tuppy's maleimide”), 2d ; and N‐[3,5‐bis(trifluoromethyl)phenyl]maleimide, 2e . The highly hindered adducts, 3a‐e , respectively, were extensively characterized by one‐ and two‐dimensional NMR methods, observing proton, carbon‐13 and fluorine‐19. High resolution COSY45 spectra permitted rigorous proton NMR assignments. The 2D heteronuclear C‐H chemical shift correlation spectra (HETCOR, XHCORR) were obtained for adducts 3a‐d , allowing specific assignments for protonated carbons. Corrections to earlier proton NMR assignments for the vinylene carbonate adduct are given; results of the gated decoupling ¹³C NMR experiment for this adduct supported endo adduct stereochemistry. Relative proton chemical shifts for bridgehead phenyls of adduct 3c appeared anomalous relative to other adducts, suggesting possible special anisotropic interactions (with endocyclic sulfur or other anisotropic groups in the product) due to the unusual calculated orientation of the phenyls. The unsubstituted bridgehead phenyls in all adducts were shown to exhibit slow exchange limit (SEL) ¹H and ¹³C spectra on the NMR timescales at ambient temperatures (7 tesla) showing slow rotations about the C(sp³)‐C(aryl sp²) bonds. The rapid rotation of the N‐aryl rings of the maleimide adducts was indicated by fast exchange limit spectra, suggesting that ortho substitution of the N‐aryl ring may be necessary to slow this rotation to the SEL regime. Ab initio geometry optimizations at the Hartree‐Fock level were carried out for each adduct, with the 6‐31G* basis sets. Appreciable geometry differences were seen in calculated structures, and significant NMR chemical shift differences were experimentally observed, depending on the nature of the groups attached to the (Z)‐HC=CH moiety of the dienophiles.  相似文献   

    

M. A. Mora  Laura Galicia  M. A. Mora‐Ramirez 《International journal of quantum chemistry》2004,97(6):983-991

The molecular and electronic structures of 5‐amino‐1,10‐phenanthroline and its monoprotonated and diprotonated species were obtained from ab initio quantum mechanical calculations with unrestricted Hartree–Fock (HF) and Møller–Plesset perturbation theories. The analysis of the net atomic charges and the total spin densities show three possible sites for the monomeric coupling in the polymerization process. The minimal energy conformation for the different kinds of coupling in the formation of the dimers was obtained. The studies were extended to the HF/6‐311 + G(2d,p)//B3LYP (Becke's three‐parameter exchange functional and the gradient‐corrected functional of Lee, Yang, and Paar)/6‐31G(d) level of theory to obtain theoretical nuclear magnetic resonance spectra to study the number and kinds of species involved in the protonation mechanism. Theoretical and experimental nuclear magnetic resonance spectra are in excellent agreement. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004  相似文献   

Structure of 1-acetoxy-1,2-dihydrothiazolo[3,2-a]quinolinium perchlorate     

C. L. Barnes  O. Cox  L. Ramirez  L. A. Bernard 《Acta Crystallographica. Section C, Structural Chemistry》1987,43(9):1739-1742

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Nucleophilic catalysis of phosphorylations by p-nitrophenyldiphenyl phosphate and by alkyl ethylene phosphates in aprotic solvents     

Fausto Ramirez  James F. Marecek 《Tetrahedron letters》1977,18(11):967-970

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Acetate ion catalysis of phosphorylation in aprotic solvents     

Fausto Ramirez  James F. Marecek 《Tetrahedron letters》1976,17(42):3791-3794

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A new synthesis of 5-acylhydantoins, precursors of beta-keto-alpha-amino acids     

F Ramirez  S B Bhatia  C P Smith 《Journal of the American Chemical Society》1967,89(12):3030-3033

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Interaction between shock waves and junctions of two pipes of equal cross section     

A. Dadone  A. Ramirez 《Meccanica》1972,7(1):66-67

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Event-by-event jet quenching     

R. Rodriguez  R.J. Fries  E. Ramirez 《Physics letters. [Part B]》2010

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