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Showing papers in "Journal of the American Chemical Society in 1981"


PatentDOI
TL;DR: In this article, a metal alkoxide is used as a catalyst, where the metal has a coordination number of at least four, and at least one, usually two, of the alkoxide groups bonded to the metal are bonded to asymmetric carbon atoms.
Abstract: OF THE DISCLOSURE Methods and compositions are provided for asymecrically donating an oxygen atom to a pair of electrons to produce an asymmetric product. Specifically, a metal alkoxide is used as a catalyst, where the metal has a coordination number of at least four, and at least one, usually two, of the alkoxide groups bonded to the metal are bonded to asymmetric carbon atoms. The metal catalyst is employed in conjunction with a hydroperoxide and an alkanol having a functionality with a pair of electrons capable of accepting an oxygen atom. The resulting product is enriched in one enantiomer due to the enantioselective introduction of an asymmetric center or an enhanced rate of reaction of one of the enantiomers of a chiral alkanol. Greatly enhanced yields of enantiomers are achieved as compared to prior enantioselective introduction of oxygen. This invention was made at least in part in the course of a grant from the U.S. National Institutes of Health (GM24551).

2,306 citations




Journal ArticleDOI
TL;DR: Transferable intermolecular potential functions (TIPS) suitable for use in liquid simulation are reported for water, alcohols, and ethers as discussed by the authors, where interaction sites are located on oxygens, hydroxyl hydrogens, and the carbons in alkyl groups.
Abstract: Transferable intermolecular potential functions (TIPS) suitable for use in liquid simulation are reported for water, alcohols, and ethers. Interaction sites are located on oxygens, hydroxyl hydrogens, and the carbons in alkyl groups. Each type of site has Coulomb and Lennard-Jones parameters chosen to yield reasonable structural and energetic results for both gas-phase dimers and pure liquids. A Monte Carlo simulation of liquid water at 25/sup 0/C using the TIP potential compares favorably with experiment or results from Clementi's CI potential except that the OO radial distribution function is calculated to be too flat beyond the first solvent shell. Simulations of liquid methanol and ethanol have also been carried out as described in the accompanying papers. Overall, in view of the simplicity and transferability of the potentials, the initial results are most encouraging for the treatment of fluids with even more complex monomers and for extension to other types of interaction sites.

1,061 citations











Journal ArticleDOI
TL;DR: In this article, it was demonstrated that the buildup rates of the nuclear Overhauser effect can be measured by two-dimensional NMR spectroscopy with the basic pancreatic trypsin inhibitor.
Abstract: It is demonstrated, by means of experiments with the basic pancreatic trypsin inhibitor, that the buildup rates of the nuclear Overhauser effect can be measured by two-dimensional NMR spectroscopy. Qualitative correlations between the buildup rates of first-order Overhauser effects, which arise from direct dipole-dipole coupling between closely spaced protons, and the proton-proton distances in the protein conformation are established. Second-order Overhauser effects due to spin diffusion by cross-relaxation between more distant protons are also identified. On the basis of these observations, potentialities and limitations of two-dimensional nuclear Overhauser enhancement spectroscopy for studies of the conformation of biological macromolecules are discussed and suggestions made for improved experimental procedures. For quantitative measurements of Overhauser effects, the use of phase-sensitive spectra and of techniques for selective suppression of J cross-peaks in data sets recorded with very short mixing times appears particularly important.


Journal ArticleDOI
TL;DR: In this paper, a theory of charge transfer stabilization of the transition state for nucleophilic addition to a carbonyl group by electron donors is proposed, using the Bell-Evans-Polanyi principle.
Abstract: A theory of charge-transfer stabilization of the transition state for nucleophilic addition to a carbonyl group by electron donors is proposed. It is postulated, using the Bell-Evans-Polanyi principle, that the feature of this transition state critical for stereoselectivity of the reaction is the existence of a low-lying vacant orbital u** associated with the u bond being formed in the reaction and that electron delocalization into that orbital will stabilize the transition state and may thereby enhance the reaction rate: the kinetic anomeric effect and the kinetic a effect are considered as the examples of such a stabilizing interaction. Stereochemistry of nucleophilic addition to cyclohexanone is determined by two factors according to this model: steric hindrance which favors the equatorial approach and electron donation from the cyclohexanone ucc and ucH bonds into the u** orbital, which favors the axial approach since the carbon-hydrogen bonds are better electron donors. Consequently, nucleophile structure, metal cations complexing the carbonyl oxygen, solvent, and counterions or other solutes may influence stereoselectivity of the reaction by changing the e(.**). Furthermore, it is shown that this model offers a simple and consistent way to rationalize kinetic and stereochemical effects of the so-called "remote polar substituents" which cannot be explained in terms of steric or electrostatic interactions but appear to be controlled by the overlap and energy gap between the remote electron-donor orbitals and the u** orbital.

Journal ArticleDOI
TL;DR: In this article, an aqueous system for electrogenerated chemiluminescence (ecl) based on the reaction of electregenerated Ru(bpy),'+ with strong reductants produced as intermediates in the oxidation of oxalate ion is described.
Abstract: An aqueous system for electrogenerated chemiluminescence (ecl) based on the reaction of electrogenerated Ru(bpy),'+ with strong reductants produced as intermediates in the oxidation of oxalate ion is described. The bright orange chemiluminescence, which could also be generated by reaction of chemically produced Ru(II1) species with oxalate, corresponded to emission by R~(bpy)~*+*; ecl efficiency (photons emitted/R~(bpy)~~+ generated) was -2% in deaerated solution. Ecl by reaction of the 1+ and 3+ Ru species could also be obtained in partially aqueous solutions containing at least 20% acetonitrile. Chemiluminescence was also observed with other organic acids (pyruvic, malonic, lactic), when the intermediates produced on their oxidation by Ce4+ reacted with R~(bpy),~+.

Journal ArticleDOI
TL;DR: In this article, the authors present a Web of Science Record created on 2006-02-21, modified on 2017-05-12, with the purpose of improving the quality of the record.
Abstract: Reference LPI-ARTICLE-1981-026doi:10.1021/ja00406a004View record in Web of Science Record created on 2006-02-21, modified on 2017-05-12








Journal ArticleDOI
TL;DR: The role of the surface CH/sub 2/ species in the conversion of CO and HO to hydrocarbons is used to evaluate the correctness of the Fischer-Tropsch, Pichler-Schultz, and the Anderson-Emmett schemes as discussed by the authors.
Abstract: The role of the surface CH/sub 2/ species in the conversion of CO and H/sub 2/ to hydrocarbons is used to evaluate the correctness of the Fischer-Tropsch, Pichler-Schultz, and the Anderson-Emmett schemes. CH/sub 2/N/sub 2/ was used to add CH/sub 2/ groups to the cobalt catalyst surface; this resulted in an increased production of higher molecular weight molecules as predicted only by the Fischer-Tropsch scheme. Distributions of /sup 13/C atoms in the propene formed when a mixture of /sup 13/CO, H/sub 2/, and /sup 12/CH/sub 2/N/sub 2/ were passed over the catalyst, also confirmed the Fischer-Tropsch scheme. (DLC)

Journal ArticleDOI
TL;DR: Two-dimensional NMR techniques which sep. the chem. shift and heteronuclear dipolar interactions were applied to samples spinning at the magic angle as mentioned in this paper, and rotational echoes were obsd. in the time domain of each dimension.
Abstract: Two-dimensional NMR techniques which sep. the chem. shift and heteronuclear dipolar interactions were applied to samples spinning at the magic angle. Because of the inhomogeneous nature of the 2 interactions, rotational echoes were obsd. in the time domain of each dimension. The corresponding Fourier transforms yield rotational sideband spectra which provide information on the principal values and relative orientations of the shift and dipolar tensors, and from the latter, internuclear distances may be calcd. The techniques therefore provide a means for obtaining structural data, for example, 13C-1H and 15N-1H distances, in powder samples. [on SciFinder (R)]