Effect of anchimeric assistance in the reaction of triphenylphosphine with α,β-unsaturated carboxylic acids

Quaternization of triphenylphosphine with maleic and cis-aconitic acids is strongly accelerated by participation of the cis-carboxyl group in stabilization of the phosphonium zwitterion intermediate by intramolecular hydrogen bonding, in spite of steric hindrance by the acid's reaction center. A similar effect for trans-isomeric acids is not observed, which can be rationalized on the basis of spatial structures of the generated zwitterions, implying an electrostatic interaction between the phosphonium center and carbonyl oxygen atom. The effect of anchimeric assistance decreases when the intramolecular hydrogen bonding disfavors attack of the phosphine on the sterically less hindered carbon atom of the C=C bond, as observed for cis-aconitic acid. © 2014 Wiley Periodicals, Inc

New Interstellar Extinction Maps Based on Gaia and Other Sky Surveys

We present new three-dimensional (3D) interstellar extinction maps in the $V$ and Gaia $G$ filters within 2 kpc of the Sun, a 3D differential extinction (dust spatial distribution density) map along the lines of sight in the same space, a 3D map of variations in the ratio of the extinctions in the $V$ and Gaia $G$ filters within 800 pc of the Sun, and a 2D map of total Galactic extinction through the entire dust half-layer from the Sun to extragalactic space for Galactic latitudes $|b|>13^{\circ}$. The 3D maps have a transverse resolution from 3.6 to 11.6 pc and a radial resolution of 50 pc. The 2D map has an angular resolution of 6.1 arcmin. We have produced these maps based on the Gaia DR3 parallaxes and Gaia, Pan-STARRS1, SkyMapper, 2MASS, and WISE photometry for nearly 100 million stars. We have paid special attention to the space within 200 pc of the Sun and high Galactic latitudes as regions where the extinction estimates have had a large relative uncertainty so far. Our maps estimate the extinction within the Galactic dust layer from the Sun to an extended object or through the entire dust half-layer from the Sun to extragalactic space with a precision $\sigma(A_\mathrm{V})=0.06$ mag. This gives a high relative precision of extinction estimates even at high Galactic latitudes, where, according to our estimates, the median total Galactic extinction through the entire dust half-layer from the Sun to extragalactic objects is $A_\mathrm{V}=0.12\pm0.06$ mag. We have shown that the presented maps are among the best ones in data amount, space size, resolution, precision, and other properties.Comment: 15 pages, 4 table

Electrical resistivity of liquid CuSn, CuSnBi, CuSnBiIn, CuSnBiInCd alloys of equiatomic compositions

The resistivity of liquid CuSn,CuSnBi, CuSnBiIn, CuSnBiInCd alloys of equiatomic compositions are measured using the rotating magnetic field method to obtain information on their liquid structures. The alloys of equiatomic composition we considered as the high-entropy alloys. The results are discussed in the frame of a microheterogeneous structure of a metallic melt. A conclusion is made about the character of the modification of temperature dependence of the resistivity of liquid alloy due this microheterogeneous structure. All the investigated alloys demonstrated the change in the temperature coefficient of the resistivity for heating and cooling. These changes determined the temperature of destruction the microheterogeneous structure of a metallic melt (T∗). The value of temperature T∗ for all alloys was 1070 K (800 °C). The change in the temperature coefficient of the resistivity of the alloys on heating to 1070 K (800 °C) is interpreted using the Nagel-Tauc model. © 2019 Author(s)

Mechanistic aspects of reactions of triphenylphosphine with electron-deficient alkenes in acetic acid solution

Kinetic data provide evidence that proton transfer to the carbanion centre of a phosphonium zwitterion is the rate-determining step in quarternization reactions of triphenylphosphine with electron-deficient alkenes in acetic acid solution. This conclusion is based on the third-order rate equation, the reactivity of the alkenes, and solvent isotope effects in deuteroacetic acid. Copyright © 2013 John Wiley & Sons, Ltd

Phosphine-catalyzed addition of P(O)-H compounds to ethyl phenylpropiolate

© 2015 Elsevier Ltd. An efficient PBu3-catalyzed α-addition of the P(O)-H bond to ethyl phenylpropiolate has been developed. This strategy offers a facile method for the preparation of synthetically useful alkenyl phosphonates and phosphinates proceeding under neutral reaction conditions with high atom economy