Sam J. La Placa

Bio: Sam J. La Placa is an academic researcher from Brookhaven National Laboratory. The author has contributed to research in topics: Crystal & Bond length. The author has an hindex of 13, co-authored 15 publications receiving 979 citations.

On a nearly proton‐ordered structure for ice IX

Abstract: Single‐crystal neutron diffraction shows that ice IX, the low‐temperature modification of ice III, has an almost completely proton‐ordered structure in which the ordered component contains two types of water molecules, type 1 in a site of no point symmetry, and type 2 on a twofold axis, each forming four hydrogen bonds in a three‐dimensional framework. The configuration of the water molecules is slightly but significantly altered from that of water vapor. Independent O–D distances, which do not differ significantly from one another, average 0.982± 0.003 A (corrected for thermal motion), and are increased by 0.012 A over the vapor value. The shift in O–D stretching frequency ν1 from vapor to ice IX corresponds to a slope dν1/dr≅ −20 000 cm−1. A−1, which agrees with the slope predicted from spectroscopic anharmonicity constants. D–O–D bond angles (104.7± 0.4°, 106.0± 0.2°) are not decreased from the vapor value (104.5°) despite the smaller O··· O··· O angles into which the water molecules donate protons (98...

Catalytic C−H/Olefin Coupling

Abstract: The cleavage and addition of ortho C−H bonds in various aromatic compounds such as ketones, esters, imines, imidates, nitrile, and aldehydes to olefins and acetlylenes can be achieved catalytically with the aid of ruthenium catalysts. The reaction is generally highly efficient and useful in synthetic methods. The coordination to the metal center by a heteroatom in directing groups such as carbonyl and imino groups is the key. The reductive elimination to form a C−C bond is the rate-determining step.

Agostic interactions in transition metal compounds

Abstract: The impact of agostic interactions (i.e., 3-center-2-electron M-H-C bonds) on the structures and reactivity of organotransition metal compounds is reviewed.