Isotopes Lewis structures

Lewis made additional valuable contributions to the theory of colored substances, radiation, relativity, the separation of isotopes, heavy water, photochemistry, phosphorescence, and fluorescence. As a major in the U.S. Army Chemical Warfare Service during World War I, he worked on defense systems against poison gases. From 1922 to 1935 he was nominated numerous times for the Nobel Prize in chemistry. Lewis s death, while measuring the dielectric constant of hydrogen cyanide on March 23, 1946, precluded his receiving the prize, which is not awarded posthumously, see also Acid-Base Chemistry Lewis Structures. 

Gilbert Newton Lewis (1875-1946 was born in Weymouth, Massachusetts, and received his Ph.D. at Harvard in 1899. After a short time as professor of chemistry at the Massachusetts Institute of Technology (1905-1912), he spent the rest of his career at the University of California at Berkeley (1912-1946). In addition to his work on structural theory, Lewis was the first to prepare heavy water," D20, in which the two hydrogens of water are the 2H isotope, ceuterium. 

The discovery happened by accident. Lewis and Anders were frustrated by their failure to find the carrier of anomalous xenon in carbonaceous chondrites. They decided to try an extreme treatment to see if they could dissolve the carrier. They treated a sample of the colloidal fraction of an Allende residue with the harshest chemical oxidant known, hot perchloric acid. The black residue turned white, and to their surprise, when they measured it, the anomalous xenon was still there The residue consisted entirely of carbon, and when they performed electron diffraction measurements on it, they found that it consisted of tiny (nanometer sized) diamonds. After a detailed characterization that included chemical, structural, and isotopic studies, they reported the discovery of presolar diamond in early 1987 (Lewis et al., 1987). The 23-year search for the carrier of CCFXe (Xe-HL) was over, and the study of presolar grains had begun. 

Quantum mechanical calculations show that the silyl cation (19) has a twisted structure, and that the a-C02 group provides substantial electrostatic stabilization.58 Isotope effects for its formation reaction are also reported.58 Evidence is provided for the stabilization of incipient oxocarbenium ions by axial electronegative substituents, as in (20) the presence of the most electronegative substituent results in the fastest reaction.59 Lewis acid-promoted cleavage of spirocyclic dioxanes such as (21) involves oxonium ions, and high axial vs equatorial product selectivities are possible with the correct choice of Lewis acid and nucleophile.60 Reactions which lead to 1,3-dioxenium salts have been reviewed.61... 

In 1933, Erdtman suggested [20] that the basic lignan structure involved the coupling of two phenylpropanoid monomer units. Isotope tracer experiments on lignans were later described [2,21,22]. Significant advances have however been made in the chemistry and biosynthesis of lignans by Lewis... 

Zinner E., Amari S., Wopenka B., and Lewis R. S. (1995) Interstellar graphite in meteorites isotopic compositions and structural properties of single graphite grains from Murchison. Meteoritics 30, 209-226. 

Catalytic reactions of hydrocarbons over zeolites are reviewed. The historical development of various mechanistic proposals, particularly of the carbonium ion type, is traced. In spite of numerous catalytic, spectroscopic, and structural studies which have been reported concerning the possible roles of Bronsted acid, Lewis acid, and cationic sites, it still is not possible to formulate a comprehensive mechanistic picture. New activity and product data for cumene cracking and isotope redistribution in deuterated benzenes over Ca-and La-exchanged Y zeolites is presented. Cracking of the isomeric hexanes over alkali metal-exchanged Y and L zeolites has been studied. This cracking is clearly radical rather than carbonium-ion in nature but certain distinct differences from thermal cracking are described. 

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