Hoffmann studies

Wynder, E.L. and D. Hoffmann Studies with the gaseous and particulate phase of tobacco smoke Proc. Am. 4332. 

Stowasser and Hoffmann studied recently the single-particle orbitals for some few smaller systems using different theoretical methods.58 In Figure 11 we show their results for the water molecule as obtained with a GGA method and with Hartree-Fock calculations. The orbitals are indeed very similar, supporting the idea that one may analyse the Kohn-Sham orbitals as electronic orbitals. 

S. Metzer and R. Hoffmann, Studies on dephosphorylation of phosphotyrosine-containing peptides during post-source decay in matrix-assisted laser desorption/ion-ization, 7. Mass Spectrom. 35, 1165-1177 (2000). 

The multifunctional nature of Cinchona alkaloids makes them especially prone for a complex reactivity that occurs with a degradation or rearrangement of the carbon moiety, often controlled by the stereochemistry of the particular alkaloid. These characteristic for Cinchona alkaloid transformations include an acid-catalyzed formation of cinchotoxines 59 described as early as in 1853 by Pasteur [108] or synthesis of diverse cyclic ethers, for example, )S-isoquinidine 60 or jS-isocupreidine 61, bearing oxazatwistane moiety [180, 201, 202] (Scheme 21.5). This can be used as an efficient catalyst of a stereoselective Baylis-HiUman reaction [8-10, 203, 204]. Hoffmann studied in detail the two distinct cage rearrangements... 

K. Fukui (Kyoto) and R. Hoffmann (Cornell) quantum mechanical studies of chemical reactivity. 

UV irradiation. Indeed, thermal reaction of 1-phenyl-3,4-dimethylphosphole with (C5HloNH)Mo(CO)4 leads to 155 (M = Mo) and not to 154 (M = Mo, R = Ph). Complex 155 (M = Mo) converts into 154 (M = Mo, R = Ph) under UV irradiation. This route was confirmed by a photochemical reaction between 3,4-dimethyl-l-phenylphosphole and Mo(CO)6 when both 146 (M = Mo, R = Ph, R = R = H, R = R" = Me) and 155 (M = Mo) resulted (89IC4536). In excess phosphole, the product was 156. A similar chromium complex is known [82JCS(CC)667]. Complex 146 (M = Mo, R = Ph, r2 = R = H, R = R = Me) enters [4 -H 2] Diels-Alder cycloaddition with diphenylvinylphosphine to give 157. However, from the viewpoint of Woodward-Hoffmann rules and on the basis of the study of UV irradiation of 1,2,5-trimethylphosphole, it is highly probable that [2 - - 2] dimers are the initial products of dimerization, and [4 - - 2] dimers are the final results of thermally allowed intramolecular rearrangement of [2 - - 2] dimers. This hypothesis was confirmed by the data obtained from the reaction of 1-phenylphosphole with molybdenum hexacarbonyl under UV irradiation the head-to-tail structure of the complex 158. 

The elegant, enantiospecific synthesis of biotin (1) by Hoffmann-La Roche1 is based on a strategy that takes advantage of the powerful intramolecular nitrone-olefin cycloaddition reaction. Our analysis begins with model studies in which the straightforward conversion of L-cysteine (2) into aldehyde 3 (see Scheme 1) constitutes... 

P-coupling occurs in the formation of azophosphonic esters [ArN2PO(OCH3)2] from diazonium salts and dimethyl phosphite [HPO(OCH3)2] (Suckfull and Hau-brich, 1958). P-coupled intermediates are formed in the reaction between diazonium salts and tertiary phosphines, studied by Horner and Stohr (1953), and by Horner and Hoffmann (1956). The P-azo compound is hydrolyzed to triphenylphosphine oxide, but if a second equivalent of the tertiary phosphine is available, phenyl-hydrazine is finally obtained along with the phosphine oxide (Scheme 6-26 Horner and Hoffmann, 1958). It is likely that an aryldiazene (ArN = NH) is an intermediate in the hydrolysis step of the P-azo compounds. 

Recently, a study of this rearrangement has been repeated and extended in order to determine the influence of a- and y-substitution on the position of the 68-69 equilibrium in the presence of silica, and the utility of this reaction for a novel and convenient synthesis of highly substituted a, / -unsaturated ketones, by subsequent treatment with CuCl2 in methanol-water136. An ion-pair mechanism can also be suggested for the facile rearrangement of sulfone 70 to 71, a key intermediate in the Hoffmann-La Roche Sulfone Route to Vitamin A137. 

Wynder, E.L. Hoffmann, D. "Tobacco and Tobacco Smoke -Studies in Experimental Carcinogenesis." Academic Press, New York, 1967, p. 730. 

After having described molybdenum trioxide, we intend to specify the best finite clusters allowing to represent each of the (010), (001) and (100) faces in order to study surface properties such as energy and electronic distribution. For this purpose, the evolution of the electronic properties will be studied as a function of the cluster size and referred to the results of an EHT - band calculation [12] all calculations have been made with QCPE programs [13,14] and Hoffmann parameters [15],... 

Stahl, M., Schopfer, U., Frenking, G., Hoffmann, R. W., 1997, Conformational Analysis with Carbon-Carbon Coupling Constants. A Density Functional and Molecular Mechanics Study , J. Org. Chem., 62, 3702. 

Hoffmann U, Segerer S, Rummele P, et al. Expression of the chemokine receptor CXCR3 in human renal allografts—a prospective study. Nephrol Dial Transplant 2006 21 1373-1381. 

King, Lester S. Stahl and Hoffmann a study in eighteenth-century animism. JHist Med Allied Sci 19(1964) 118-130. 

Perhaps the first evidence for the breakdown of the Born-Oppenheimer approximation for adsorbates at metal surfaces arose from the study of infrared reflection-absorption line-widths of adsorbates on metals, a topic that has been reviewed by Hoffmann.17 In the simplest case, one considers the mechanism of vibrational relaxation operative for a diatomic molecule that has absorbed an infrared photon exciting it to its first vibrationally-excited state. Although the interpretation of spectral line-broadening experiments is always fraught with problems associated with distinguishing... 

Vanparys P, Schechtman L, Aardema M, Hayashi M, Hoffmann S, Gribaldo L, Corvi R (2010) Balb/c 3T3 Cell Transformation Assay - Prevalidation Study Report. ECVAM Balb/c 3T3 CTA PRP report vl - 30 July 2010... 

Bulo et al. <2004AG732> have studied the degenerate rearrangements that occur among bicyclic hydrocarbons with three-membered rings. Extending the work to include phosphorus resulted in the formation of compound 197. Compound 198 was heated to 50 °C and the Woodward-Hoffmann-allowed product for a [ l,5]-shift (compound 199) was produced (Scheme 17). 

Carbene Complex Geometries. Molecular orbital studies of the various conformations of several transition metal-carbene complexes have been undertaken by the groups of Fenske and Hoffmann (8,13). Of the two... 

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