Search

The Valence Bond (VB) model is a physically correct model whereas the Z-model ignores the true origins of the barrier. Even if its quantitative performance appears good within a limited set of reactions, Shaikh et al. prefers to use a correct model and continue to improve its quantitative aspects.

The proposed existence of an alpha-alkane complex on the reaction pathway of either metal insertion into the C-H bond or alkane elimination from the metal center is described. It is shown that complex TpPt(IV)Me(H)2 provides an unprecedented opportunity to study the initial step in the reductive elimination of hydridoalkyl-metal complexes as an isolated kinetic event.

Synthesis of diastereoselective alkylation for products of high diastereomeric excess with predictable stereochemistry is described. The reaction of dianion of methyl (R)-3-hydroxybutyrate generated from LDA with freshly distilled benzyl chloromethyl ether (BOMCI) (1.4 equiv) in THF at -78 degree Celcius was monitored by analytical TLC for 2.5h.

Monomethyl and monoethyl derivatives of acetylhdroquinones are obtained by the reactions of boron trifluoride methyl and ethyl etherate complexes with hydroquinone diesters. This method is a one-step synthesis of acetylhydroquinone derivatives, needed as a building-block for different synthetic applications.

Two new homoscorpionates, Tp(super Me,mt3) and Tp(super Me,Mt4) were prepared, as the first examples of Tp(super x) ligands containing a 3-Me but 5R-substituents other than Me. X-ray crystallography was used to determine the structures of Co[Tp(super Me,mt3)][Tp(super Nt)] and Rh[Tp(super Me,mt4)](COD).

A crystal correlation investigation based on neutron diffraction data has been used to assess the impact of C-H...O interactions on the torsional conformation of methyl groups bonded to C(sp3). There is a clear effect of C-H...O interactions on the torsional conformation of methyl groups.

The optimal conditions for the selective primary mesylation of 1 degree/2 degrees vicinal diol and related systems have been determined. Typical yields of desired monomesylate from reaction of the diol have been as high as 94%. Direct use of the resulting primary mesylate as an electrophile site or conversion to the corresponding terminal epoxide are both accommodated by this method. The representative cases in this study have all proceeded with excellent regioselectivities in the isolated yields.

The coadsorption of CD2I2 and CF3I on the Ag(111) was used to explain migratory insertion of methylene into the metal-carbon bond on a silver single-crystal surface. CH2=CF2 is produced when CH2 is inserted into the Ag-CF3 bond, which then undergoes beta-fluoride elimination to produce liberated fluoroethylene and (CD2=CF2) and adsorbed fluorine. Results affirm the step concerning the propagation of the carbon chain in the Fischer-Tropsch processes. It is the first known example of using a mixture of methylene and perfluoroalkyl groups to illustrate the methylene insertion reaction on a single-crystal surface under ultrahigh-vacuum conditions.

A study was conducted to characterize the synthesis of methyl-substituted conjugate cyclohexenones. The base-catalyzed annulation reaction of beta-keto esters was examined in an effort to come up with a synthetic technique of methyl-substituted conjugate cyclohexenones. Results indicated that mild reaction conditions support simple conjugate enomes that can be utilized in annulation reactions with any polymerization.

The structure of hexamethyltungsten, W[(C[H.sub.3]).sub.6], was determined by x-ray single-crystal diffraction at - 163°C. The molecule has a strongly distorted trigonal prismatic structure with [C.sub.3v] symmetry. This irregular structure is not a result of intermolecular forces, but rather represents its true molecular structure. A similar structure, which deviates less from the ideal trigonal prismatic structure, was determined for hexamethylrhenium, Re[(C[H.sub.3]).sub.6]. Although these structures violate the simplistic models used to predict the geometry of molecules, they are at least in part explainable by the molecular orbital model., Homoleptic molecules, which have only one kind of ligand surrounding a central atom, are important for checking bond theory against experimental data because structure, stability, and reactivity are not influenced [...]

The crystal x-ray diffraction studies of N,N',N''-tris(neopentyl)-1,3,5-triazane reveals that the molecular structure of the compound has one axial and two equatorial neopentyl groups. The groups are found to be eclipsing the equatorial and axial N-CH2 bonds. In solution at very low temperatures 90% or the molecules exhibit this structure and only 9% have an all-equatorial arrangement.

Carbon-13 studies of the mechanism of diamond growth by chemical vapor deposition show that the corrected carbon-13 mole fractions of polycrystalline diamond films and homoepitaxial grown on (100), (110) and (111)natural diamond substrates were each equal to that of methane above the substrate but significantly different from gas-phase acetylene. The methyl radical is concluded to be the predominant growth precursor since carbon-13 mole fractions of methyl radical and methane are nearly identical.

A novel isomerization reaction of the D-ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCo-like proteins (RLPs)) from Rhodospirillum rubrum that converts 5-methylthio-D-ribulose 1-phosphate to a 3:1 mixture of 1-methylthioxylulose 5-phosphate and 1-methylthioribulose 5-phosphate is reported. The disruption observed for the gene encoding the RLP, which abolished the ability of R. rubrum to use 5'-methylthioadenosine as a sole sulfur source, has helped in understanding sulfur salvage.

A novel factor in Caenorhabditis elegans development, the monomethyl branched-chain fatty acid (C17ISO), a product of leucine catabolism is reported. The data obtained sheds light on the role of C17ISO as a chemical/nutritional factor in a mechanism that regulates post-embryonic development in response to the metabolic state of the organism.

The successful alkylations and useful synthetic uses of alpha-trifluoromethyl carbanions like alpha-substituted, beta, beta, beta,-trifluoroethyl, alpha-trifluoromethylethenyl, trifluoroacetimidoyl, alpha-trifluoromethyloxiranyl, and associated alpha-trifluoromethylated carbanions are discussed. It is inferred that alpha-trifluoromethylated carbanions are generally unstable and their stability can be controlled by tuning various factors like hybridization of the orbital that accommodates lone pair electrons.

A molecular dynamics (MD) simulation was used to study the energetics initiating ablation in poly(methyl methacrylate) (PMMA). The simulations showed a decrease in the critical energy when a greater amount of photochemistry is introduced in the system.

Salient aspects on the sources and properties of geosmin and 2-methylisoborneol (2-MIB) that are essential to understanding and managing drinking water mal-odors are reviewed. It is highlighted that some key factors regulating the storage and release of compounds by cells contribute to some of the apparent ambiguity of many taste-and-odor outbreaks.

A biosynthetic pathway from 1,3-bisphosphoglycerate to methoxymalonyl-acyl carrier protein (ACP) is presented. Two new syntheses of R- and S-(1,2-(super 13)C2)glycerol were developed using the proposed pathway.

Triethylamine and 1-methylimidazole (MIM) are the selective catalysts for the Dakin-West synthesis of diaryl ketones and aryl methyl ketones, respectively. A catalyst that can generate an effective acylating agent and a strong base in aprotic solvents will convert anhydrides with only mildly acidic alpha-carbons to aryl methyl ketones, whereas catalysts that cannot facilitate nucleophilic catalysis require more acidic C-H groups for reaction and give diaryl ketones as their major products.

Experiments directed at methyl groups are presented to quantatively analyze rapid structural transitions. This techniques was applied to FKBP12 and small but significant exchange contributions were measured for many methyl [sup.13.C] nuclei.

The results of classical molecular dynamics (MD) simulations and Raman spectroscopy studies of neat liquid N-methylacetamide (NMA), the simplest model system relevant to the peptides, are reported as a function of temperature and pressure. The MD simulations predict that near ambient conditions, the molecules form a hydrogen bond network consisting primarily of linear chains.

Inoculation experiments are performed to study the importance of methylotrophic metabolism for colonization of the model legume Medicago truncatula. Mutants with defects in methylotrophy are capable of plant colonization at the wild-type level, indicating that mutant is not the only carbon source that is accessible to Methylobacterium while it is associated with plants.

The synthesis of chiral methanols [(R)- and (S)-CHDTOH] in a total of 12 steps starting from (chloromethyl)dimethylphenylsilane is described. The chiral methanols are transformed into methyl tosylates used to prepare [(super 2)H1, (super 3)H-methyl]methionines in high overall yields.

Molecular-simulation results for POSS-POSS radial distribution functions (where POSS=polyhedral oligomeric silsesquioxane), potentials of mean force, and self-diffusion coefficients for POSS monomers dissolved in poly(dimethylsiloxane) are presented. Results demonstrate that it is possible to modulate the effective POSS-POSS interaction by increasing the temperature or by substituting by hydrogen atoms in the POSS monomer with methyl groups.

The synthesis, structure solution, and magnetic characterization of four new DIMMAL-containing compounds (H2DIMMAL=2 di1H-2-imidazolylmethylmalonic acid), H2DIMMAL.H2O, Na2(DIMMAL).5H2O, [Cu(HDIMMAL)(sub 2)], and [Cu2(DIMMAL)(sub 2)(H2O2)(sub 2).2H2O is reported. The building-block units described in each case are interconnected into three-dimensional networks by multiple H-bonding paths and aromatic-aromatic interactions.

A study on mechanism of the reaction catalyzed by 2-C-methyl-D-erthritol 4-phosphate (MEP) synthesis from Escherichia coli is studied. The isotope effect with 1-flouro-deoxy-D-xylulose 5-phospheric acid(CF-DXP) and 4S-[(super 2 H)]NADPH but not DXP indicates that the rearrangement step, that precedes hydride transfer, is rate-limiting for DXP but becomes partially rat-limiting for CF-DXP.

The reactions of S-2,4-dinitrophenyl 4-methyl, S-2,4-dinitrophenyl 4-H, S-2,4 dinitrophenyl 4-chloro, and S-2,4-dinitrophenyl 4-nitro thiobenzoates with a structurally homogeneous series of pyridines are subjected to a kinetic investigation in 44 wt % ethanol-water, at 25.0 degree Celsius and an ionic strength of 0.2M (KCI).

A new pi-electronic system with trifluoromethylphenyl groups was developed using the Suzuki coupling reaction. The trifluoromethylphenyl group was found to be very effective in inducing n-type behavior.

The rates of Diels-Alder cycloadditions of anthracenes with methyl vinyl ketone (MVK) are accelerated significantly by the presence of scandium triflate [Sc(OTf)3]. The catalytic effects of Sc(super 3+) salts in the Diels-Alder reaction of MVK are fully compared with the promoting effects of Sc(super 3+) salts in photoinduced electron-transfer reactions.

Oxo alcoxo metallic clusters can be employed as inorganic nanobuilding blocks to obtain well-defined organic-inorganic hybrid materials. It is found that a better understanding of the surface reactivity of these clusters should allow optimization of the elaboration of hybrid materials through a better control of the hybrid interface.

A new optimal total synthesis of demethylasterriquinone B1 was developed that enables the family of methyl scan derivatives to be concisely prepared for evaluation in a cellular assay. The result of this experiment was used to design a biotin-demethylasterriquinone conjugate for use as an affinity reagent.

Reactions of trimethylaluminium, triethylaluminium, and diethylaluminium chloride and ethylaluminium dichloride with silica gel are studied experimentally by infrared spectroscopy and elemental analysis. Infrared spectroscopic studies of the silica gels after reaction indicate that all non-hydrogen-bonded silanols are reacted by all of the reactants under the conditions studied.

The enthalpy of formation of methylhydroxycarbene, CH3COH, is determined from measurements of the threshold energy for collision-induced dissociation of protonated 2,3-butanedione in a flowing afterglow-triple quadrupole mass spectrometer. From the measured enthalpy of formation, the difference between the first and second C-H BDEs in ethanol is found to be 17 kcal/mol, which implies a singlet-triplet splitting of 28 kcal/mol in the carbene.

The reactions of a series of Pd(II) methyl compounds of general formula LPd(NCCH(sub 3))CH(sub 3), where L is bulky phenoxydiazene or phenoxyaldimine ligand with the polar olefin acrylonitrile (AN), are reported. It is concluded that the rates of insertion in both of the complexes are significantly faster than reported rates for analogous reactions in cationic in Pd(II) derivatives, indicating that increasing the negative charge on the complex enhances the rate of AN insertion.

Density functional based numerical approaches for computing orbital and atomic reactivity indices are employed in the study of selectivity descriptors for the 1,4 Michael addition reaction. It is shown that the methods employed for local reactivity index computations are useful and reliable for prediction of the regioselectivity upon conjugate addition of ambident nucleophiles to 2,3-unsaturated carboxylic esters.

The temperature dependence of methyl group dynamics predicted by molecular dynamic (MD) simulations of a protein over a range of temperatures spanning the dynamical transition, with and without aqueous solvent is reported. The results confirm that the solvent is required for the dynamical transition and also demonstrate that the transition is accompanied by an abrupt increase in mobility throughout most of the protein.

The conversion of sterically hindered carboxylic acids to N-methoxy-N-methyl amides can be efficiently carried out with 1.1 equiv of methanesulfonyl chloride, 3 equiv of triethylamine, and 1.1 equiv of N-methoxy-N-methylamine. N-methoxy-N-methylmethanesulfonamide, the major byproduct for these reactions, can be removed by placing the product mixture under vacuum for 14-24 hours.

Methyl substituents on the distant benzene ring of the dppz ligand in [Ru(phen)(sub 2)dppz](super 2+) strongly diminish solvent hydrogen bonding to the excited state due to entropy. The effects of methyl substitution are smaller when the complexes are intercalated into DNA, suggesting that the water molecules that quench the excited-state access the aza nitrogens of the dppz ligand from the groove where the Ru(II) ion resides.

The regiospecific reaction of bis(pinacolato)-diborane (B2oin2) and pinacolato)-C-H bonds of alkanes catalyzed by Cp*Rh(eta(super 4)-C6Me6 is reported. The products from these reactions can be converted directly from the crude reactions to alcohols, alkylarenes, and alkyltrifluoroborates.

Pulse radiolysis of aqueous solutions of alpha-(methylthio)acetamide produced large quantities of acetamide radicals that were identified by time-resolved electron spin resonance (TRESR) spectroscopy. The pH dependence of the TRESR-measured radical yields results from selective scavenging reactions, and density functional theory predictions of the reaction thermochemistry demonstrate that bimolecular homolytic substitution, S(sub H)2, of the acetamide radical is the most likely formation pathway.

The design of a photoreactive AMPA (alpha-amino-3-hydroxy-methyl-4-isoxazole) receptor antagonist is described. It provides a means of photochemically 'knocking out' AMPA receptors in living cells.

Subtle features of (super 13)C NMR spectra of perdeuterated methyl groupings are discussed. The study revealed that the (super 13)C line shape is dependent upon both the scalar coupling between magnetically equivalent deuterons and deuteron autocorrelated, and cross-correlated quadrupolar spectral densities.

A fully-dimensionality direct ab initio dynamics study is carried out to understand the detailed reaction mechanism for O [(super 1) D] + CH4 reaction. It was noticed that the direct reactions for the products OH and CH3 proceed through an insertion mechanism to form a very short-lived vibrationally excited CH3OH molecule.

The thermal chemistry of iodomethane on Ni(110) single-crystal surfaces is studied. It is shown that the hydrogenation step of methyl methane is controlled by the population of surface hydrogen.

The dynamics of H-atom abstraction reactions of Cl atoms with CH3Cl and CH3Br are studied using velocity map imaging to obtain center-of-mass frame differential cross sections for HCL formed in its vibrational ground state and rotational levels with J= 2-5. The HCL products are preferentially backward scattered in both reactions, with broad angular distributions of velocities that extend to sideways and forward scatter, and which show almost no variation with J.