This student is interested in reinvestigating the kinetics and mechanism of the bridged compound in l,2-dichloroethane with triisopropyl phosphite and in finding the reasons why the values of competition ratio k₋₂ /k₃ in this reaction are so large.

The reactivity of the [(Phen)Cr(CO)_3] intermediate with phosphines and phosphites (L) has been investigated through ligand-competition studies. This intermediate possesses virtually no ability to discriminate among L. The agreement between reactivity data for the thermal and photochemically-generated intermediates indicates that the same intermediate is produced via each process. Pulsed laser flash photolysis of (n^2-NP)M(CO)_4 (I) (M = Cr, Mo; NP = 1-diethylamino-2-diphenylphosphinoethane) in the absence and presence of P (OPr-i)_3 (L) in 1,2-dichloroethane and chlorobenzene induces unimolecular ring-opening to afford [(n^1-NP)M(CO)_4] (II), in which the bidentate ligand is coordinated through P. Reaction of this intermediate takes place through competitive ring-reclosure and attack at (II) by L to afford (I) and cis-(n^1-NP) (L)M(CO)_4.

The substitution reaction of (DTN)W2 (CO)10 with P(OCH(CH3 )2 )3 is a stepwise reaction. The kinetics of step 1 follow the equation: -d[substrate] /dt = kld [substrate] + k la [substrate] [ligand]. Thus the mechanism of step 1 is expected to be a competition between dissociative and associative pathways. The kinetics of step 2 follow the equation: -d[(DTN)W(CO)5]/dt = k2dk3[(DTN)W(CO)5][ligand]/k-2[DTN] + k3[ligand] The plot of kobsd versus [ligand] thus is a hyperbolic curve and the plot of 1/kobsd versus 1/[L] exhibits linear behavior. A mechanism for step 2 in which (DTN)W(CO)5 dissociates to an intermediate, W(CO) 5 , and in which DTN and P(OCH(CH3 )2 )3 compete to associate with W(CO) 5 is favored. The dissociative rate constant of the first step, kld' is about 1.2 times of that of the second step, k2d. The dissociation of (DTN)W(CO) 5 from (DTN)W2 (CO) 1 0 is favored over the dissociation of DTN from (DTN)W(CO) 5 due to a combination of the steric, stoichiometric, charge repulsion and entropy effects of the reaction.

The glyoxalase system, which has been known since 1913, is widely distributed in nature. The system consists of two enzymes, glyoxalase I and glyoxalase II. Methylglyoxal is very unstable and undergoes oxidation and polymerization reactions. One of the purposes of this study was to find a simple, convenient and reproducible method of methylglyoxal preparation. Another objective was the purification of both glyoxalase enzymes employing affinity chromatography as a major step. The purified enzymes were to be characterized by chemical, physical and kinetic properties as an approach to the understanding of the biological function of the system.

Thermal and flash photolysis studies of ligand-substitution reactions of cis-(pip)(L)M(CO)_4 by L' (pip = piperidine; L, L' = CO, phosphines, phosphites; M = Cr, Mo) implicate square-pyramidal [(L)M(CO)_4], in which L occupies a coordination site in the equatorial plane, as the reactive species. In chlorobenzene (= CB) solvent, the predominant species formed after flash photolysis and a steady-state intermediate for the thermal reaction is cis—[(CB)(L)M(CO)_4], for which rates of CB-dissociation increase with increasing steric demands of coordinated L. Rates of CB-dissociation from trans-[(CB)(L)M(CO)_4] intermediates, formed after photolysis but not thermally, exhibit no observable dependence on the steric properties of the coordinated L.

Pulsed laser time-resolved ligand-substitution photochemistry for (DTO)W(CO)4, (DTN)W(CO)4, and (NP)Mo(CO)4 (DTO = 2,2,7,7-tetramethyl-3,6-diathiaoctane; DTN = 2,2,8,8- tetramethyl-3,7-diathianonane; NP = l-diethylamino-2- diphenylphosphinoethane) proceeds via initial fission of the W-S and Mo-P bonds, affording Cs and C4v five-coordinate intermediates for DTN and NP but largely Cs for DTO. The rates of reaction of these intermediates, via chelate ring closure and competitive bimolecular interaction with Lewis bases (= L, alkylphosphines and alkyl phosphites) for the Cs intermediates and via bimolecular interaction of L with the C4v intermediates, together with activation parameters for these processes have been determined. The rates of interactions at the Cs intermediates are significantly faster than at the C4v intermediates.

The conformational energy differences have been determined for ethylene glycol, 2- chloroethanol, and 2,2- dichloroethanol in the neat liquid, DMSO, and H20 with Raman spectroscopy. Spectra in the 0-H valence region were utilized to determine the energy difference between interand intramolecularly hydrogen bonded species. It was found that the solvent effect on the relative stabilities of the gauche and trans rotamers of the alcohols differ significantly. The results also indicate that, unlike ethylene glycol, there is significant intramolecular hydrogen bond formation in the halogenated alcohols in the neat liquid phase. Stronger intramolecular hydrogen bond formation was observed in dichloroethanol than in 2-chloroethanol.

The reaction of chlorodimethylvinylsilane with tertbutyllithium was investigated in the presence of several conjugated dienes. In all cases except with 2,5-dimethylfuran, [2+4] cycloadducts of a silene intermediate are obtained in hydrocarbon solvents. The presence of THF in the reaction mixture suppresses the formation of cycloadducts in favor of 1,3-disilacyclobutanes. In the reaction of dimethylethoxyvinylsilane or dimethylmethoxyvinylsilane with tert-butyllithium the main product is the 1,1-dimethyl2-neopentyl-4-(dimethylalkoxysilyl)silacyclobutane. It is concluded that lithium chloride elimination to give silene intermediates occurs in hydrocarbon solvents. In the presence of strong Lewis bases or when the leaving group on silicon is an alkoxy group, the addition reaction giving a-lithiosilanes occurs and products arising from their coupling reactions are obtained.

Thermal reactions and flash photolysis are used to study the olefin bond-migration promoted by tungsten carbonyls. Substitution of piperidine (pip) by 2- allylphenyldiphenylphosphine (adpp) in the cis-(pip)(η^1- adpp)W(CO)-4 complex was investigated, and no olefin bond-migration was observed. This suggests that a vacant coordinated site adjacent to the coordinated olefin is an essential requirement for olefin bond rearrangement. The rates of olefin attack on the photogenerated coordinatively unsaturated species, cis-[(CB)(η^1-ol- P)W(CO)-4] (CB = chlorobenzene, p-ol = Ph-2P(CH-2)-3CH=CH-2; n = 1-4) were measured. Kinetics data obtained both in pure CB and in CB/cyclohexane mixtures support a dissociative mechanism in which the W-CB bond is broken in the transition state. In contrast to results observed in studies of other related systems, no olefin bond-migration is noted. This observation is attributed to P-W coordination at all stages of the reaction, which precludes formation of a reactive intermediate containing a vacant coordination site adjacent to a P-ol bond.

Dimethylsilene, generated from the thermal gas phase reaction of 1,1-dimethyl-1-silacyclobutane, reacts with alkynes to produce silacyclobutenes or acyclic silanes. The temperature dependence of the product ratios have been determined and the relative reactivities of three different alkynes toward the 1,1-dimethylsilene has been determined. 1-Hydrido-1-methylsilene has been generated by gas phase thermal decomposition from three different precursors. Trapping studies with butadiene and trimethylsilane lead to products expected from dimethylsilylene. The most plausible explanation for these observations is that hydridomethylsilenes undergo a facile isomerization to divalent dimethylsilylene. Cycloaddition of 1,1-dimethylsilene to allene at 600°C in a flow vacuum pyrolysis system affords the first synthesis of 2-methylene-1,1-dimethylsilacyclobutane and smaller amounts of six other products. For static pyrolysis at 421°C, the 2-methylene-1,1-dimethyIsilacyclobutane isomerizes to 1,1-dimethylsilacyclopentenes. The kinetics of gas phase thermal decomposition of cyclopropyltrimethylsilane has been studied over the temperature range, 689.6-751.1 K at pressures near 14 torr. The Arrhenius parameters for formation of allyltrimethylsilane are k_1(sec^-1)=10^14.3 ± 0.1 exp(-56.5 ± 0.2 kcal mol^-1/RT) and those for the formation of E- and Z-1-propenyltrimethyIsilane are k_2(sec^-1)=10^14.9 ± 0.3 exp(-61.9 ± 0.8 kcal mol^-1/RT). The difference between activation energies has been interpreted in terms of anchimeric assistance or the β effect of the silicon atom. The …

The induced circular dichroism (ICD) of several chiral nitrosamines and various chiral reagents has been investigated. The interaction is attributed to a 1:1 hydrogen bonded complex between the NO group of the nitrosamine and the hydroxyl groups of alcohols and polyols, or the amino group of amines. Only those chiral reagents possessing large differences in size of the groups about the hydrogen bonding site contributed to CD anomalies. The acyclic 2-octanols did not give observable Cotton effects, presumably due to the similarity in size of the methyl and methylene groups and rotational freedom of the acyclic system. The signs of the Cotton effects could be correlated with the absolute configuration of the sterically hindered alcohols and amines. Only the alpha, axial hydrogens of conformationally biased, heterocyclic nitrosamines were found to undergo selective hydrogen-deuterium exchange, suggesting that this feature is critical for nitrosamine carcinogenicity.

The purpose of this investigation is to examine reactions of anions of oximes, oxime ethers and imines with acylating agents and other electrophiles. It is also an attempt to utilize the phenomenon of geometrical enantiomeric isomerism, in which absolute configuration is determined by double bond geometry, and the concept of regiospecific anion formation, also determined by double bond geometry, for stereospecific synthesis of tropinone derivatives.

High Performance Liquid Chromatography (HPLC) was used to investigate the utility of this technique for the analytical and preparative separation of components of aquatic fulvic acids (FA). Three modes of HPLC namely adsorption, anion exchange and reversed phase were evaluated. Aquatic fulvic acids were either extracted from surface water and sediment samples collected from the Southwest of the U.S., or were provided in a high purity form from the USGS. On the adsorption mode, a major fraction of aquatic fulvic acid was isolated on a semipreparative scale and subjected to Carbon-13 NMR and FAB Mass Spectroscopy. Results indicated that (1) The analyzed fraction of fulvic acid contains more aliphatic than aromatic moieties; (2) Methoxy, carboxylic acids, and esters are well-defined moieties of the macromolecule; (3) Phenolic components of the macromolecules were not detected in the Carbon-13 NMR spectrum possibly because of the presence of stable free radicals. Results of the anion exchange mode have shown that at least three types of acidic functionalities in aquatic fulvic acid can be separated. Results also indicated that aquatic fulvic acid can be progressively fractionated by using subsequent modes of HPLC. Results of reversed phase mode have shown that (1) The fractionation of aquatic …

The physico-chemical properties of lecithin:cholesterol acyltransferase were investigated. The amino acid composition analysis showed a relatively high content of glutamic acid, aspartic acid, glycine and leucine. The spectrophotometric titration of phenolic groups in the enzyme showed a large increase in absorbance at 295 nm with an apparent pK of about 12.0. The largest change in molar ellipticity at 222 nm was also observed above pH 11. Circular dichroism studies revealed that human lecithin:cholesterol acyltransferase has a relatively high content of β-pleated sheet structure (48%) with 20% α-helix, and 32% remaining structure. Human lecithin:cholesterol acyltransferase has a high extinction coefficient at neutral pH. Microsequencing of the amino terminal residues of the enzyme revealed a hydrophobic character. Inactivation of lecithin:cholesterol acyltransferase activity was observed using diisopropylfluorophosphate with a stoichiometry of 1 mole of diisopropylphosphate incorporated per mole of enzyme. This suggests the involvement of a serine residue in the active site of the enzyme, possibly for the formation of an acyl-intermediate. A new quicker assay method for lecithin:cholesterol acyltransferase was developed. This assay involved coupling reaction with acyl CoA synthetase, ΡΡᵢ-dependent phosphofructokinase, aldolase, triosephosphate isomerase and α-glycerol-3-phosphate dehydrogenase monitoring a change in the absorbance or fluorescence intensity due to the oxidation of …

Various modern spectroscopies have been utilized with considerable success in recent years to probe the dynamics of vibrational and reorientational relaxation of molecules in condensed phases. We have studied the temperature dependence of the polarized and depolarized Raman spectra of various modes in the following dihalomethanes: dibromomethane, dichloromethane, dichloromethane-d2, and bromochloromethane. Among other observed trends, we have found the following: Vibrational dephasing times calculated from the bend) and (C-Br stretch) lineshapes are of the same magnitude in CI^B^. The vibrational dephasing time of [C-D(H) stretch] is twice as long in CD2Cl2 as in CH-^C^, and the relaxation time of (C-Cl stretch) is greater in CI^C^ than in CD2CI2. Isotropic relaxation times for all three stretching vibrations are significantly shorter in C^BrCl than in CI^C^ or CI^B^. Application of the Kubo model revealed that derived modulation times are close to equal for equivalent vibrations in the various dihalomethanes. Thus, the more efficient relaxation of the A^ modes in CE^BrCl can be attributed almost entirely to the broader mean squared frequency perturbation of the vibrations in this molecule.

Nuclear magnetic resonance (NMR) provides a convenient probe for the study of molecular reorientation in liquids because nuclear spin-lattice relaxation times are dependent upon the details of molecular motion. The combined application of Raman and Infrared (IR) lineshape analysis can furnish more complete information to characterize the anisotropic rotation of molecules. Presented here are the studies of NMR relaxation times, together with Raman/IR Mneshape analysis of the solvent and temperature dependence of rotational diffusion in 1,3,5-tribromobenzene and 1,3,5-trifluorobenzene. In these experiments, it was found that the rotational diffusion constants calculated from Perrin's stick model were two to three times smaller than the measured values of D, and D,,. Similarly, rotational diffusion constants predicted by the Hu-Zwanzig slip model were too large by a factor of 2. Application of the newer Hynes-Kapral-Weinberg model furnished rotational diffusion constants that were in reasonable agreement with the experimental results. The vibrational peak frequencies and relaxation times of the isotropic Raman spectra of the υ1 modes of CD2Br2 and CHBr3 were studied in solution. The frequency shifts in non-interactive solvents were explained well on the basis of solution variations in the dispersion energy. In Lewis bases, the displacements were in some, but not all, cases …

The synthesis of E- and Z-1,1,2,3-tetramethylsilacyclobutanes is described. Pyrolysis of either isomer at 398.2 °C provides the same products but in different amounts: propene, E- and Z-2-butene, allylethyldimethylsilane, dimethylpropylsilane, the respective geometric isomers, 1,1,2,3,3-pentamethyl-1,3-disilacyclobutane, 1,1, l-ethyldimethyl-2,2,2-vinyldimethyl-disilane and E- and Z-1,1,2,3,3,4-hexamethyl-1,3-disilacyclobutane. Mechanisms involving di- and trimethylsilenes are described for disilane formation and rate constants of the elementary steps for the fragmentation reactions are reported. Photochemically generated dimethylsilylene in the hydrocarbon solution inserts into the cyclic Ge-C or Si-C bonds of 1,1-dimethylgerma- or silacyclobutane to produce 1-germa-2-sila- or 1,2-disilacyclopentane. The relative reactivities of 1,1-dimethylgerma- and silacyclobutanes toward the dimethylsilylene have been determined. The carbenoid resulting from the cuprous chloride catalyzed decomposition of diazomethane at 25 °C in cyclohexane reacts with 1,1-dimethylgermacyclobutane to give, surprisingly 1,1,5,5-tetramethyl-1,5-digermacyclooctane as the major product. The reactions of the carbenoid with 1,1-dimethylsilacyclobutane are described. The kinetics of gas phase thermal decomposition of 1,1-dimethylgermacyclobutane has been studied over the temperature range, 684 - 751 K at pressures near 14 Torr. The Arrhenius parameters for the formation of ethylene are k_1 (s^-1) = 10^(14.6 ± 0.3) exp (62.7 ± 2.9 kcal mol^-1/RT) and those for the formation of propene and cyclopropane are k_2 (s^-1) = 10^(14.0 ± 0.1 ) exp …

The reactions of diagonal and lateral Cp'Re(CO)2Br2 (where Cp' = n5-C5H5, n5-C5Me5) and (n5-CgH7)Re(CO)3 with reducing agents have been examined. Hydride reduction at -78 °C is observed to occur at the Cp ring in both CpRe(CO)2Br2 isomers, affording a thermally unstable [(n4 -C5Hg)Re(CO)2Br2]- complex. The product of hydride ring attack has been characterized by low-temperature IR and 1H NMR measurements in addition to 13C NOE and heteronuclear 2D NMR measurements. Reaction of lateral CpRe(CO)2Br2 with either MeLi or PhLi affords both Cp-ring attack and metalhalogen exchange, [CpRe(CO)2Br]- (1) while t-BuLi reacts exclusively via metal-halogen exchange. diag-CpRe(CO)2Br2 reacts with the above lithium reagents to yield the same metal-halogen exchange anion. Analogous reactions using diag- and lat-Cp*Re(CO)2Br2 (where Cp* = n5-CgMe5) afford only the corresponding rhenium metal-halogen exchange anion, [Cp*Re(CO)2Br] (2). The molecular structures of 1-[Li/15-Crown-5] and 2-PPP were established by X-ray crystallography. 1-[Li/15-Crown-5] crystallizes in the monoclinic space group P21 with a = 10.860(4) A, b = 13.116(5) A, c = 7.417(3) A, B = 105.26(3)0, V = 1018.7(3) A3 , and Z = 2. 2-PPP crystallizes in the orthorhombic space group Pbca with a = 20.646(5) A, b = 17.690(5) A, c = 17.553(3) A, and z = 8. Solution …