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A series of the theoretical calculations are conducted to present a new somersault mechanism for the oxidation step in enzymatic cytochrome P450 hydroxylation of saturated hydrocarbons with the help of a new class of transient inverted metastable metal hydroperoxides. These hydroperoxides involve the rearrangement of the ground-state metal hydroperoxide to its inverted isomeric form and are supposed to have higher energy levels than the ground state compounds.

A theoretical study that addresses the question of whether nucleophilic addition to the carbonyl groups of acid chlorides, esters, and anhydrides involves an addition elimination pathway or proceeds by a concerted S(sub N)2-like mechanism in the absence of the generally assumed tetrahedral intermediate is presented.

The mechanism of 4a-hydroperoxyflavin oxidation of a series of heteroatom nucleophiles is studied using density functional calculations at the B3LYP/6-31+G(d,p) level. Findings provide an estimate of 40kcal/mol for the O-O bond energy in 4a-flavinhydroperoxide (FIHOOH).

High-level ab initio and CASSCF calculations on the transition structure for the peroxyformic acid epoxidation of ethylene is carried out. The objective choice of the active space is demonstrated to be critical to the transition structure obtained.

A comparative study is conducted of the evaluated gas-phase activation barricade for the epoxidation of ethylene with dimethyldioxirane (DMDO) and peroxyformic acid (PFA) and E-2-butene indicates identical oxygen atom contributor capacities for both oxidants. The results show that the epoxidation barricades are slightly larger for the damaged alkenes cyclopropene and cyclobutene than for cyclopentene, indicating the reality that the pressure of strain in the transition stage has not reduced substantially.

Research has been conducted on the dimethyl sulfide oxidation. The use of theoretical calculations in investigating this oxidation is described.

Research has been conducted on the dioxirane dimethyldioxirane. The strain energies of these dioxiranes have been investigated via the use of the high-level computational schemes and the dioxirane reactivity towards alkenes has been predicted.

Research has been conducted on the cyclic molecules' strain energy. The effect of substituents on this energy has been examined and the results are presented.

Research describing processes of nucleophilic substitution in vinylic carbon is presented. Particular attention is given to computational studies of unactivated vinyl substrates, including vinyl chloride in the gas phase as well as complexations of vinyl chlorides.

Quantitative theoretical evidence suggests that the neighboring silicon group is silyl peroxides effectively stabilizes the developing negative charge on oxygen in a concerted transfer of an oxygen atom to nucleophiles. The bond dissociation energy of a dialkyl peroxide is 11-12 kcal/mol less than that of the corresponding silyl peroxide.

Research reveals that the diastereoselectivity in the epoxidation of chiral allylic alcohols is dictated by a hydrogen-bonding between the peroxy acids and the allylic alcohols. Computational analysis of the structural implications of the findings are presented.

The mechanistic features of the oxidation of saturated hydrocarbons with oxidants such as dimethyldioxirane (DMDO) and methyl(trifluromethyl)dioxirane (TFDO) are known, but the transition structure for the insertion reaction is still debated. A computational study provided a strategy for the formation of products derived from free radial intermediates without dioxygen. It supports the concerted oxygen insertion mechanism for oxidation of alkanes with dioxiranes.

A study was conducted on epoxidations of ethylene, propene and isobutene to examine how they are affected by methyl substituents. Results show that the alkene epoxidations proceeded in a concerted way via slightly unsymmetrical transition structures where the differences of carbon-oxygen bond distances at the QCISD/631G level are only 0.021 and 0.044 A. The epoxidation of 1.3-butadiene in a more polarized nature of the double-carbons of alpha,beta-unsaturated systems resulted in an unsymmetrical transition structure where the carbon-oxygen bond distances of 0.305 A at the same level.

Enthalpies and free energies were calculated for different monomolecular dissociations of sulfur mustard using G2(MP2) theory. The results indicate that it may not be viable for this chemical warfare agent to undergo noncatalytic thermal destruction at temperatures up to at least 1800 K. More appropriate high-temperature decomposition pathways involve C-C an C-S bond cleavages. Operating conditions exceeding 2000 K appear to be a requirement for environmentally robust decomposition/destruction.

A computational study was conducted on the oxidation of ethylene, propene, dimethyl sulfide, trimethylamine and trimethylphosphine with peroxynitrous acid. The findings indicate that the three peroxides have different O-O bond dissociation energies but similar activation barriers for oxygen atom transfer. Thus, the correlation of the barrier heights with the O-O bond dissociation energies in the oxidants may not exist at all.

A study was conducted on a mechanism for epoxidation of allyl alcohols where a strong hydrogen bonding interaction dominates the initial reaction trajectory forming a prereaction complex. The findings indicate that an intricate hydrogen bonding network involving both the peroxyacid and the alcohol hydrogens causes the directing effect in the epoxidation of allyl alcohols. Moreover, the hydrogen bonding interaction with the carbonyl oxigen is more important than the trajectory of the approaching electrophilic oxygen atom to the carbon-carbon double bond.

The modeling of the active site of histidine decarboxylase (HDC) with ab initio (MP2/6-31G(d)) and DFT (BH&HLYP/6-311G(d,p)) calculations, illustrates the role of zwitterionic transition structures and the significance of hydrogen bonding interactions in enzymatic decarboxylation. The gas-phase decarboxylation of aminoformylacetic acid and the corresponding process in solution are compared, and the role of proton distribution in lowering the reaction barrier in an intermediated Schiff base is analyzed.

The effect of trifluoroacetic acid catalyst in the rate of epoxidation of (Z)-cyclooctene with m-chloroperbenzoic acid was determined through utilization of kinetic and theoretical studies. Data indicated that the increase in the rate was due to complexation of the peroxy acid with the unddissociated acid catalyst (HA) rather than the protonation of the peroxy acid.

The mechanisms that mediate aromatic nucleophilic substitutions during the reaction of halide anions with halobenzenes and halonitrobenzenes were analyzed based on ab initio computations. Ab initio analysis of the identity of the halide-exchange reaction indicated the presence of multistep SNAr reactions that involved the formation of an intermediate sigma-complex. Furthermore, the first stage of the gas phase aromatic nucleophilic substitution reaction induced the formation of a loose ion-molecule prereaction complex.

Ab initio calculations were performed at the G2 and QBS levels of theory to determine the oxygen-oxygen bond dissociation enthalpies for a series of diacyl peroxides at 298 K. The peroxides were HOOH, CH3OOH, CH3OOCH3, HC(O)OOH and CH3C(O)OOH. The results, which show good agreement between G2 and QBS predictions, indicate that the generic bond dissociation energy of 34 kcal/mol. assigned to peroxides should be raised to around 54 kcal/mol. in light of their sensitivity to the bonding environment.

The potential energy surface for front-side attack in gas-phase identity nucleophilic substitution (S(sub N)2) reactions of halide anions with methyl halides with retention of configuration was investigated via ab initio calculations at the G2(+) level. The simulations, which looked at X(sup -) + CH3X where X = F,Cl,Br,I, showed gas-phase barrier heights that are higher than those for back-side S(sub N)2 reactions.

The decarboxylation of beta-keto acids involves a complete proton transfer from the carboxylic acid to the beta-carbonyl group which leads to the formation of a dipolar ion in the transition state. The dipolar intermediate of the beta-keto acid exhibits an increase in the rate of decarboxylation when the dielectric constant of the solvent decreases. The rate of enzymatic decarboxylation is also enhanced by the polarizable sulfur atom and a positively charged ammonium group.

Catalytic extraction processing is an innovative technology for the conversion of potentially hazardous organic, organometallic, inorganic and ash waste streams into useful and marketable commercial products. It has been validated by the EPA as a technology that meets and even surpasses its waste treatment standards. The technology involves the injection of feed materials into a molten metal bath where dissociation of molecular entities to their elements and product formation occur.

A study of the relative reactivity of a series of nucleophiles towards peroxyformic acid, in both condensed and gas phase using ab initio molecular orbital theory finds that protic solvents play a major role in determining the relative reactivity of these nucleophiles. Solvation effects and the exo- versus endothermicity of oxygen transfer from a peroxy acid has much greater influence upon the relative nucleophilicity than polarizability.

The calculated values of kinetic isotope effect of intramolecular elimination reaction are in accordance with the experimentally determined values. The primary and secondary isotope effects can be evaluated by using intramolecular Cope elimination, involving thermal decomposition of an amine oxide. The intramolecular Cope elimination reaction is an intramolecular syn-elimination. The transition state geometries for Cope and ylide reactions can thus be evaluated by the calculations.

A 12-step synthetic sequence enables the preparation of (+ or -) -fredericamycin A with an overall yield of 6%. A two-step 1,4-dipolar cycloaddition helps couple the upper and lower units of (+ or -) -fredericamycin A. A mercury-catalyzed pinacol rearrangement involving 1,2-carbonyl migration helps introduce the spiro-1,3-dione center in fredericamycin. Synthesis of isochromarins involves the reaction of benzylic cuprate anions ortho to aromatic esters and the reaction of ammonia with these isochromarins produces biologically important isoquinolones.

Ab initio calculations help determine the activation barriers for 1,3-hydrogen shift in hydrogen peroxide and hydroperoxonium ion and for the hydroxylation of saturated hydrocarbons with hydroperoxonium ion. A cluster formed between hydroperoxonium ion and isobutane is more stable by 7.15 kcal/mol compared to isolated reactants. Frontier molecular orbital model helps predict the reaction pathway for the approach of H3O(sub 2)(super +) to the hydrocarbon and the transition state structure.

Ab initio molecular orbital methods are employed to analyze hydrogen peroxide oxidation and its oxygen transfer mechanism from the hydroperoxy functional group. An ionic pathway is observed in alkyl hydrogen peroxide oxidation in the absence of acid catalysis, in which rate-limiting oxygen transfer precedes proton transfer. In the presence of water, 1,4-hydrogen shift is followed by oxygen-transfer step.

Ab initio molecular orbital calculations are used to analyze the influence of inductive and Coulombic effects on the oxygen atom transfer in the oxidation reactions of alkyl hydroperoxides with the help of 4alpha-flavin hydroperoxide. Inductive effects have little influence on the barrier heights for the transfer of oxygen atoms. Oxygen donor capacity of flavin hydroperoxide is due to hydrogen bonding, observed in the transition state.

A model based on ab initio molecular orbital calculations was developed to explain the stereochemistry of bicyclo(2. 1.0)pentane hydroxylation. The cyclopropylcarbinyl moiety in bicyclo(2.1. 0)pentane was found to stereoelectrochemically influence the free-radical and electrophilic pathways for hydroxylation. Bicyclo(2.1.0)pent-2-yl radical behaves as an intermediate in P-450 hydroxylation of certain hydrocarbons.

A frontier molecular orbital model explains the process of insertion of singlet divalent carbon (CX2, X = H, double bond CH2,CH3,F) and silicon (SiH2) into saturated hydrocarbons. The model facilitates the prediction of an approximate route, and offers a rationale for the orientation of the carbene lone pair in the transition state, for insertion.

Methyl substituents on N,N-dimethyl-alpha-ketopropanamide reveal steric reactions. N, N-dimethyl-alpha-ketopropanamide moves away from planarity and causes the lack of a syn-conformer as a local minimum due to the interaction. Crystal geometry of FK506 reveals orthogonal orientation which shows a torsional profile and the size of the obstacle for C-C bond rotation. These features are similar in the compound due to the reaction. Easy exchange of the cis and trans structures for the amide bond in FK506 at ambient temperatures is revealed by the size of the C-N rotational obstacle in the compound.

The 3-21 G basis and the Wachters-Hay basis set were used to optimize the equilibrium structures and transition states at the UHF and UMP2 levels to study diamidoiron (III) hydroperoxide as an extremely simplified model for the hydroperoxide intermediate in hemoproteins such as peroxidases and cytochrome P-450. The geometry and bonding could not be appropriately determined without the MP2 level. The development of the ferryl complex could be preceded by oxygen atom transfer from ion hemoproteins in some instances.

A study used water oxide (H2O-O), as a model singlet oxygen atom donor, to propose the mechanistic process for the oxidation of saturated alkanes to their respective alcohols and ketones. Molecular orbital estimations hint that oxygen insertion by water oxide takes place because of the interaction of an electrophilic oxygen atom with a doubly occupied hydrocarbon fragment orbital.

The complexation of mercuric chloride and silver trifluoromethanesulfonate with several alkenes was studied using nuclear magnetic resonance spectroscopic analyses. The results were based on the formation constants calculated from the spectra of the observed complexes. Moreover, the data revealed that the rate-determining step in the bromination reaction was the formation of the bromonium ion while for oxymercuration, the solvent attack on the mercuronium ion was the rate-determining step.

A study was conducted to determine the electronic structure and chemical reactivity of dioxirane, diradical dioxymethane, and carbonyl oxide at various levels, including MP2, MP4, CASSCF and QCISD. Results of the study showed that accurate structures of dioxirane and carbonyl oxide were devised at the MP2 level. The QCISD level, however, did not offer an optimum carbonyl structure. The C-O/O-O bond length ratio for carbonyl oxide was established correctly at both the levels.

The asymmetric oxidation of enolates with N-sulfonyloxaziridines results in the production of highly enantioselective alpha-hydroxy carbonyl compounds. A molecular orbital system serves as a model for the transition state of oxygen atom transfer that takes place in the synthesis. The transition state involves the positioning of lithium cation in the oxygen atoms of both enolate and oxaziridine compounds. The binding of sulfonyl oxygen atom and lithium cation affects stereoselectivity of the resulting alpha-hydroxy carbonyl compound.

A free radical cation chain reaction allows the conversion of quadricyclane (Q) to norbornadiene (N), despite a high thermal barrier for reversion. One-electron oxidations start the chain reactions and the conversion of Q to N releases energy. The electronic structures of the radical cations of Q and N, namely Q(super .+)and N(super .+), are symmetrical. A study predicts a half life of 9.14 X 10 to the -6th power at 298 K for valence isomerization of Q(super .+) to N(super .+).

Quantum mechanical calculations (DFT) have described a mechanism for the oxidative C-H bond cleavage step in Fenton-like hydrocarbon hydroxylation. The transition structure for the oxidation step in anionic iron(III) hydroperoxides has displayed a resemblance to model porphyrin calculations on cytochrome P450 hydroxylation.

Ring strain energies (SEs) and enthalpies of hydrogenation of a series of E- and Z-alkenes, cyclic alkynes and allenes are computed at the G3 level of theory. The activation energies for [3+2] cycloaddition to benzyl azide and acetamido azide to DIFO are lower in energy than cycloaddition to cyclooctyne.