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An algorithm is developed that leads to the correct correlation of the vibrational modes of two isotopomers using the concept of a mass reaction path. The mass reaction path is defined by weighted incremental changes of the masses that convert the 'mass reactant' into the 'mass product'.

The study was conducted to investigate the mechanism of the reaction between ethene and 1,-3-butadiene using the unified reaction valley approach (URVA). The results were analyzed by characterizing normal modes, the reaction path vector, and the curvature vector in terms of generalized adiabatic modes associated with internal parameters were used to describe the reaction complex.

A theoretical description of primary kinetic isotope effects for adiabatic proton transfer reaction was presented utilizing a nontraditional picture in which the proton nuclear motion was treated quantum mechanically but was not tunneling. A detarted comparison between the present picture and the standard description was presented.

A thorough evaluation of the estimated power indicates that the gas-phase mechanism of the reaction is governed by radical or biradical mediators, whilst the solution-phase mechanism is distinguished by hydride transfer and the creation of a transitional ion pair which comprises of HOOO- anion. Finally, the amount of ozonation of alcohols and toxicity of ozone consumed in the blood can be determined.

A method has been developed to determine the most stable conformations of puckered rings by a comparison of measured and calculated spin-spin coupling constants (DORCO: determination of ring confirmations). The DORCO method uses the ring puckering coordinates to express the properties of a pseudorotating puckered ring.

The nuclear magnetic resonance (NMR) spectroscopy was used to investigate the (super 13)C, (super 15)N-labeled DNA hairpin molecule of the sequence d(GCGAAGC) = d(G1C2G3A4A5G6C7), and to determine the one-bond and two-bond NMR spin-spin coupling constants. The result shows that one-bond and two-bond coupling constants are very sensitive to the position of the C and N nucleus in the pyrimidine or purine rings.

A research work is presented which determines whether the quantum chemical methods based on single-determinant theory can provide a reliable description of the equilibrium geometry of difluoro peroxide or not. It was found that the molecular dipole moment is a sensitive antenna for probing the quality of the quantum chemical description of FOOF.

Research is done on sixth order Moller-Plesset perturbation theory (MP6) in connection with correlation consistent basis sets cc-pVDZ, cc-pVTZ, and cc-pVQZ that was used to calculate accurate equilibrium geometries for 14 molecules. The experiment reflects the importance of infinite order effects as provided by couple cluster methods some of which are often superior to certain MPn methods.

A study looking into the production of methyl-enecyclopropene from the photochemistry of matrix-isolated butatriene at 10 K is presented.

Issues concerning the r(sub e) structure of cyclopropane are discussed. It was established that reliable results are gained for cyclopropane only if coupled-cluster methods with inclusion of triple excitations are used in combination with large basis sets.

Labile species were isolated after 2,6-dimethylcyclohexa-2,5-dien-1-on-4-ylidene underwent ultraviolet photolysis and matrix isolation in argon at 10 K. The species were found to be alpha,3-Didehydro-5-methyl-6-hydroxybenzene after comparing the results to computations at the ROSS-BLYP/6-31G(d,p) level of theory. Photochemical reactions caused the ring opening of the diradical to produce 3-hydroxy-4-methylhepta-1,2,4-trien-6-yne, thereby indicating Myers cyclo-reversion.

The mechanism of the photodecarboxylation of carbene and the electronic structure of 2,4-didehydrophenol by high level ab initio theory were studied. The thermodynamic role of carbon dioxide formation in the decarboxylation process was emphasized by estimating the heat of formation of triplet carbene. The presence of an intramolecular hydrogen bridge was observed in the x-ray structure analysis of diazo compounds. OH stretching vibrations of free carboxylic acids was also seen by matrix isolation spectroscopy.

Kinetic measurements and B3LYP/ and MP2/6-31G(d,p) calculations show that carbonyl oxides are a significant source of OH radicals when formed i the gas-phase ozonolysis of alkylated alkenes. An investigation into whether carbonyl oxides directly decompose to yield OH radicals was undertaken, using high level ab initio methods. CH200 was found to decompose after H migration and intermediate forming of carbene to OH and formyl radicals. OH radicals were generated during the gas-phase degradation of alkenes by ozonolysis.

Dimesityldioxirane was synthesized via oxidation of dimesitylcarbene. The colorless, cyrstalline dioxirane was entirely stable at -20 deg C and spectroscopic methods, X-ray crystallogaphy and DFT calculations were used to characterize it. Locl C2 symmetry was shown with the mesityl rings twisted by ca. 60 deg. The experimental structural parameters agreed with the theoretical values.

The unexpectedly high stability of the dioxirane CF2O2, its unique geometry, its infrared spectrum and NMR chemical shifts were determined and studied on the basis of extended ab initio computations including seven different techniques and nine different basis sets. Results indicated that the unique electronic structure of the said dioxirane is caused by CF,CF bond interactions which produce a relatively small FCF angle and enhanced pi-donation from the F atoms to the antisymmetric Walsh MO.

NMR/ab initio/IGLO techniques show that silylium cations, R3Si+ and R2HSi+, (R = methyl, ethyl, butyl), form complexes with solvents, (S), in different ratios at varying temperatures. Complex formation depends upon the steric effects of R and S groups, internal stabilization of silyl cation by alkyl group via hyperconjugation, and external stabilization by S-coordination. A tetracoordinate Si is formed with solvents more nucleophilic than methylene chloride in R3Si(S)+ and R2HSi(S)+ complexes. R(sub 3-n)HnSi+, n > or = 1, complex has a pentacoordinate Si and two S molecules.

The stability and structure of trishomocyclopropenylium cations are examined. The magnetic properties and rearrangement possibilities of these cations are also considered. These compounds are investigated with the help of a 6-13G(d) basis set that allows various perturbation levels to be analyzed. Results show that trishomoaromaticity is best indicated by chemical shifts in nuclear magnetic resonance tests and by magnetic susceptability.

The difference between the carbocations and silylium ions is that the carbocations have largely delocalized positive charge due to hyperconjugative and inductive effects, and the interaction with the solvent molecules is weaker compared to that of the silylium ions. The nuclear magnetic resonance chemical shift calculations show that carbocations can exist in solution phases although the carbocation preparation for synthesis of silylium ions in solution is not successful from the stability point of view. The silylium cation can be generated in the solution with proper starting material.

CCSD(T)/6-31 G(d,p) theory, used to analyze the energetics of the Bergman cyclization of enediyne, is more efficient than other techniques and reaction path structures are optimized by this calculation. The absence of biradical character in the transition state reveals the retention of electronic structure. Relative stabilities of o-, m- and p-didehydrobenzene are calculated.

Correlationally corrected ab initio processes are used to examine the potential energy surface (PES) of the C9H9+ ion. The barbaralyl cation reveals 30,240 varying degenerate rearrangements, and each rearrangement is connected to a cycle of six divinylcyclopropylcarbinyl cation rearrangement. The rearrangement process is rapid. A double-bifurcation path connects three first order transition states (TS), revealing the fourfold degenerate rearrangement process.

The binding of the 1, 4-bishomotropylium cation and its organization, steadiness and characteristics are studied. Bicyclic and tricyclic cations exhibit particular chemical characteristics revealed by computationally examining the potential energy surface (PES) of C9H9+. The C9H9+ PES shows a minimum-energy structure which is similar to that of the cation. The homoaromatic (ha) delocalization is likely to be influenced by substituent, counterion or media disturbances.

An ethano-bridged derivative, the tricyclo(4.1.0.0)heptyl cation, of the center-protonated spirocyclopentyl cation is much more stabilized than its parent compound. The pyramidal geometry and the state of coordination of carbon atom C3 are apparently not affected by the ethano-bridge. The ethano-bridge, however, increases the activation energy of a rearrangement to cyclopentyl derivatives.

The reactivity of a natural enediyne dynemicin A is examined, for which the enediyne unit is exchanged by an amidine unit. The implications and the consequences of using dynemicin-amidines (DADs) in finding out the differences between normal and tumor cells and in designing a nontoxic antitumor drugs are described.

A novel method is described for finding a transition state (TS) between a reactant minimum and a quasi-flat, high dissociation plateau on the potential energy surface. The new method is based on the search of a growing string (GS) along reaction pathways that are defined by Newton trajectories (NT).

The QM/MM investigation results of the Bergmann cyclization of the natural enediyne dynemicin A in its triggered form bound to the minor groove of DNA is reported.

The triggering and biological activity of the naturally occurring enediyne dynemicin A, both inside and outside the minor groove of the duplex 10-mer B-DNA sequence d(CTACTACTGG).d(CCAGTAGTAG) is investigated. It is explained why large intercalation energies suppress the biological activity of dynemicin and why double-strand scission can be achieved only in the two-step mechanism that involves two enediyne molecules.

The one-bond NMR spin-spin coupling constant (SSCC) (super 1)J(FH) can be used as a source of information on the electronic structure of the FH molecule. For this purpose, the best possible agreement between measured and calculated SSCC is achieved by large basis set coupled perturbed density functional theory calculations.

It is demonstrated that hemiortho esters (ROH) and acetal hydrotrioxides (ROOOH) are formed in good yields in the low-temperature ozonation of 1,3-dioxolanes and 1,3-dioxanes. The method is an efficient one for the preparation of the hemiortho esters under the investigation.

The NMR spin-spin coupling constant (SSCC) (power 1)J(C-C) is a sensitive antenna for investigating the electronic structure in hyper- and pi-configurated hydrocarbons. The magnetic dipole field of the perturbed nucleus generates orbital currents, which are experienced by the responding nucleus, thus leading to the paramagnetic spin-orbit (PSO) coupling mechanism.

The indirect scalar NMR spin-spin coupling constants across the H-bonds of the protein ubiquitin are investigated. Simple relationships can be set up between the spin-spin coupling constants associated with the H-bond in proteins and the geometrical features of these bonds.

The NMR spin-spin coupling constants (SSCCs) across the H-bond in proteins are sensitive to the electronic structure of the H-bonded system is discussed. In the discussion of the protein ubiquitin, cooperative effects influencing the geometry of HB found and thus also indirectly affect the magnitude of the across-HB SSCCs.

Four different methods and various basis sets ranging from double to quadruple X1 quality are used to calculate the (super 17)O NMR chemical shift values of polyoxides HOnH, CH3OnH, and CH3OnCH3 (n=2,3,4). Averaging of NMR chemical shifts due to the rotational flexibility of the polyoxides has little influence on the measured (super 17)O NMR chemical shifts.

The ozonation of 1,2-diphenylhydrazine and 1,2-dimethylhydrazine is examined. The abstraction of a methyl H atom of the Ch3NNHCh3 radical by HOOO in the solvent cage results in the formation of formic acid and nitromethane in the ozonolysis of 1,2-dimethylhydrazine.

The fermi contact spin density contribution to the isotropic scalar spin-spin coupling constants is studied. It is demonstrated that irregularities in the trends of the measured spin-spin coupling constants (SSCC) can be explained as a simple result of electronegativity and polarizability of the central atom X.

m-Benzyne is generated in low-temperature matrices and IR spectroscopically characterized from four different precursors, for which the perdeuterated derivative 2-d(sub 4) is investigated. While benzyne is stable under the conditions of matrix isolation at low temperature, flash vacuum pyrolysis at high temperature or UV irradiation results in the rearrangement to cis-enediyne.

H atom (HO(sub 3)(super -)) formation by using dioxolanes as suitable model systems that support hydride abstraction by ozone due to the fact that generation of a dioxolyl cation is electronically supported, is studied. The low-temperature ozonation of 2-methyl-1,3-dioxolane in an acetone-d(sub 6), methyl acetate, and tert-butyl methyl ether produced both the corresponding acetal hydrotrioxide ROOOH and the hemiortho ester in molar ratio 1:5 (-78 degree C) is reported.

The HOOO(super -) anion, which can adopt a triplet state (T-1) or a singlet state (S-1), where the former was 9.8 kcal/mol (delta H(298) = 10.3 kcal/mol), which was more stable than the later is reported. The modes of generating S-1 in aqueous solution was discussed, which shows that S-1 represents an important intermediate in ozonation reactions.

Research into the development of seven criteria that lead to a new enediyne anticancer drug being designed. The drug has high activity and selectivity when attacking the DNA of tumor cells, but has low toxicity.

A new study uses CCSD(T), CASPT2 and B3LYP-DFT to investigate the ozonolysis of acetylene.

Spectroscopic characterization, conformation and reaction modes of dimesitylketone O-oxide were studied.

Research is presented describing the techniques used to ascertain the bonding levels of (N,N-dimethylanminoxy)trifuorosilane solutions in all forms using molecular geometry.

Research is presented illustrating the use of unrestricted and restricted DFT calculations to ascertain a precise description of the Bergman Reaction.

The reactions of dimethyl ether with atomic oxygen produced by photolysis of ozone or N2O are investigated in low-temperature matrices. Two conformers of methoxymethanol arise as the major reaction products, and the mechanism of formation of methoxymethanol is examined using UMP, UCCSD(T) and UDFT. The O((super 1)D) insertion and H abstraction reaction shows that the out-of-plane C-H bonds are preferentially attacked due to the greater strength of the in-plane C-H bonds.