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The nematic and twisted nematic liquid crystals mixed with azobenzene (AB), spirooxazine (SO) and spiropyran (SP) are investigated by using spectroscopic methods, including birefringence and polarized transmission, to monitor the amplitude of the changes upon phototransformation as well as the dark kinetics. The results have shown SP to be an interesting photochemical probe as it has orientation photochromism and is able to adequately sense the orientation dependent polarity of this anisotropic medium.

The investigation focuses on the formulation of semiempirical method, to predict and represent inter-molecular interaction in [M.sup.+]- benzene systems, and on a critical analysis of its results, conducted by performing extensive ab initio calculations at defined geometries of the systems. The agreement between potential energy scans semiempirically obtained and ab initio results is good for all the investigated geometries, thus showing that the adopted representation is in general able to reproduce all the main features of the potential energy surface for these systems.

The reaction enthalpy (298 K), barrier (0 K), and activation energy and preexponential factor (600-800 K) is examined computationally for the abstraction of hydrogen from benzene by the methyl radical, to assess their sensitivity to the applied level of theory. Inspection of the theoretically calculated rate parameters reveals a minor dependence on the level of theory for the preexponential factor.

The mechanism of a new class of reactions, the associative charge transfer (ACT) reaction that is activated by partial charge transfer to the polymerizable ligand in the [benzene.sup.>](propene) dimer, is examined. The ACT reactions of ionized benzene and PAHs are found to catalyze the formation of complex interstellar molecules.

The kinetic energy release distributions (KERDs) associated with the hydrogen loss from the benzene cation and the deuterium loss from the perdeuteriobenzene cation are remeasured on the metastable time scale and analyzed by the maximum entropy method. The results show that the larger the energy stored in the transitional modes, which partly convert to the relative interfragment motion, the shorter the value of the reaction coordinate at which the adiabatic channels cross, and larger the probability of undergoing the [super 2]A[sub 2]->[super 2]A[sub 1] transition required for hydrogen loss.

The collisional energy transfer (CET) in self-collisions of benzene, toluene, p-xylene and azulene is reported. The mechanisms of CET are short, impulsive collisions and long-lived chattering collision where energy is transferred in a sequence of short internal encounters during the lifetime of the collision complex. The dynamical effects are shown to control CET.

The potential of tetrazolate-based ligands for forming metal-organic frameworks of utility in hydrogen storage is demonstrated with the use of 1,4-benzeneditetrazolate (BDT.sup.2-) to generate a series of robust, microporous materials. It is shown that the method for desolvating such compounds could dramatically influence the ensuing gas sorption properties.

Density functional theory is applied to gain insights into the regioselectivity of nucleophilic attack and protonation of electron-deficient benzoheterocycle triosmium clusters. Computational studies are conducted of the reaction of the green 46-electron triosmium clusters [Os.sub.3][Co.sub.9]{[mu.sub.3].[eta.sup.2]-(LH)}(mu-H) to understand factors affecting the observed differences in the structure of the kinetic products.

Pump-pump-probe spectroscopy is used to investigate the ultrafast ground state recovery (GSR) dynamics of the radical cation of perylene, [Pe.sup..+], which is generated upon bimolecular photoinduced electron transfer in acetonitrile. The change of dynamics observed with 1,4-dicyanobenzene is attributed to the transition from paired to free solvated ion.

The solvation of c-[C.sub.3][H.sub.3][.sup.+] ions and their deprotonation by water through associative proton transfer (APT) reactions are studied. The behavior of the [C.sub.3][H.sub.3][.sup.+]/water system is the same as the [benzene.sup.-*]/water system indicating that the mechanism, kinetics and large negative temperature coefficients may be general to multibody APT reactions.

A concise alternative approach is reported for the synthesis of a range of aryl-substituted cyclohexenediols and cyclohexanetetraols involving the reductive radical arylation of benzene and subsequent treatment with osmium tetroxide. The method is conceptually related to the work of Landais on the desymmetrization of cyclohexadienysilanes generated by Birch reduction or arylsilanes.

The two-dimensional supramolecular host structures are realized by adsorption of benzenetribenzoic acid (BTB) molecules on graphite surfaces from the liquid-solid interface. The scanning tunneling microscopy (STM) has shown that the low conformational flexibility of BTB is supportive to combat the tendency for dense packing.

A study was conducted on thermal decomposition of the benzyl radical in shock tube experiments using ultraviolet laser absorption for detection of benzyl. Benzyl iodide was used as a benzyl precursor, providing instantaneous yields of benzyl following reflected shock heating.

The title compound was synthesized to produce stacked benzene-like [Sn.sub.6.sup.6-] rings separated by alkaline-earth cations in analogy with reported stacks of aromatic cyclopentadienyl-like [Sn.sub.5.sup.6-] in [Na.sub.8-]Ba[Sn.sub.6]. The resulting compound has the correct stoichiometry with six tin atoms and six positive charges.

An efficient approach toward novel 2-(cyanomethyl)-aziridines with high synthetic potential is described in a one-step procedure starting from 1-arylmethyl-2-(bromomethyl)-aziridines. Methyl N-(2-chloro-1-(cyanomethyl)ethyl)benzimidates proved to be excellent substrates for the 1,3-intramolecular ring closure by means of KOtBu in THF toward biologically important N-(2-cyanocyclopropyl)benzimidates as [beta]-aminocyclopropanecarboxylates precursors.

High level ab initio quantum chemical calculations are conducted on the binding of alkali metal to benzene with special attention to heavier metals. BSSE-corrected geometry optimizations are performed employing the MP2 level of theory with large basis sets and a modified Stuttgart RSC 1997 basis set for rubidium and cesium.

The synthesis and two photon-induced absorption (TPA) properties of a functionalized distyrylbenzene (DSB) containing a tetra-azacyclododecane (cyclen) receptor for Zn(II) are presented. The experiments show that the TPA action spectrum of uncomplexed distrylbenzene, at 750 nm employing nanosecond-long excitation pulses, is 5 times more intense than that of the complexed form.

The 2PA absorption spectrum of a family of perylene tetracarboxylic derivatives (PTCDs) is investigated. These PTCD compounds exhibit extremely large two-photon absorption (2PA) cross-sections in a wide spectral region, which make them strong candidates for photonics applications involving 2PA.

The interaction of the highly cross-reactive anti-PAH monoclonal antibody with four diastereomeric benzo[a]pyrene tetrols (BPTs) is studied by means of fluorescence line-narrowing spectroscopy. It is shown that the interaction of enantiomers of cis-BPT and trans-BTP with the antibody involves different complex geometries.

Various N-F reagents reacted with hexamethylbenzene forming side chain substituted alkoxides or esters in protic solvents. Ritter type side chain functionalization is observed in acetonitrile in the presence of trifluoroacetic acid, while in aqueous acetonitrile solution phenyl ring transformation took place, starting with ipso attack of water and further rearrangement of the methyl group as the main process.

The cobalt-containing product sample in neat benzene is analyzed by both electron paramagnetic resonance (EPR) and Fourier transform infrared spectroscopy and the magnetic parameters (g tensor and Co hyperfine interaction) are determined for the Co(C6H6)(sub 2) sandwich compound. A bonding scheme that is consistent with both the EPR and IR data for Co(C6H6)(sub 2) is discussed.

RNA-based stable isotope probing (RNA-SIP) technique is used to label and identify anaerobic benzene-degrading organisms from gasoline-contaminated aquifer. The results have revealed that the Azoarcus population is involved in the benzene degradation in the gasoline-contaminated groundwater under denitrifying conditions.

Mono- and bis-oxadisilole-fused isobenzofurans are first synthesized and isolated and then a series of mono-, bis-, and tris-oxadisilole-substituted acenes are synthesized by benzyne Diels-Alder reactions with the isobenzofurans. The photophysical, redox, and thermal properties of these new acenes are characterized.

A systematic study was performed about the solvolysis reaction of substituted benzoyl chlorides in the presence of zwitterionic vesicles of dipalmitoyl phosphatidylcholine (DPPC). For benzoyl chlorides with electron-donating groups, which react predominantly through a dissociative mechanism, which is strongly affected by medium properties, the rate constant decreases as the vesicle concentration increases.

The rate constants for the reactions of OH radicals with benzene and toluene are measured directly by a shock tube/ pulsed laser-induced fluorescence imaging method at high temperatures. The direct measurements of the high-temperature rate constants for the reactions of OH radicals with benzene and toluene is extended up to 1740 and 1480 K, respectively, and are in good agreement with the previous measurements.

A study have synthesized the new dendritic oligoarylamine by using the successive palladium-catalyzed amination reactions in order to improve the stability of the highly charged species of 1,3,5-triaminobenzene, which are one of the interesting and fundamental organic high-spin molecules. Conclusion suggests that the molecular structure is deformed in the solid state to have different exchange coupling constants among three spin centers.

The transitions in a series of prototypical complexes in depth were studied in combination of resonance Raman spectroscopy and quantum chemistry. These studies have defined the information content of absorption and rR spectroscopy for the compounds investigated and such transitions occur when the ligands have significant open-shell character.

The growth of long carbon fibers was investigated using hyperbaric-pressure laser chemical vapor deposition (HP-LCVD). The growth rate was directly proportional to the square root of the precursor molecular weight for the alkenes, and while the alkynes exhibited an inverse relationship, the reaction order for the alkenes was 1.65, and for benzene was 2.25 and the volumetric rate increased nonlinearly with laser power at sufficiently high pressures.

Solid-supported acids are investigated for aromatic debenzylation reactions. Stoichiometric amounts of solid-supports acids in refluxing toluene with or without 4 equiv of methanol effectively provided the desired aromatic debenzylation products of various systems in moderate to excellent yields (up to 98%).

The results on the experimental and computational studies of the hydrogen-bond-promoted enantioselective hetero-Diels-Alder reaction of Danishefsky's diene with benzaldehyde are reported. The results indicate that carbonyl group of benzaldehyde is activated by forming an intermolecular hydrogen bond with one of the hydroxyl groups of the alpha,alpha,alpha',alpha'-tetraaryl-1,3-dioxolane-4,5-dimethanol molecule.

The outcome of reactions of 1-bromo-4-tert-butylbenzene, a representative aryl bromide, with n-BuLi or t-BuLi at 0 degree Celsius in a variety of solvent systems is investigated. The products of reactions of 1-bromo-4-tert-butylbenzene with n-BuLi vary significantly with changes in solvent composition.

A quantitative study of the variation of the conformational equilibria of 7-benzyl-2-iodo-9-oxa-7-azavbicyclo[4.3.0]nonan-8-one in 10 solvents is conducted. Analysis of the conformational populations in different solvents enabled the establishment of mathematical correlations between the equilibrium composition andd empirical solvent parameters.

The second hyperpolarizabilities of bisimidazole- and bistriazole-benzene compounds are calculated at different levels of approximation to unravel the effects of diradical character as well as of charge and spin multiplicity. A discussion is presented on the diradical character and the spin state control of third-order nonlinear optical properties of diradical molecular systems.

An investigation is conducted of the relative importance of hydrogen bonding versus pie stacking interactions in DNA where the hydrogen-bonded complexes of the nucleobase mimic 2-pyridone (2PY) with seven different fluorinated benzenes. Ab initio studies are performed on the individual hydrogen bonds occurring between nucleobases and fluronated isomers.

A study conducted on modified DNA oligomers and polymerase reactions have demonstrated that canonical nucleobases can exhibit stable and even selective pairing with shape-complementary fluorobenzene nucleotides. Hydrogen bonds are believed to be absent because of the fluorination of the pairing edges and the local DNA stability is attributed pie-stacking and shape complementarity.

Raman spectroscopy was used to examine the interactions of the free O-H bonds in n-octanol and ethanol with the organic solvents carbon tetrachloride [CCI(sub 4)], cyclohexane, and benzene. These spectra reveal that the solvents CCI(sub 4) and cyclohexane have a small effect on the free O-H peak of alcohols, whereas benzene as a solvent significantly red shifts the free O-H band.

1,2,4,5-Hexatetraene (1245HT) is synthesized and pyrolysized in a single-pulse shock tube at two nominal pressures of 22 and 40 bar over a temperature range of 540-1180 K to determine if it is indeed an intermediate to benzene formation. The analysis indicates that, at low temperatures, there is an apparent isomerization between 1,2-hexadien-5-yne (12HD5Y) and 3,4-dimethylenecyclobutene that predominantly removes 12HD5Y.

The Car-Parrinello molecular dynamics (CPMD) method is used to study the dynamic characteristics of the cation-pi interaction between ammonium and benzene in gaseous and aqueous media. This method has provided strong evidence that cation-pi interactions might take place even on the surface of proteins or nucleic acids in an aqueous environment.

Fresh DNA derivatives are synthesized having halogenated recognition bases or benzene rings and the effects of the modifications on the triplex stability as well as selectivity are evaluated. It is reported that the triplex-forming oligonucleotides (TFO) containing WNA-betaT and WNA-betaC stabilizes a TA or a CG interrupting site, respectively with high selectivity and stability.

The carbon 1s ionization energies for all of the carbon atoms in benzene molecules are measured by high-resolution photoelectron spectroscopy. A comparison of the ionization energies and proton affinities gives insight into the effects of fluorine as an electron-withdrawing group and as a pi donor, both in the neutral molecular and in response to an added positive charge.

(super 1)H NMR spectra of p-xylylene, alpha-methyl-p-xylylene and 2,6-dimethyl-p-xylylene are observed at room temperature and this allows a more detailed study of their chemistry. The absence of acyclic dimer, the analogues of which were present in the product mixtures of the alpha-methyl thiophene-based p-Quinodimethanes (p-QDM) and the alpha-methyl furan-based o-QDM are explained by the conformational limitations of the dimeric diradicals of the benzene-based p-QDMs.

The low-temperature protonation chemistry of (N-N)PtPh2 complexes, where a choice between Pt(II) and Pt(IV) products is available depending on the reaction conditions is described. In the absence of strongly bonded ligands, Pt(II) phenyl/pi-benzene complexes (N-N)Pt(C6H5)-(eta(super 2)-C6H6)(super +) are formed.

A study investigates the electronic and magnetic properties of the proposed one-dimensional transition metal, benzene sandwich polymers by means of density functional calculations. Results indicate that the 1D organometallic sandwich polymers are possible candidates for spintronic devices for spin-polarized transport since the polymers with an inherently uniform size are supposed to be also ferromagnetic (FM).

Salts of the C(sub 3nu) symmetric hydronium ion, H3O(super +), are obtained in the weakly basic solvents benzene, dichloromethane and 1,2-dichloroethane. This is made possible by using carborane counterions, since they combine the three required properties of very low basicity, low polarizability and high chemical stability, of a suitable counterion.

The ARS-E model was used for calculating the intermolecular interaction energy of hexafluorobenzene-benzene. The largest and most negative energy of -5.38 kcal/mol was observed in the slipped-parallel complex.

A pulsed Laval nozzle apparatus is used for examining the reaction of the C2H radical with benzene at low temperature. Rate coefficients over a temperature range between 105 and 298 K are observed.

The formation of the benzyl-type radical in the of 1,2,4-trimethylbenzene is discussed. The 3,4-dimethylbenzene is the most dominant product of the corona discharge which is formed by the extraction of a hydrogen atom from the methyl group at the 4-position.

Two fluorine-containing bix (Fbix) ligands 2,3,5,6-tetrafluoro-1,4-bis(imidazol-1-yl-methyl)benzene and 2,3,5,6-tetrafluoro-1,4-bis(2-methylimidazol-1-yl-methyl)benzene were reported. The resultant non-interpenetration polymeric complexes formed by coordination of these ligands with metal salts, AgNO3, Co(ClO4)2.6H2O, Cd(NO3)2.4H2O, are reported as well as their solid-state structures.

A number of functional 3D networks based on the coordination bonds between the silver(I) ion and polycyclic aromatic 2,3,6,7,10,11-hexakis(organylthio)triphynelene (HRTT) molecules are described. First, 2,3,6,7,10,11-hexakis(phenylthio)triphynelene (HPhTT) chelates with AgBF(sub 4) in the presence of hexafluorobenzene to form a 3D network with 8(super 2) 10-a topology and second, chelation of 2,3,6,7,10,11-hexakis(4-methoxyphenylthio)triphynelene (HMOPhTT) and AgSbF9sub 6) results in a 3D network featuring similar topology and Ag(I) coordiantion.