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Benzene, toluene and binary mixtures of these molecules in the gas phase are studied using femtosecond time-resolved anti-Stokes Raman scattering (CARS). Results show that the CARS signal indicates no oscillatory patterns and decays for benzene while temporal variations reflecting the vibrational periods of the system are observed for toluene. For benzene and toluene mixtures, a strong oscillation in the transient signal corresponding to a beat between the vibrational mode in the benzene and toluene is found.

A study was conducted to describe a model system for very large third-order optical polarizabilities for microscopic systems that characterizes high dimensionality delocalization as a series of stacked benzene rings. System computations were carried out either as single neutral or single dications using Semichem Inc's AMPAC 5.0 software. In addition, calculations on the charged systems were determined during the absence of counterions.

The 'capped' azobenzene derivative, trans 1, in which large-scale motion of the phenyl groups was inhibited by their connection to a bridging azacrown ether was investigated through the utilization of the ultrafast time-resolved ultraviolet (UV)-visible absorption spectroscopy. It was observed that the transient absorption dynamics on UV excitation of trans-1 were different from those on UV excitation of trans-azobenzene. The rotational freedom limitation of the phenyl groups affected both the ultrafast dynamics and the photoisomerization process.

A new category of porphyrin array was synthesized through the coupling of six porphyrin moieties to a central benzene core via an ether linkage. The porphyrin supermolecule product has a diameter up to 80 angstroms and a mass of 8.5 kD. In solution, the six porphyrins surrounding the central benzene ring arrange themselves into three groups of offset overlapping dimers, which are rapidly interconverting at room temperature.

A study was conducted to investigate the thermolysis of the benzene anion radical 18-crown-6 complex. Anion radical salts were produced under a high-vacuum environment by minimizing neutral benzene on a distilled potassium mirror. Results indicated that the addition of electrons to polyaromatic hydrocarbons supported thermal C-C and C-H bond activation. Findings also showed that hydrogen was lost during the polymerization of the anion radical.

The synthesis of star-shaped poly(1,2-phenylenevinylene)s 4-substituted with high-spin polyphenoxyls via polymerization of 2-bromo-4-(acetoxyphenyl)styrene in the presence of 1,3,5-triiodobenzene or 1,3,5-tris(3',5'-diiodophenyl)benzene as the core was described. A simple one-pot Heck reaction and subsequent hydrolysis, phenolate formation and heterogeneous oxidation were employed in the experiment. Results showed that the 1,3,5-benzene core is an effective magnetic coupler in aligning the spins of the multiple pendant phenoxyls through the star-shaped backbone.

The interaction with the pi electron systems of aromatic side chain residues is believed to stabilize carbocation intermediates in enzymatic reactions. A computational study of the delta complex and areas of the energy surface corresponding to three types of pi complex of methyl cation with benzene, has been undertaken. The results support the premise of fundamental differences of the carbocation-pi interaction from the pi interaction of coordinatively saturated cations.

Research was conducted to examine the dual fluorescence and multiple charge transfer nature in N-Pyrrolobenzonitrile, its ester derivative PBAEE and the model compound DPBN. Special features can be expected and large charge separation is even possible for planar geometries due to the particular electronic characteristics of pyrrol with a node-through N in the highest molecular orbital. Results indicate emission from an equilibrium involving a charge transfer state with an unstructured spectrum and a less polar locally excited state with structured emission.

Research was conducted to examine the electronic absorption spectrum of the hexamethyl(Dewar benzene) radical cation. Samples were prepared by immersing room-temperature solutions in liquid nitrogen. Photochemical reactions were performed with a 450 W xenon arc lamp as a light source. Results based on the distribution of reaction rates clearly suggest that the activation barrier for the process is strongly influenced by environmental factors.

A study examined the kinetics and mechanism of solvent turning in supercritical fluids (SCFs) and demonstrated solvent tuning in these fluids. Findings revealed the multiple effect of push-pull azobenzenes in pure SCFs on the rate of thermal isomerization. A correlation was found between the variation in rate constant with density and the density of the solvent for pure SCF ethane and carbon dioxide. The confluence of local composition enhancements and specific interactions was found to result in substantial increase in reaction rate.

Nuclear magnetic resonance and kinetic and thermodynamic approaches were used to examine the ionization of a series of benzyltriflones which resulted in conjugate carbanions in Me2SO and some H2O-Me2SO mixtures. Results favored the idea that charge polarization effects are the most important mechanism contributing to the stabilization of conjugate carbanions. These also showed a structural picture of the triflone carbanions in solution which did not fit with data based on solid-state or computed gas-phase studies.

The dynamics of dissociation of n-propylbenzene molecular ion were investigated using mass-analyzed ion kinetic energy spectrometry. Specifically, the production of C(sub 7)H(sub 7)(super +) from the ion was examined and the kinetic energy release distributions in photodissociation and metastable ion decomposition were calculated. Experimental results revealed the C(sub 2)H(sub 5)(super *) loss of the n-propylbenzene molecular ion.

The mechanism of photodissociation of the bromobenzene molecular ion was investigated on a nanosecond time scale using photodissociation mass-analyzed ion kinetic energy spectrometry. In addition, the rate constant and kinetic energy release distribution were examined. Experimental results showed that the rate-energy data available over six orders of magnitude in time scale could be fit with a nontotally loose transition state model proposed by Rosenstock and colleagues. The model, however, predicts rate constant values larger than theoretically acceptable at high internal energy. An alternative model based on a completely loose transition state was suggested.

Thermal and visible light-induced reaction of benzene-Cl2 gas mixtures loaded into zeolite NaZSM-5 was investigated. Results show that 1,4-dichlorobenzene is formed as the sole dichloro product when loading the reactant gas mixture into zeolite NaZSM-5 at -100 degrees C, a selectivity that is unprecedented. No other products aside from chlorinated benzenes are observed even at elevated temperatures or high conversion. Irradiation of 1,4-dichlorobenzene with green or blue light yielded 1,2,4-trichlorobenzene as the only product at high conversion.

Ab initio quantum mechanical calculations were used to investigate proton-catalyzed bimolecular reaction of isopropylbenzene with benzene leading to n-propylbenzene. According to computations on the fully relaxed complex of protonated isopropylbenzene and benzene, n-propylbenzene formation cannot be expected on catalysts with nonrestricted reaction space. A constrained model confirmed the existence of a reaction pathway leading to n-propylbenzene formation, affirming experimental data.

The carbon-13 chemical shielding tensor in the liquid state of hexafluorobenzene which has a complicated spin system may be determined using simple experimental nuclear magnetic resonance methods combined with quantum chemistry calculations. Modifications of the electronic distribution around the carbon nuclei in hexafluorobenzene when going from pure solid to pure liquid or solutions were attributed to the particular arrangement in the solid phase.

A study was conducted to analyze the cyclotrimerization of acetylene to benzene on a Pd(111) surface by scanning tunneling microscopy. An ultrahigh-vacuum chamber was utilized to perform the experiment. The Pd(111) sample was cleaned by circles of argon ion sputtering at room temperature. Results indicated cyclotrimerization reaction at 140 K in disordered areas. Findings also showed that the cyclotrimerization of acetylene to benzene correlated with a transient state of acetylene.

A study was conducted to analyze the structural transformations of the C70 in benzene, toluene, and hexane solutions using x-ray powder diffraction techniques. The crystals were prepared from a benzene solution by slow evaporation. The Siemens D5000 diffractometer was utilized to carry out the x-ray diffraction experiments. Results indicated an orthorhombic structure for low-temperature phase and a mixture of a monoclinic phase supporting pure hcpI phase for high temperature.

A study was conducted to analyze C-H and C-NO2 dissociation energies in some azines and nitroazines. A density functional process was utilized to carry out the analysis. The C-H and C-NO2 dissociation energies were computed and given in decreasing order. Experimental results indicated that variations within two isomeric groups can be correlated with the relative stabilities of the product radicals.

A study was conducted to analyze the dipole moments of exciplexes determined between the electronically excited electron acceptors 9,10-dicyanoanthracene or 2,6,9,10-tetracyanoanthracene and methyl-substituted benzene donors. A transient de photocurrent method was utilized to carry out the analysis. Experimental results indicated that increases in the dipole moment correlated with decreases in donor oxidation potential and saturates.

A study was conducted to characterize the crystal structure of a benzene sorption complex of dehydrated fully Ca2+-exchanged zeolite x. The cubic space group Fd3 was utilized in the x-ray data collection. Full-matrix least-squares refinement was started at the atomic parameters of the framework atoms. Experimental results indicated that the maximum number of benzene molecules that can occupy each Na-Y supercage is between 4.9 and 5.2

1-(Alkylamino)-3,5-dichloro-2,4,6-trinitrobenzenes were synthesized through aromatic substitution reactions that involve sym trichlorotrinitrobenzene and amines. The yields and relative formation were found to be a function of the degree of alkylation of the nucleophile. For ammonia and monoalkylamines, the introduction of a second and third donor was supported. The findings were attributed to the intramolecular hydrogen bonding as verified by X-ray analysis of 3,5-dichloro-2,4,6-trinitroaniline.

1,3-Bis(2-cyano-2-alpha-thienylethenyl)benzene, 1,4-bis(2-cyano-2-alpha-thienylethenyl)benzene and 2,7-bis(2-cyano-2-alpha-thienylethenyl)benzene were synthesized by electrogenerating polymeric thin films on electrode surfaces. The second compound can be reversibly reduced to produce the corresponding dianion, while the reduction of the other two compounds were either quasireversible or reversible. The diradicaloid properties were proposed to account for the high reactivity of the dianions of the two compounds.

3,4-Di-tert-butyl-, 3,4-dineopentyl, 3,4-di(1-adamantyl)- and 3-(1-adamantyl)-4-tert-butylthiophenes were synthesized in high yields via intramolecular reductive coupling of 3-thiapentane-1,5-diones and acid-catalyzed dehydration of thiolane-3,4-diols. The oxidation of the synthesized compounds with m-chloroperoxybenzoic acid resulted in thiophene 1,1-dioxides. The Diels-Alder reaction of the latter with phenyl vinyl sulphone yielded o-dineopentyl-, o-di(1-adamantyl)-, o-di-tert-butyl- and o-(1-adamantyl)-tert-butylbenzenes.

A new electrostatic method for the analysis of the electronic perturbations due to the substituents attached to benzenes is proposed. The approach consists of the most negative-valued molecular electrostatic potential minimum observed over the benzene ring. Five different substituents with widely differing electronic effects were used in the study. The simultaneous effect of any two substituents, arranged in para, meta and ortho orientations over the aromatic pi-electron distribution is explored.

Pathway C among three different attackss of (super 3)sigma(sub g) O2 on the hydroxycyclohexadienyl radical intermediate does not appear to be viable as indicated by both energy barrier and endothermicity. The reaction would lead to benzene oxide/oxepin via hydrogen abstraction from the hydroxyl in the hydroxycyclohexadienyl radical intermediate operated by O2 as it exhibits a significantly higher barrier. Pathways A and B, on the other hand, present energy barriers of similar height. It was also observed that while B appears to be easily reversible, reaction A is not.

A Bacillus sphaericus monooxygenase capable of catalyzing the first two steps in the degradation of p-nitrophenol (PNP) via 4-nitrocatechol and 1,2,4-trihydroxybenzene (THB) was identified and characterized. Nitrite was produced stoichiometrically by PNP-grown cells. Results of the THB stimulation of oxygen consumption reveal that THB acts as a substrate for a ring cleavage dioxygenase. It was also observed that a single monooxygenase system was capable of catalyzing the initial hydroxylation of PNP and the oxidative release of the nitro group from the 4-nitrocatechol.

Pseudomonas strains with the ability to degrade isopropylbenzene (IPB) and tricholoroethane (TCE) are developed using an ipb DNA module. Results from the localization of transcriptional start points of the ipbA genes indicate that ipb gene expressions are regulated in response to IPB at the transcriptional level. The mutant Pseudomonas sp. strain JR1 exhibited the ability to efficiently degrade TCE after the induction of TCE-oxidizing oxygenase.

The initial 13C-13C nuclear magnetic resonance coupling in an aromatic annulene, except benzene, and the high-temperature automerizations similar to those previously noted in benzene systems were elucidated by synthesizing 1,2-di-13C-cyclooctatetraene. 13C's did not exhibit scrambling despite the occurrence of H2 decomposition and CH4 evolution. The results further revealed that the 1J(sub CH) and 1J(sub CC) couplings for the aromatic COT2- system of 145.9 and 55.8 are in agreement with results of other studies for 1,2-di-13C-benzene systems.

The products of the reaction of the 13C atoms with benzene and tert-butylbenzene were examined. Results showed that the reaction between atomic carbon and benzene rings forms phenylcarbenes by C-H insertion. Since the reaction was exothermic by approximately 115 kcal/mol., a possible rearrangement to the more stable cycloheptetraenes may occur. The results exhibited a different process from the reaction of C atoms with pyrrole which uses the double bond addition as the main process.

An efficient synthesis of several tris-, bis-, and mono-annelated benzenes based on the palladium-catalyzed coupling of three ethylenic units composed of alpha,beta-dibromoalkenes and alpha'-alkenyl Grignard reagents are described. The electronic origin of the Mills-Nixon effect was obtained by examining the electron-density distributions in the aromatic C-C bonds. Cyclic voltammetry was also used to investigate the intrinsic electron-donor properties of aromatic hydrocarbons.

The x-ray structures of a series of highly congested polyphenylbiphenyls and polyarylfluorenes are described. The symmetry of the planar drawings of polyphenylbiphenyls reflects D2 or D2d geometry and molecular mechanics calculations suggest that the D2 geometry is the conformation of the lowest energy. Although the central benzene ring is planar in the observed C1 structure, the other ring is distorted into a boat conformation. On the other hand, the phenylfluorenes exhibit large size and well-defined conformations after short and versatile syntheses.

A study was conducted on the benzene potential energy hyperface was explored using second-order perturbation theory, hybrid Hartree-Fock/density functional theory and the coupled-cluster method with single, double and perturbative triple excitations. Results revealed that there are three competing mechanisms for the high-temperature intramolecular topomerization of benzene. However, it was unlikely that benzene topomerizes at 1373 K exclusively via one mechanism since these mechanisms were all within 3.2 kcal mol.

A reinvestigation was conducted on a prototype literature arene hydrogenation system involving a [(C8H17)3NCH3]+[RhCl4]- ion pair catalyst using a four-step mechanistic approach. Results showed that Rh(0) nanoclusters are formed under reaction conditions and that benzene catalytic hydrogenation reaction follows nucleation and autocatalytic surface growth mechanism for metal(0) nanocluster growth. These suggest that benzene hydrogenation is heterogeneous in nature.

The optimized structures of tert-butyl alcohol and tert-butyl alcohol/benzene dimers were calculated by the ab initio method at the HF/6-311++G(d,p) level of theory. The local Moller-Plesset perturbation technique was employed for electron correlation energy corrections. Experimental results showed significant mode-sensitive differences in the relaxation mechanisms occurring in solution as indicated by correlation times and temperature-dependent line width analysis of two benzene infrared bands in several liquid tert-butyl alcohol/benzene mixtures.

A study was conducted on a novel nucleophilic polysubstitution reaction of hexachlorobenzene (HCB) with cyanide ion in acetonitrile/water. The findings indicate that an electron acceptor is not required for successive photocyanations of HCB with high quantum yield. Sensitization and quenching results suggest a triplet reactive excited state. However, variation of [HCB] at constant [CN-] indicates that the reaction becomes less efficient with increasing [HCB].

A study investigates the rate-limited sorption of homologous series hydrophobic organic compounds such as polycyclic aromatic hydrocarbons, alkylated benzenes, chlorinated benzenes and chlorinated alkenes by two soils with humic and fulvic acid. Results revealed that the solutes sorbed more strongly to the humic-dominated soil than the fulvic-dominated soil. Sorbate shape and structure appear to have a secondary influence on the total equilibrium sorption.

Group-transfer reactions with ethane were studied to determine the effect of substituents on the energies of phenyl derivatives. Bond dissociation energies of both phenyl and vinyl derivatives indicate similarities between the interaction of substituents with benzene and ethylene. This was supported by information derived from electron-density difference plots and rotational barriers. Instances wherein fluorine becomes a pi-donor were presented.

A study was conducted to evaluate the efficiency of a one-pot system that can catalytically dehalogenate highly-chlorinated aroclors and benzenes at reasonable conversion rates. The system utilizes THF as solvent, PdCl2(dppf) as catalyst, NaBH4 as reducing agent and TMEDA as a supporting base. Results on dechlorination efficiency and regioselectivity were considered satisfactory.

The flow cell, Schmidt-Milverton plots and microgravity conditions were used to obtain measurements of the Soret coefficients of aqueous solutions of methyl, ethyl, isopropyl and n-butyl alcohols and of solutions of methyl and ethyl alcohols in benzene. The signs of the Soret coefficients for all three methods were found to be the same for all organic solutions. Results also showed that for large Soret coefficients, a convective phenomenon appears in the flow cell for both positive and negative separation factors.

The neutral benzene (C6H6) on Ag{111} was subjected to 8 kiloelectronvolt ion bombardment to investigate the time-of-flight (TOF) distributions, angular distributions and relative sputtering yields of the ejected C6H6 molecules. Two components were found to be present in the TOF distributions derived using Ag+ ion as the projectile. The C6H6 kinetic energy and angular distributions at low coverage were found to exhibit similar characteristics with the Ag particles ejecting from the substrate. The largest total yield of the ejected C6H6 molecules was observed for a monolayer coverage.

A study using single-crystal X-ray diffraction and solid-state 15N NMR spectroscopy examined an azobenzene dyestuff which goes through conformational exchange in the solid state. The combined utilization of the two techniques provided a thorough understanding of the disordered character of a common azobenzene dyestuff. The X-ray analysis demonstrated two conformations with an almost equal weighting within the asymmetric unit. Meanwhile, solid-state NMR showed that a motional process that interconverted two trans conformations on a time scale influenced the quality of the disorder.

Mass-analyzed threshold ionization spectroscopy is used to quantify ionization energies of indole-argon (62505 cm-1), indole-water (59433 cm-1) and the indole-benzene (59833 cm-1) complexes and their dissociation energies in the cationic ground state. With the use of a highly sensitive MATI detection scheme, the study offers the first determination of the decomposition threshold of a hydrogen-bonded ionic complex. The van der Waals bound indole-Ar complex was also measured. The findings are discussed.

The use of tert-butyl and trimethylsilyl substituted cyclobutenediones allowed the synthesis of 2-unsubstituted hydroquinone monoacetates, quinones and 3-unsubstituted quinolizinones in moderate to high yields. The addition of unsaturated carbon nucleophiles occurred regiospecifically at the carbonyl group farthest from the tert-butyl or trimethylsilyl substituent. Very efficient removal of the tert-butyl group was performed under very acidic conditions.

A study was conducted to examine conductivity measurements on a monolayer of thiotolane molecules that were self-assembled on a gold surface. Optimized geometrics and relative energies for three conformations and ions were also analyzed in the study. Results indicated that conductivity was determined by the relative angle between two benzene rings in each tolane molecule. Findings also showed that the rings in the tolane molecules started rotating at temperatures between 10 and 30 K.

The proton and methyl cation affinities of benzene and its di- and polysubstituted analogues were investigated at the MP2(fc)/6-31 G**//HF/6-31G*+ZPE(HF/6-31G*) theoretical level. Experimental results showed that methyl cations of polysubstituted benzenes follow the additivity rule, which is similar to the additivity property of protons in multiply-substituted aromatics. The additivity approach is based on the independent substituent approach and is very suitable due to its high performance, simplicity and intuitive appeal.

The stacking interactions of phenyl-perfluorophenyl seen in benzene/hexafluorobenzene were investigated in terms of their supramolecular motif. The phenyl-perfluorophenyl interaction was utilized to adapt olefinic molecules in the crystalline state. The face-to-face interaction of phenyl/perfluorophenyl group was observed to induce the geometry of crystallization producing photoreactive crystals. The interaction oriented the reactive olefinic moieties making photochemical cycloaddition reaction possible.

A study was conducted to examine the macrolactonization of trichloroethyl ester derivatives determined by potassium salts. Tetrahydrofuran and benzene were harvested from sodium/benzophenone. The effects of various esters on the cyclization reaction was also analyzed. Results indicated that the rate-limiting step of a transesterification correlated with the addition of alcohols of alkoxide fragments to the carbonyl carbon.

A study was conducted to characterize novel electrophilic trifluromethylating agents determined from cheap reagents. A 200 MHz nuclear magnetic resonance (NMR) spectrometer was utilized to determine 19F, 1H and 13C NMR spectra while triflate derivatives were determined by an intermolecular condensation reaction. Results indicated that the electrophilic trifluoromethylating potential can be changed by integrating electron-widthdrawing substituents on the benzene rings.