Polarized Raman Spectra VII Correlations and Assignments of Raman Lines in p-Polyphenyls

The Raman spectra of powdered biphenyl, p-terphenyl, and p-quaterphenyl are compared with each other and also with the Raman spectrum of benzene. Most Raman lines in polyphenyls can be considered as derived from normal vibrations in benzene. The intense lines are thus assigned and the correlations between them are established.     

The pressure dependence of the low-frequency Raman spectra of crystalline biphenyl and p-terphenyl

Raman spectra as a function of hydrostatic pressure are presented for crystalline biphenyl and p-terphenyl. The observed changes in the low-frequency Raman spectra of crystalline biphenyl indicate that there are probably some changes in the crystal or molecular structure with increasing pressure. The Raman spectra of p-terphenyl have no evident anomalies at pressures up to 33 kbar.     

Intermolecular interactions and geometry of non-rigid molecules in weak crystalline complexes: Vibrational spectra of 4,4′-dinitrobiphenyl complexes with biphenyl,biphenyl derivatives and p-terphenyl

Raman spectroscopy is used to study the complexes of 4,4′-dinitrobiphenyl with biphenyl, 4-hydroxybiphenyl, 4-bromobiphenyl and p-terphenyl, which crystallize in a highly unusual geometry. Their phonon spectra at 125 K and 18 K are compared and the effect of isotopic substitution of biphenyl on the phonon spectra of its complex is examined. Internal vibrations of the components in the crystalline complex are compared with those observed in the pure crystals of the components. The results from both phonon and intramolecular vibration studies show that these complexes form in fixed stoichiometries, are governed by geometrical factors, and are stabilized primarily by van der Waals interaction, although other kinds of interactions may provide additional stabilization. The 4,4′-dinitrobiphenyl molecule as well as biphenyl and p-terphenyl are centrosymmetric and remain so when the complexes are cooled from room temperature to 18 K. For biphenyl complex, this conclusion is supported by the observed IR spectra which show mutual exclusion between IR-active and Raman active vibrations. Crystal splitting is observed on the 410 cm^?1 vibration of 4,4′-dinitrobiphenyl. This splitting is attributed to the presence of more than one 4,4′-dinitrobiphenyl molecules in the complex unit.     

Analysis of the terphenyls by a compressed pellet infrared method involving micro-distillation

A quantitative compressed pellet infrared method used together with a micro-distillation to effect separation of the isomer has been developed and reported here for the analysis of ortho-, meta-, and para-terphonyl. The terphenyl content is determined on fractions isolated by distillation from radiation damaged samples. The compressed pellet infrared method is preferred instead of the more conventional solution technique since smaller quantities of isolated terphcnyl are required. The pellet method is applicable also to polyphenyls higher than the terphenyls. The solution technique is not due to the insolubility of the polyphenyls. It is expected that the compressed pellet spectral method developed here might well find application in the analysis of compounds other than polyphenyls. Results presented here appear to be the, first quantitative infrared data reported in the literaturu on polyphenyl compounds.     

Electroactive polymeric films from oxidative coupling of oligophenyls

Anodic coupling of biphenyl, terphenyl and triphenylene in acetonitrile was investigated by electrochemical and spectroscopic techniques. Ortho-terphenyl cyclization to triphenylene is followed by two-graft linking in a polyparaphenylene-like structure which is reversibly oxidized with 0.5 electrons per monomer. Para-terphenyl produces a structure containing both polyparaphenylene segments and triphenylene islands. Meta-terphenyl and biphenyl give more disordered structures with dominance of triphenylene-like moieties.     

The aggregation behavior of O-carboxymethylchitosan in dilute aqueous solution

O-Carboxymethylchitosan (OCMCS) is a kind of biocompatible derivatives of chitosan whose water solubility is strongly dependent on the degree of carboxymethylation. The OCMCS with 100 carboxymethyl groups and 75 amino groups per 100 anhydroglucosamine units of OCMCS was synthesized by the reaction of chitosan and monochloroacetic. When OCMCS was dissolved in water, its solution was neutral and OCMCS behaved like a weak polyanionic polyeclectrolyte because most of carboxylic groups were not dissociated in neutral aqueous solution. The aggregation behavior of OCMCS in aqueous solution was studied by surface tensiometry, steady-state fluorescence spectroscopy and viscometry. The critical aggregation concentration (cac) of OCMCS was determined to be between 0.042 mg/ml and 0.050 mg/ml. The possible aggregation mechanism of OCMCS in water was elucidated.     

Calculation of molecular polarizabilities: the indo method applied to some aromatic hydrocarbons1

Molecular polarizabilities calculated by the all valence electron INDO method are reported for benzene, naphthalene, anthracene, phenanthrene, biphenyl and p-terphenyl. For these molecules INDO is better than other semi-empirical methods at predicting the polarizability anisotropy.     

Effective molecular polarizabilities in some aromatic hydrocarbon crystals

Two equivalent methods of calculating effective molecular polarizabilities from crystal electric susceptibilities are compared. For monoclinic crystals containing two molecules per unit cell, there is no unique solution. The range of solutions is examined for naphthalene, anthracene, biphenyl, p-terphenyl and phenanthrene, treated as polarizable points. For all these molecules the largest polarizability component is unacceptable, owing to the point molecule approximation. When the interactions between molecules are calculated as averages between aromatic rings, more realistic polarizabilities result, showing variations consistent with the molecular geometry. Comparable results are obtained for benzene (orthorhombic). It is concluded that reliable polarizabilities should become available by developments of such an approach.     

Hydrogenation of biphenyl and isomeric terphenyls over a Pt-containing catalyst

Catalytic hydrogenation of benzene, biphenyl, and ortho-, metha-, and para-isomers of terphenyl over a 3 wt.% Pt/C at 180 °C and 70 atm was studied. The directions of hydrogenation of each substrate were revealed. Relationships between structures of the substrate and hydrogen consumption rates were found. It was shown that hydrogenation rate decreases on going from benzene to terphenyl and with increasing degree of the substrate hydrogenation. Hydrogenation rate of terphenyl isomers decreases in the following order: p-terphenyl > > m-terphenyl > o-terphenyl.     

Intramolecular band mapping of poly(p-phenylene) via UV photoelectron spectroscopy of finite polyphenyls

Ultraviolet photoelectron spectra were measured of solid sexiphenyl with synchrotron radiation and of gaseous polyphenyls from biphenyl to sexiphenyl with a Hel light source. The similarity of the spectrum of the solid with the XPS spectrum of poly(p-phenylene) (PPP) shows the usefulness of sexiphenyl as a model compound of PPP. Examination of the fine structure observed in the low binding-energy region clearly shows how the electronic structure of the p-phenylenes evolves from that of benzene including the effects of deeper levels and of the non-planarity of the molecular geometry. The experimental E = E(k) energy band-dispersion relation of a PPP chain can be deduced by giving each energy level of the oligomers an appropriate k value. An extrapolation for the total bandwidth and the threshold photoemission energy of solid PPP yields 3.9₅ and 5.6₅ eV. respectively.     

Thermal degradation mechanisms of liquid crystalline aromatic polyesters studied by pyrolysis–gas chromatography/mass spectrometry

The thermal degradation mechanisms of liquid crystalline aromatic polyesters (LCPs) prepared from p-hydroxybenzoic acid (PHB), biphenol (BP), and terephthalic acid (TA) were studied by pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS). The LCP containing deuterated terephthalate units and the LCPs that have different comonomer ratios were examined. On the basis of the pyrolysis products determined, the origin of the main pyrolysis products (benzene, phenol, biphenyl, phenyl benzoate, etc.) from the corresponding comonomer units were estimated and their thermal degradation mechanisms were eventually discussed in detail.     

The influence of molecular geometry on the fluorescence spectra of biphenyl and the polyphenyls

The shapes of the fluorescence spectra of rigid solutions (in ethanol at 77 K) of biphenyl,p-terphenyl, andp-quaterphenyl are shown to depend on the wavelength of the exciting light: the spectral resolution enhances with increasing wavelength of excitation. These spectra are interpreted in terms of a model wherein the equilibrium configuration of the fluorescent state is planar, but that of the ground state deviates from planarity.Some other results reported in the literature are also discussed and it is concluded that the ground states of the singly and doubly charged ions of these molecules, as well as the lowest triplet states of the neutral molecules, are nearly planar.     

不同涤纶绳索纤维的PY-GC/MS定性分析

利用裂解-气相色谱/质谱联用法对9个不同产地、不同规格的涤纶绳索样品进行鉴别分析.首先通过优化选择,确定试验条件,即裂解温度为550℃、裂解时间为6 s时,柱程序升温条件为50℃(1 min)20℃/min→250℃(10 min).在此条件下可最大限度的显示涤纶裂解产物的特征.9个样品的裂解分析结果显示,涤纶的主要裂解产物有13种,其中特征裂解产物为苯甲酸(相对强度100%)、苯甲酸乙烯酯、联苯、苯等.虽然9个涤纶绳索有相同的裂解特征,但个别裂解产物及各特征裂解产物的相对含量有所不同.这一差异可以作为不同规格、不同产地涤纶绳索分析鉴别的依据.     

The determination of copper in sea water by atomic absorption spectrometry with a graphite atomizer after elution from chitosan

Copper in sea water was determined by passing 1 1 of persulphate-pretreated sea water through a 30×3 mm chitosan column, and eluting with 20 ml of a 1% solution of 1,10-phenanthroline, or with 20 ml of 1 M sulphuric acid. Copper was determined in the eluates by hot graphite atomic absorption spectrometry. The result for Adriatic sea water (Ancona, Italy) was 6.06±0.56 μg Cu 1^?1. Diethylaminoethylcellulose, p-aminobenzylcellulose and Dowex A-1OO were also tested; Dowex A-100 collects only a minor part of the copper present in sea water.     

Hierarchical self-assembly of p-terphenyl derivative with dumbbell-like amphiphilic and rod-coil characteristics

As water is gradually added, a p-terphenyl derivative with dumbbell-like amphiphilic and rod-coil characteristics can hierarchically self-assemble to metastable rectangle columns architecting sheets first and then to stable quasi-hexagonal columns architecting rolled sheets, and finally to rod-like nanostructures in MeOH/H₂O solution. Interestingly, the formed sheet, rolled sheet, and nanorod possess blue-light emitting property.     

Formation of isomeric terphenyls and triphenylene by pyrolysis of benzene

The pyrolysis of benzene has been investigated at 773, 923, and 1073 K and the mechanisms of formation of isomeric terphenyls and triphenylene have been studied, the results being compared with those obtained by pyrolysis of benzene solutions containing diphenyl and o=terphenyl. No differences in the mechanisms of the formation of terphenyls and triphenylene could be observed at the selected temperatures, even if ring fission and a higher degree of polymerization occurred at 1073 K. The addition of diphenyl and o-terphenyl showed that the reactions leading to the formation of isomeric terphenyls and triphenylene in the pyrolysis of pure benzene do not pass through stable intermediates.     

Regioselectivity control of photodimerization of liquid-crystalline cinnamoyl compounds by phase variation: dual functionality of p-terphenyl substituent as a mesogen and a triplet sensitizer

Cinnamoyl-functionalized liquid-crystalline (LC) compounds having a 4″-substituted [1,1′;4′,1″]terphenyl (p-terphenyl) as mesogens were synthesized to investigate the abilities of the mesogen to act as a triplet sensitizer. UV (365 nm) irradiation of the LC compound having 4″-cyano-p-terphenyl in the crystalline and LC phases regioselectively produced the photodimers with a head-to-tail and a head-to-head cyclobutane unit, respectively. The p-terphenyl thus played the role of triplet sensitizer because the cinnamoyl group does not absorb 365 nm light. Due to the dual functionality of the p-terphenyl as the mesogen and the triplet sensitizer, we successfully performed the photochemical and regioselective cycloaddition to obtain two different LC dimers from one LC monomer.     

The triplet state of picene in p-terphenyl crystals by EPR

Spin-hamiltonian parameters of the triplet state of picene in p-terphenyl crystals are determined. Optical spin polarization and transient nutations are also observed using pulsed light sources.