摘要:

Theoretical studies ofπ-electron structures of triplet states of mono andp-di-substituted benzenes with the electron-donating groups, OCH3and N(CH3)2, were carried out by considering configurational interactions between the locally excited triplet configurations of benzene and the intramolecular charge-transfer (or electron-transfer) triplet configurations. Assignments of the triplet-triplet absorption spectra reported forN,N-dimethylaniline andN,N,N′,N′-tetramethyl-p-phenylenediamine are made on the basis of the present theoretical results of transition energy and oscillator strength. From the present study, it is concluded that the T-T absorption bands of DMA and TMPD appearing in the visible region are so-called ‘intramolecular charge-transfer bands’.

ISSN:0026-8976    

DOI:10.1080/00268976800100881

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

A modified Mataga SCF method is applied to the azines. Parameters obtained from single ring molecules are used to generate spectra and physical properties for acridine and phenazine. Symmetry considerations point out that only a minimum of configuration interaction (CI) is necessary.

ISSN:0026-8976    

DOI:10.1080/00268976800100891

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Expressions are derived for the effects of magnetically anisotropic discshaped or rod-shaped solvent molecules on the nuclear screening in a spherical solute molecule, using a model in which the solute and solvent molecules are represented respectively by a hard sphere and a disc or rod which interact only when they collide. The expressions are functions of the dimensions of the sphere and of the disc or rod, but are independent of the position within the solute molecule of the nucleus under observation. The predicted effects are compared with measurements of the differential solvent shift between carbon tetrachloride and benzene for the solutes methane, tetramethylsilane and cyclohexane. The model satisfactorily accounts for the qualitative dependence on the radius of the solute molecule, but predicts solvent shifts approximately twice as great as those observed. It is suggested that the discrepancy results from neglecting attractive van der Waals forces.

ISSN:0026-8976    

DOI:10.1080/00268976800100901

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Suitable forms of coordinates for torsional lattice vibrations are discussed. It is shown that infinitesimal rotation coordinates may be used if their ‘hidden’ redundant character is allowed for. Examples of the form of typical torsional force constants are given.

ISSN:0026-8976    

DOI:10.1080/00268976800100911

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The bond electronegativity equalization method forσbonds is combined with the Hückel molecular orbital method forπbonds to give a SCFσ-πtreatment for conjugated molecules. The method, BEEM-π, is used to calculate the nuclear quadrupole frequencies of35Cl in conjugated systems; the frequencies agree well with experiment.

ISSN:0026-8976    

DOI:10.1080/00268976800100921

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

An examination is made of the effect of rapid specimen rotation on the N.M.R. spectra of solid specimens, with particular reference to the anisotropic electron-coupled spin-spin interaction. It is shown that when the specimen is rotated rapidly about an axis inclined at the special angle of 54° 44′ to the direction of the external magnetic field the spectral broadening arising from any anisotropy of the electron-coupled spin-spin interactions is removed provided the coupling tensors are symmetric. The dipolar interactions and the anisotropy of the chemical shift tensors are of course removed also, and the spectra are in such cases determined by the scalar shifts σ and coupling constantsJas in isotropic fluids. It is however found that when a spin-coupling tensor has an antisymmetric component, this component is not in general removed by the rapid rotation. The spectrum is then determined by antisymmetric coupling constantsAin addition to σ andJ. A discussion is given of the role played by the constantAin the determination of the N.M.R. spectra.

ISSN:0026-8976    

DOI:10.1080/00268976800100931

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The Raman spectra of chloroform, trichloromethyl fluoride and trichloromethyl cyanide have been studied as pure liquids and as solutions in various solvents. In particular the isotope patterns of thosea1modes which involve mainly chlorine vibrations have been studied as a function of concentration in cyclopentane. In certain bands of the pure liquids where the isotope structure is well resolved this structure is not consistent with species containing three equivalent chlorine atoms. Pure CFCl3possesses bands which exhibit both this anomalous pattern and the expected pattern. On dilution in a wide range of solvents the anomalous bands revert to the expected pattern and the normal bands are unaffected. The anomalous patterns observed and the behaviours on dilution were identical for all three compounds. This evidence has been interpreted on the basis of association in the pure liquids though the specific nature of the interactions involved depends on the compound.

ISSN:0026-8976    

DOI:10.1080/00268976800100941

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The electron spin resonance spectra of several alkoxybenzene radical anions produced by the potassium and caesium reduction of the parent compounds in ethereal solvents are presented.π-electron molecular orbital calculations of spin densities have been made for these systems, as well as for the toluene and p-xylene radical anions, and assessed from the account they give of the proton and carbon-13 hyperfine splittings. The unrestricted Hartree-Fock approach with spin annihilation gives results in best agreement with experiment. Vibronic mixing is considered and concluded to be small for the alkoxybenzene anions. Metal hyperfine splittings have been observed in the caesium-anisole and caesium p-dimethoxybenzene systems and their temperature dependence measured. The results are considered in relation to the structure of the ion pairs.

ISSN:0026-8976    

DOI:10.1080/00268976800100951

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The gas phase electron resonance spectrum of NS in theJ=3/2 level of the2π3/2 state is described. The theoretical analysis of the spectrum is developed using the irreducible tensor method and values of the14N hyperfine and quadrupole coupling constants are determined. Application of a static electric field produces a first-order Stark splitting in the spectrum and analysis yields the electric dipole moment of the radical.

ISSN:0026-8976    

DOI:10.1080/00268976800100961

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

N.M.R. spectra of ortho dibromo, dichloro and dicyano benzenes have been studied in liquid crystalline nematic phases. The spectra have been analysed iteratively. The direct couplings are found to be of opposite sign compared to the indirect ones. Ratios of the various inter-proton distances in these molecules are determined. They do not deviate significantly from the corresponding ratios in unsubstituted benzene.

ISSN:0026-8976    

DOI:10.1080/00268976800100971

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor