摘要:

The preparation of solutions thought to contain simple aliphatic carbonium ions is described and their spectra recorded. Alternative explanations are considered, and the nature of the electronic transition is discussed.

ISSN:0026-8976    

DOI:10.1080/00268976000100251

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

The ground state wave function of a hydrogen atom in an electric field-gradientF' is obtained, correct to the first power inF', and the nuclear magnetic screening constant σ evaluated. TheF' contribution to σ vanishes if all directions ofF' relative to the applied magnetic field are equally probable. In part (2), the influence of a uniform compression of the H-atom on σ is examined. This effect, which will predominate at sufficiently high pressures, causes a decrease in the electronic polarizability but an increase in σ.

ISSN:0026-8976    

DOI:10.1080/00268976000100261

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

The proton resonance spectra at 40 Mc/s of solutions of symmetrically substituted dimethylnaphthalenes in carbon disulphide have been measured and interpreted. Methyl substitution causes changes of the chemical shifts of the various ring protons, which are discussed in terms of the inductive effect of the methyl group. It is shown that a correlation exists between the variations of these chemical shifts and the partial rate factors for H-D exchange.

ISSN:0026-8976    

DOI:10.1080/00268976000100271

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

In a radical the single determinant wave function which gives the lowest electronic energy is one where electrons of opposite spins occupy different sets of molecular orbitals and thereby lower the ‘exchange’ part of the energy. The unpaired spin density may be negative in a wave function of this type and is easily found by perturbation theory if certain exchange integrals are small. We show that the spin density is then almost the same as one finds by combining the usual single determinant function (with one unpaired electron, and 2npaired ones innorbitals) with its singly excited doublet configurations. In alternant hydrocarbons the Pariser and Parr theory leads to a simple formula for the spin density:ρr=cro2- λ Σsπrscso2, wherecrois the Hückel coefficient of the odd orbital on atomr,πrsis the mutual polarizability of atomsrands, and λ is a constant derived from the theory. The observed hyperfine structure in the electron resonance spectra of naphthalene, anthracene, perylene, diphenyl, phenanthrene, and pyrene negative ions agrees well with this formula, provided the constantQdefined by McConnell is about -24·2 gauss. The non-alternant negative ions of acenaphthylene and fluoranthene also agree, but not acepleiadylene. The theory predicts identical spin densities in corresponding positive and negative ions. In neutral alternant radicals we find negative spin densities on all the unstarred atoms of triphenylmethyl, perinaphthenyl, allyl, and benzyl. The calculated negative densities are a little too small to fit the spectra of the first two radicals, but fit just as well as valence bond ones.

ISSN:0026-8976    

DOI:10.1080/00268976000100281

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

Changes in the nuclear magnetic resonance spectra of dimethyl-formamide and dimethyl-acetamide have been studied in various solvents over a range of concentrations. It is shown that addition of aromatic solvents causes the relative chemical shifts of the two methyl resonances to change sign. This shows that no rapid reorientation of the dimethyl amino group occurs in these solutions at room temperature, and the shifts observed are interpreted in terms of the formation of loose complexes between the amide and the aromatic molecule.

ISSN:0026-8976    

DOI:10.1080/00268976000100291

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

The experimental behaviour of the classical fluctuation discriminant of the configurational energy and the virial is examined for the fluid states of nitrogen and methane. This discriminant must be essentially positive. It is found that the assumption of a Lennard-Jones 12 : 6 potential leads to negative values of the discriminant for the orthobaric liquids at low temperatures, for the liquids at high pressures, and, probably, for the gases at high temperatures. These results confirm those found previously for argon, and demonstrate the inadequacy of the 12 : 6 potential at high densities and temperatures.

ISSN:0026-8976    

DOI:10.1080/00268976000100301

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

The temperature-independent paramagnetism of permanganate is discussed in terms of molecular orbital theory. It is shown that the major contribution to the paramagnetism arises from electrons in metaldorbitals, and that the amount of charge-transfer from the ligands to the metal ion can be estimated. The theory is applicable to any complex in which the metal ion possesses vacant low-lyingdorbitals.

ISSN:0026-8976    

DOI:10.1080/00268976000100311

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

In 1954, I. Prigogine and the present author established that the time derivative of the entropy production, for constant values of the fluxes, is always negative or zero when the boundary conditions of the system are stationary. However, mechanical equlibrium was postulated and it follows that the dissipative forces were not taken into consideration but only the other cases of irreversibility (chemical reactions, heat and diffusion). In this work the above limitation is eliminated. The system, however, is assumed to be in mechanical steady flow during the whole process.

ISSN:0026-8976    

DOI:10.1080/00268976000100321

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

V,W, andXcoefficients analogous to Racah's⫫,[Wbar]and[Xbar]coefficients and Wigner's 3j, 6jand 9jsymbols are defined for certain finite groups and their properties examined. Tables of values of these coefficients are given for the one-valued representations of the octahedral group.

ISSN:0026-8976    

DOI:10.1080/00268976000100331

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

ISSN:0026-8976    

DOI:10.1080/00268976000100341

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor