Molar Cotton-Mouton Constants Research Articles

Anisotropy of magnetic susceptibility and molar Cotton-Mouton constants of six anilines and 1,3,5-trimethylhexahydro-1,3,5-triazine

The semiaxes of the magnetic susceptibility ellipsoid were determined for the Ph-N fragment in 4-substituted anilines and N,N-dimethylaniline. Deviations from additivity due to the additional paramagnetic contribution in a direction perpendicular to the plane of the aromatic ring were found.

Molar cotton-mouton constants and anisotropy of magnetic susceptibility of benzyl chlorides and benzyl bromides

Due to theπarom−gsC-Hal* interaction, the magnetic susceptibility ellipsoids of α-haloalkylbenzenes, with the exception of α,α'-p-xylylidene bromide, undergo rearrangement of the semimajor axes with a decrease in the diamagnetic component in direction 1, 4 and along the axis of symmetry of the π electrons in the ring.

Molar cotton-mouton constants of liquid haloalkanes and nonadditivity of the conformational energies of methylated chloro-, bromo-, and iodopropanes

1. The molar Cotton-Mouton constants of chloro-, bromo-, and iodopropanes and their methylated derivatives have been determined by a method involving measurement of the magnetic birefringence, and the conformational composition of the molecules investigated has been established. 2. The nonadditivity of the potential interactions of vicinal C-CH3 and C-Hal substituents has been analyzed. The dominant role of the orbital effects in the stabilization of asymmetric gauche conformations of the molecules of the halopropane series has been revealed.

Anisotropy of the magnetic susceptibility of the carbonyl group and molar cotton-mouton constants for aromatic aldehydes and ketones

1. From the molar Cotton-Mouton constants for acetone and cyclohexanone, we determined the magnetic susceptibility tensor for the C=O bond, which is paramagnetic in the plane of the carbonyl and diamagnetic in the perpendicular direction. 2. Within the framework of the tensor additive scheme, we calculated the theoretical molar Cotton-Mouton constants (which agree with experimental data) for aryl-containing aldehydes and ketones. This confirms the additive nature of the molecular magnetic susceptibility tensor for the studied compounds.

Anisotropy of the magnetic susceptibility of the C-O bond from cotton-mouton effect data for anisoles and 1,4-dioxane

1. From the molar Cotton-Mouton constants of anisoles and 1,4-dioxane, we calculated the anisotropy of the magnetic susceptibility for the Csp2−0 and Csp3−0 bonds. 2. We have determined the influence of conjugation and hybridization effects on the diamagnetic susceptibility tensor for the C-O bond.

The temperature dependence of the Cotton-Mouton effect of N2, CO, N2O, CO2, OCS, and CS2 in the gaseous state

Abstract The magnetic-field-induced birefringence of the six substances N 2 , CO, N 2 O, CO 2 , OCS, and CS 2 has been measured in the gaseous state, between −70 and +120 °C and at pressures up to 1 bar. A quantum correction term, accounting for the influence of the rotation-induced magnetic moments, is derived to modify the expression from classical orientation theory describing the Cotton-Mouton effect of linear molecules. The temperature dependence of the measured molar Cotton-Mouton constants m C ( T ) has been analyzed in terms of the hyperpolarizability anisotropy parameter Δη and the orientation parameter ΔαΔξ. The latter is discussed in view of the polarizability and susceptibility anisotropies Δα and Δξ and of electric quadrupole moments Q ??? known by other techniques. There is generally good agreement between results from Rayleigh scattering, high-resolution spectroscopy, electric-field-gradient-induced birefringence, and the present Cotton-Mouton effect results.

Cotton ? Mouton constants and the anisotropy of the magnetic susceptibility of substituted benzenes

1. An equation has been proposed for the calculation of molar Cotton-Mouton constants from solution data. 2. The magnetic susceptibility ellipsoids of C-Cl and C-Br bonds and of the C-CH3 groups in a number of substituted benzenes have been found.

The temperature dependence of the cotton-mouton effect of ethane, ethene and ethyne

The magnetic-field-induced birefringence of the three gases ethane, ethene, and ethyne has been measured between −80 and +120°C, at pressures up to 1 bar. The molar Cotton-Mouton constants depend linearly on the reciprocal absolute temperature which is in agreement with the well-known theory for non-interacting molecules. Magnetic hyperpolarizability anisotropy parameters, susceptibility anisotropies, and some secondary quantities of these molecules have been determined for the first time.

Cotton-Mouton and Kerr constants of twelve non-dipolar tri- and hexa-substituted benzenes

Measurements of the infinite-dilution molar Cotton-Mouton and Kerr constants of 12 non-dipolar 1,3,5-tri- and hexa-substituted benzenes as solutes in carbon tetrachloride at 298 K are reported. Some of the experimental results are in notable disagreement with earlier determinations made on equipment of much lower sensitivity. Although the magnetic anisotropies derived for the tri-substituted benzenes are concordant with other observed or predicted values, those for the hexa-substituted benzenes are generally very much larger than expected. It is suggested, in explanation, that relatively large and strongly anisotropic atomic polarizabilities may cause the ratio of the static to the high-frequency polarizability anisotropy to be considerably smaller in the hexa-substituted benzenes than in benzene; in addition, there may be significant temperature independent contributions to the magnetic birefringences of these molecules.

Magnetic anisotropies and relative aromaticities of pyrrole, pyrazole, imidazole and their N-methyl derivatives

Experimental dipole moments, molar Kerr constants and molar Cotton-Mouton constants at 298 K and 633 nm are reported for pyrrole, pyrazole, imidazole and their N-methyl derivatives as solutes in dioxan. Analysis of the Kerr-effect data yields the effective polarizability anisotropies which are used to evaluate the molecular magnetic anisotropies from the Cotton-Mouton constants. The magnetic criterion of aromaticity is applied by estimating for each molecule the non-local contribution to the out-of-plane component of the magnetizability and the magnetic anisotropy. Electron delocalization in these molecules is significantly less than that exhibited by benzene: pyrrole and N-methylpyrrole, c. 70%; pyrazole and N-methylpyrazole, c. 65%; imidazole and N-methyl-imidazole, c. 60%. Approximately one-third of the observed magnetic anisotropy arises from localized contributions.

Molecular magnetic anisotropies from the Cotton–Mouton effect

Improved equipment for measuring magnetic and electric birefringence in liquids and solutions is described. Molar Cotton–Mouton constants and molar Kerr constants at 298 K and 632.8 nm are reported for four model species (benzene, carbon disulphide, chloroform and pyridine) dissolved in each of three non-dipolar solvents (carbon tetrachloride, cyclohexane and dioxan). A careful analysis of the data yields the magnetic anisotropies of the solutes and illustrates the advantages and limitations of dilute–solution birefringence measurements as a route to this quantity.

Kerr constants, Cotton–Mouton constants, and magnetic anisotropies of pyridazine, pyrimidine, and pyrazine

Experimental dipole moments, molar Kerr constants, and molar Cotton–Mouton constants obtained at 298 K and 633 nm are reported for pyridazine, pyrimidine, and pyrazine as solutes in dioxan and cyclohexane. Analysis of the Kerr-effect data yielded the effective polarisability anisotropies, which were then used to evaluate the molecular magnetic anisotropies from the Cotton–Mouton constants. The magnetic criterion of aromaticity was applied by estimating for each diazine the non-local contribution to the out-of-plane component of the magnetisability. Progressive replacement of –CH by –N causes a considerable reduction inelectron delocalisation and, by inference, aromaticity in the order benzene > pyridine ≈ pyridazine ≈ pyrazine > pyrimidine > s-triazine.

Molecular conformations from magnetic anisotropies

A method is developed for determining molecular conformations through analysis of experimental molar Cotton-Mouton constants in conjunction with known anisotropic magnetic susceptibilities and electric polarizabilities for structural groups. Molar Cotton-Mouton constants (× 1016 e.m.u.), and derived interplanar angles, for molecules as solutes in carbon tetrachloride at 20°C are: biphenyl (+ 70, 0°); 2,2′-bipyridyl (+ 76, 25°); 9,9′-bianthryl (+160, 62°); 9-phenylanthracene (+ 157, 70°); 1-phenylnaphthalene (+79, 66°); 1,3,5-triphenylbenzene (+169, 35°).

Theory of the solvent effect on the molar refraction, polarization, Kerr and Cotton-Mouton constants of non-polar solutes

Classical statistical-mechanical theories for refractivity, dielectric polarization, and the Kerr and Cotton-Mouton effects are extended to examine interactions between anisotropic non-dipolar solutes and isotropically polarizable solvent molecules. These solvent effects are related to molecular polarizabilities and susceptibilities by correlation tensors which describe the anisotropy in the molecular distribution near a solute molecule. The solvent effects on molecular refraction and dielectric polarization are normally small but they may be large in the Kerr and Cotton-Mouton effects.

Molecular susceptibility. Molar Cotton-Mouton constants of liquids

Molar Cotton-Mouton constants, mCliq, are reported for about 40 pure aliphatic liquids. For some of these substances infinite dilution values, ∞(mC2), are also recorded. The relationship between mClig and ∞(mC2) is investigated for both aliphatic and aromatic liquids.

The stereospecific solvation of non-polar organic solutes in liquid benzene

The molar Cotton-Mouton constants of several non-polar and axially symmetric solutes have been measured in both benzene and carbon tetrachloride. Differences between the Cotton-Mouton constants of the same solute in these two solvents are largely attributable to angular correlations between the solute and the benzene molecules. Hexafluorobenzene and 1,3,5-trinitrobenzene reveal pronounced tendencies towards parallel alignment of solute and neighbouring benzene molecules.

Molecular susceptibility. The diamagnetic anisotropies of some polynuclear aromatic hydrocarbons

Molar Cotton-Mouton constants are reported for certain aromatic hydrocarbons as solutes at infinite dilution in benzene or carbon tetrachloride. Relative anisotropies (i.e. the ratio of the anisotropy in the diamagnetic susceptibility of the molecule concerned to that of benzene) are calculated for these and other molecules for which data have been recorded previously.1

Molecular polarisability and susceptibility. The conformation of triphenylboroxin

Molar Kerr constants and molar Cotton–Mouton constants are reported for trimethylboroxin and triphenylboroxin in benzene solution. The principal polarisabilities and susceptibilities are derived from the experimental results and analysed to indicate a planar or near-planar structure for triphenylboroxin.

Molecular susceptibility. The relative ring currents in pyridine, thiophen, furan, and pyrrole

Molar Cotton-Mouton constants at infinite dilution in carbon tetrachloride are reported; from these, in conjunction with available polarizability and susceptibility data, the diamagnetic anisotropies of the solutes are evaluated. Using known molecular dimensions the π electron ring currents appear, relatively to benzene as 1, to be 1.06 : 0 .19 : 0.57 : 0.37 respectively for the four heterocycles in the title.

Molecular susceptibility. The determination of molar Cotton-Mouton constants at infinite dilution in benzene or cyclohexane

Reliable measurements of the small incremental Cotton-Mouton constants encountered at low solute concentrations with solutions in which the magnetic birefringences of solute and solvent do not differ widely cannot be made with equipment at present available. Five such systems are examined in this paper. It is shown that the larger incrementa easily observable among stronger solutions can be fitted to empirical equations containing ascending powers of the concentrations and hence estimates of ΔC/w2 as w2 approaches zero become accessible. Values of ∞(mC2) obtained by this device agree reasonably with others directly drawn from much weaker solutions of the same solutes in carbon tetrachloride or cyclohexane, i.e, in media for which C1 = 0.