The effect of molecular polarity on nem/catic phase stability in 12-vertex carboranes

Weakly polar–polar isosteric pairs of 12-vertex p-carborane [closo-1,12-C₂B₁₀H₁₂] (1[12]) and monocarbaborate [closo-1-CB₁₁H₁₂]^? (2[12]) nematic liquid crystals, in which the difference in the calculated molecular dipole moment is 11.3 D, were synthesised, and the effect of the dipole moment on nematic phase stability was investigated. The trend observed for the 12-vertex series ([12]) was identical to that of the previously investigated 10-vertex series ([10]) containing [closo-1,10-C₂B₈H₁₀] (1[10]) and [closo-1-CB₉H₁₀]^? (2[10]): the uniform increase in the molecular dipole moment in the pairs of mesogens does not correspond to a uniform change in the clearing temperature, T_NI. This demonstrates the role of a remote substituent in modulating the intermolecular dipole–dipole interactions. The magnitude of such interactions was calculated (using density functional theory methods) for a pair of polar (2[12]d–2[12]d) and an analogous pair of weakly polar (1[12]d–1[12]d) molecules. All results for the 12-vertex series ([12]) were analysed relative to the 10-vertex analogues ([10]).     

Investigations on Binary Mixtures of Propan-2-ol with Methyl Benzoate and Ethyl Benzoate

The molecular interactions between the polar systems propan-2-ol with alkyl benzoates (methyl benzoate and ethyl benzoate), for various mole fractions and different temperatures, were studied by determining the dielectric permittivity using a LF impedance analyzer and Abbe’s refractometer in the static and optical frequency regions, respectively. The effective Kirkwood correlation factor, corrective Kirkwood correlation factor, dipole moment, excess dipole moment, and excess Helmholtz free energy were calculated using the experimental data. Hamiltonian quantum mechanical calculations (ab initio and semiempirical) were performed using PC Spartan and Argus lab Modeling software for both pure and equimolar binary systems of propan-2-ol with alkyl benzoates.     

Electrostatic bonding models: A test on group 1 and 2 metal complexes with H2O,NH3, H2S,PH3, and related ligands

Electrostatic models frequently proposed to describe ion–molecule interactions have been tested on the adducts formed by Group 1 and 2 cations with H₂O, NH₃, H₂S, PH₃, their methyl analogs, and their anions. The results from the model calculations were compared with all-electron calculations (geometry optimized, MP2, TZP basis sets) carried out on adducts formed with Li⁺, Na⁺, K⁺, Ca²⁺, and Mg²⁺. The electrostatic potential model was utilized in two ways: The attraction of the point charge was calculated with and without relaxation of the ligand. A third model allowed relaxation of the ligand but treated the cation as a frozen core. The final model was the crude point charge/point dipole approximation. At long range, the models satisfactorily track the effects on energy of gross changes in the ion–ligand interaction (monovalent versus divalent ions, neutral ligands versus anions, parent ligands versus methyl derivatives), but correlation at close range is poor, especially for binding by divalent cations. The hypothesis that the calculated strength of cation–dipole binding is dependent on calculated dipole moment could not be verified. © 1995 by John Wiley & Sons, Inc.     

Dipole moment and self-association of cyclohexylsulfamic acid in 1,4-dioxane solution at 298.15?K

Abstract  

The density, refractive index, and electrical permittivity of cyclohexylsulfamic acid in 1,4-dioxane solutions were measured at 298.15 K. The limiting apparent specific volume, refraction, and polarization were calculated from the experimental data. The electrical dipole moment of cyclohexylsulfamic acid was estimated using the Debye, Onsager, and Kirkwood equations. The dipole association of cyclohexylsulfamic acid was treated with the assumption that the dipole moment of dimeric species is zero. The dimerization constant and dipole moment of monomeric species were evaluated.     

The effect of intermolecular actions on the nematic phase range of tolane-liquid crystals

An approach to understand the effect of intermolecular actions on the nematic stability, a series of tolane compounds nH containing intermolecular π–π stacking, dipole–dipole and hydrogen bond interactions, are developed and investigated. Their mesophase behaviour were measured by differential scanning calorimetry (DSC) and polarising optical microscopy (POM), the results show that carboxylic acids nH exhibit high melting points and narrow nematic phase intervals, which are attributed to the too strong intermolecular actions. By disrupting the intermolecular hydrogen bond, their corresponding methyl esters nC have been designed and synthesised. It is interesting to note that these compounds exhibit broad nematic mesophase intervals and low melting points. The above results demonstrate that the interruption of intermolecular actions is an effective way to improve the nematic stability. In addition, the effects of the terminal alkyl chains and the terminal polar groups on the nematic stability were also discussed. Finally, DFT calculations of molecular conformation and dipole moment were conducted to better understanding of the molecular structure–mesomorphic property relationship.     

Synthesis and properties of hydroxy tail-terminated cyanobiphenyl liquid crystals

Two series of new hydroxy tail-terminated cyanobiphenyl compounds are described. The 4′-ω-hydroxyalkynyl-4-cyanobiphenyl compounds (1a–1g) were synthesised as the key intermediates to the 4′-?ω-hydroxyalkyl-4-cyanobiphenyl compounds (2a–2g) obtained upon reduction of the acetylenes. Many of these ω-hydroxyalkynyl and ω-hydroxyalkyl cyanobiphenyl compounds exhibit nematic mesophases and they also serve as precursors for the synthesis of other interesting materials. Using density functional theory, we calculate the dipole moment of all relevant ω-hydroxyalkynyl and ω-hydroxyalkyl cyanobiphenyl compounds and find a correlation between the calculated dipole moments and measured crystalline to nematic or isotropic liquid transition temperatures.     

Interaction potentials and free energies for ferroelectric liquid crystals in the model of polar non-uniaxial molecules

Abstract

The possible forms of the model interaction potentials are proposed for rigid polar non-uniaxial molecules with the molecular dipole moment making an arbitrary angle with the molecule's long axis. The molecule orientation is described by the direction of two molecular axes: its dipole moment and the long axis. The intermolecular potentials dependent on both molecular axes orientations are considered. The simple model interaction potentials between chiral molecules are used. It is shown that the form of the interaction potential determines the set of the relevant order parameters of the system. The free energy is calculated in the Landau expansion form in terms of the relevant order parameters.     

Molecular interaction studies in hydrogen bonded polar binary mixtures

The molecular interactions between the polar systems of propan-1-ol (1PN) with alkyl benzoates (methyl benzoate and ethyl benzoate) for various mole fractions at different temperatures are studied by determining the dielectric permittivity in radio, microwave and optic frequency regions, respectively. Dipole moment, excess dipole moment, excess Helmholtz free energy, excess permittivity, relaxation time, excess inverse relaxation time and excess thermodynamical values are calculated using experimental data. Hamiltonian quantum mechanical calculations are performed on both pure and equimolar binary systems of 1PN with alkyl benzoates for the measurement of dipole moment from the ab initio Hartree–Fock and density functional theory (B3LYP) methods with 6-31?+?G* and 6-311?+?G** basis sets using Spartan 08 modelling software and these theoretical values are in good agreement with the experimental values.     

Spectral and Quantum Mechanical Characterization of 3-(2-Benzothiazolyl)-7-(Diethylamino) Coumarin (Coumarin 6) in Binary Solution

ABSTRACT

Absorption and fluorescence spectra of 3-(2-benzothiazolyl)-7-(diethylamino) coumarin in various solvents were recorded to characterize intermolecular interactions. The contributions of each interaction to the total spectral shifts were estimated. The properties of coumarin 6 were calculated using density function theory with the hybrid functional B3LYP level theory combined with 6-311?+?G basis set. The excited state dipole moment was calculated from the variation of spectral shifts in absorption and fluorescence with solvent permittivity and refractive index using the Lippert–Mataga, Bakhshiev, and Kawski–Chamma–Viallet equations.     

Spontaneous Polarization of Thin Water Films in Nonwettable Capillaries by the Data of Numerical Experiment

Abstract–Water films in the flat capillaries with ideal walls were simulated by molecular dynamics method. The profiles of local density and distribution functions of the dipole moment orientations, the directions of valence and H-H bonds were obtained. Profiles of local electric field and electric potential were calculated. Potential jumps at the water–vapor interface were estimated.     

Chair and boat conformations in the a ring of 4,4-dimethyl-3-keto steroids

The conformation of the A ring in 4.4-dimethylandrostan-3-ones in solution was determined to be a chair from the coupling observed in the ¹H NMR spectrum. The dipole moment of the 3,17-dione agrees with the dipole moment calculated for the proposed conformation. Force field calculations predict that in 4,4-dimethylandrost-5-en-3-ones the A ring prefers a non-chair conformation, in agreement with the dipole moment determined for the Δ⁵- 3.17-dione and NMR results.     

Hybrid-Density Functional Theory Study and Natural Bond Orbital Interpretation of the Conformational Behavior of 1,3-Dioxanyl, 1,3-Dithianyl,and 1,3-Diselenanyl Carbanions

Abstract

The effective factors on the conformational properties of 1,3-dioxanyl (1), -dithianyl (2), and -diselenanyl (3) carbanions have been investigated by means of the hybrid-density functional theory (DFT) (B3LYP/6-311+G**)-based method and natural bond orbital (NBO) interpretation. The results obtained showed that the axial conformation (i.e., the axial H atom attached to C₂) of carbanion 1 is more stable than its equatorial conformation. Contrary to the carbanion 1, the equatorial conformations of carbanions 2 and 3 are more stable than their corresponding axial conformations. The instability of the axial conformations of carbanions 1–3 increases from carbanion 1 to carbanion 2 but decreases from carbanion 2 to carbanion 3. The NBO analysis showed that the anomeric effect (AE) associated with the electron delocalization increases from carbanion 1 to carbanion 2, but decreases from carbanion 2 to carbanion 3. The calculated total dipole moment values of the axial conformations of carbanions 1–3 are greater than those of their corresponding equatorial conformations, but the calculated total dipole moment difference values between the axial and equatorial conformations decreases from carbanion 1 to carbanion 3. Consequently, the AE associated with the electron delocalization, but not the total dipole moment changes (i.e., Δμ_ax–eq), thus explaining the total energy differences between the axial and equatorial conformations of carbanions 1–3. The correlations between the AE, dipole moments, ΔG_ax–eq, structural parameters, and conformational behaviors of carbanions 1–3 have been investigated.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

Microwave spectrum,centrifugal perturbation,dipole moment,and conformation of 5-methyl-1,3-dioxane

The microwave spectrum of 5-methyl-1,3-dioxane was studied in the frequency range 12–35 GHz. The a and c type rotation transitions with J≤30 were identified. The rotational constants A = 4658.5244(33) MHz, B = 2383.3930(12) MHz, and C = 1724.28907(88) MHz and the quartic constants of the centrifugal distortion of the molecule in the ground vibrational state were determined. The components of the dipole moment were found, μ _a = 1.76 ± 0.01 D and μ _c = 1.10 ± 0.01 D; the net dipole moment of the molecule is μ = 2.08 ± 0.01 D. 5-Methyl-1,3-dioxane was calculated by the B3PW91/aug-cc-pVDZ density functional theory method. The calculated data are compared with the experimental data. The most stable conformation is the chair conformation with an equatorial orientation of the methyl group.     

Dipole Moment Studies of n-butanol,i-butanol and t-butanol with Chlorobenzene Complexes

Abstract

The dipole moments of H-bonded complexes of n-butanol, i-butanol and t-butanol with chlorobenzene in benzene were investigated from dielectric measurements at 455 kHz and at temperature 303.16 K. The dipole moment of the complex (μab), interaction dipole moment (Δμ) and induced polarization (Pab) for thermodynamically most favoured geometry of 1:1 complexes in these systems were determined. The results shows that the complexation is due to charge redistribution effect in all cases studied and the tendency of complex formation is maximum in n-butanol system.     

Theoretical Infrared Radiative Lifetimes for CO a3∏

INDO self-consistent-field method was employed to calculate the potential energy and dipole moment functions for the excited a³∏ state of CO. Vibrationally averaged dipole moments and infrared radiative lifetimes were then obtained from the dipole moment function and vibrational wave functions generated by solving numerically the Schrödinger equation for nuclear motions. The calculated dipole moment is 1.468 (expt'I 1.375 D) for ν=0, and decreases with increasing ν, as found experimentally. Calculated infrared radiative lifetimes, with experimental results in parentheses, are 13.5 (17.3, 19.0±5.9), 7.3 (7.8, 13.1±2.9), and 5.0 (4.7, 5.6±1.0) msec, respectively, for ν=1, 2, and 3. The polarity of calculated dipole moment is C⁺O^?, differing from that for the ground X¹∑⁺ state. The origin of this difference is found to be due to the delocalization of the 5a orbital in the a³∏ state.     

Solvent effect on tautomeric equilibria and dipole moments of some alpha substituted benzoylacetanilides

Based on dipole moment measurements, a study was made of the keto-enol equilibria of five alpha substituted benzoylacetanilide derivatives in two non-polar and one polar solvents at 30°C. The enol mole fractions of the compounds investigated were determined by analysis of their ultraviolet spectra. The same type of study was extended to salicylanilide for its resemblance to the enol tautomer of these compounds. A deduction of the most probable configurations of the keto and enol forms was tentatively made through a comparison between the dipole moments of some suggested configurations for these forms of benzoylacetanilide and those measured in benzene for the alpha methyl benzoylacetanilide and salicylanilide, respectively. These inferred configurations were used to calculate the dipole moments of both tautomers of the other compounds, and consequently, the dipole moment values of their tautomeric mixtures in dioxane and chloroform. A comparison between the dipole moment values of their tautomeric mixtures in dioxane and chloroform. A comparison between the dipole moment values calculated in this way and those measured indicated a solute-solvent interaction with dioxane, which chloroform behaved as a non-interacting solvent.     

Finite-field method calculations. IV. Higher-order moments,dipole moment gradients,polarisability gradients and field-induced shifts in molecular properties: Application to N2, CO,CN−, HCN and HNC

In this paper, theoretical methods developed in III are applied in calculating polarisabilities, polarisability gradients and field-induced shifts, by the finite-field method. Values of dipole moment gradients and higher-order moments, calculated from the unperturbed wavefunctions, are also reported. Results for N₂, CO, CN^?, HCN and HNC have been obtained at the SCF level; some CI results for the N₂ polarisability components and moments and for the dipole moment gradients of HCN are also given. The calculated polarisability gradients and dipole moment gradients have been used to estimate the Raman scattering intensities and depolarisation ratios and the IR absorption intensities. Model calculations of field-induced shifts in bond length, vibrational levels, spectroscopic constants, force constants and dipole moment gradient are reported for N₂ and CO.The discrepancy between the SCF and experimental bond dipole moment gradients for HCN, previously noted in the literature, has been re-examined and resolved by our CI results.     

Studies in the chemistry of erythrina alkaloid derivatives—III : Two isomers of 2,3,4,4a,5,6,7,7a,8,9,10,11-dodecahydro-2,10-dioxo-1H-benzo[d]naphthalene

Diketone 2,3,4,4a,5,6,7,7a,8,9,10,11-dodecahydro-2,10-dioxo-1H-benzo[d]-naphthalene prepared by annulation of N-(1-cyclohexenyl)pyrrolidine with vinyl methyl ketone, was found to consist of two stereoisomers. Theoretical dipole moments of these were calculated, and their structures were shown by moment dipole measurements to be cis A/B, cis A/C and trans A/B, cis A/C, respectively. The isomer trans A/B, cis A/B was converted into trans A/B, cis A/C dodecahydro-1H-benzo[d]naphthalene by the Wolff-Kishner reduction.     

Apparent Specific Polarization and Dipole Moment of Some Poly(oxyethylene) Glycols in 1,4-Dioxane and Benzene Solutions at 298.15 K

Summary. The electrical permittivity of 1,4-dioxane and benzene solutions of some poly(oxyethylene) glycols up to the average molecular weight of 1590 were measured at 298.15 K. From the experimental data the limiting apparent specific polarization and partial molar polarization were calculated. The electrical dipole moment of the investigated solutes was estimated according to the Debye, Onsager, and Kirkwood theoretical approaches. The calculated dipole moments increase linearly with the square root of the number of monomeric units. The group dipole moment of the polar monomeric unit was calculated from the corresponding limiting partial molar volume, the refraction and polarization of the solute. The factor g, which takes into account the degree of flexibility of the chain, was estimated and found to be greater than 0.92, which means that the lower members of the poly(oxyethylene) glycols possess almost free rotation within the chain backbone of polymer.     

Apparent Specific Polarization and Dipole Moment of Some Poly(oxyethylene) Glycols in 1,4-Dioxane and Benzene Solutions at 298.15?K

The electrical permittivity of 1,4-dioxane and benzene solutions of some poly(oxyethylene) glycols up to the average molecular weight of 1590 were measured at 298.15 K. From the experimental data the limiting apparent specific polarization and partial molar polarization were calculated. The electrical dipole moment of the investigated solutes was estimated according to the Debye, Onsager, and Kirkwood theoretical approaches. The calculated dipole moments increase linearly with the square root of the number of monomeric units. The group dipole moment of the polar monomeric unit was calculated from the corresponding limiting partial molar volume, the refraction and polarization of the solute. The factor g, which takes into account the degree of flexibility of the chain, was estimated and found to be greater than 0.92, which means that the lower members of the poly(oxyethylene) glycols possess almost free rotation within the chain backbone of polymer.