Enhancement Of Dipole Moment Research Articles

Dielectrometry in Supercritical Fluids. A New Approach to the Measurement of Solubility and Study of Dipole Moment Behavior of Polar Compounds

Radio frequency (rf) dielectrometry has been used to study the solubility and dipole moment behavior of polar compounds in supercritical fluid. The isothermic equilibrium solubility and dipole moments of acetonitrile, acetone, cyclopentadienyl manganese tricarbonyl (CpMn(CO)3), and copper(II) hexafluoroacetylacetonate hydrate (Cu(hfac)2·H2O) in near- and supercritical CO2 were measured at 313 K over the pressure range 5−15 MPa. It was found that dipole moment values for acetonitrile, acetone, and CpMn(CO)3 in CO2 are close to those in benzene and cyclohexane, in contrast to Cu(hfac)2·H2O, which has an enhanced dipole moment indicating strong interaction with carbon dioxide molecules.

First principles calculation of the dipole moments of small mixed Ge/Te semiconductor clusters

We investigate the structural and electronic properties of the small mixed semiconductor clusters GeTe, Ge2Te, GeTe2 and Ge2Te2 by means of first principles supercell calculations using the local density approximation and the pseudopotential plane wave method. The cluster geometry is optimized using a conjugate gradient method. For GeTe2 we confirm the linear structure (D∞h) suggested by recent experiments. For Ge2Te we obtain an equilateral triangle as the equilibrium structure. For Ge2Te2 we obtain a deformed tetrahedrom (butterfly C2v symmetry). For each of these molecules we compute the dipole moment in the equilibrium geometry and in selected geometries near to equilibrium corresponding to states higher in energy by a few tens of meV. For the equilibrium state of Ge2Te and Ge2Te2 we obtain permanent dipole moments smaller than those estimated from recent experiments at room temperature. For selected low lying excited states of these clusters, which have elongated Ge-Te bond length, we obtain enhanced dipole moments, improving the agreement with the ones estimated from experiments.

Periodic Hartree–Fock calculations on crystalline HCN

Periodic Hartree–Fock calculations on the tetragonal, high temperature, form of solid HCN are presented. Using HF/6-31G** methodology, the lattice energy per molecule is predicted to be 21.8 kJ mol−1, in good agreement with an experimental value of 19 kJ mol−1. Atoms-in-molecules decomposition of the resulting charge distribution, based on Bader’s zero-flux partitioning scheme, yields an in-crystal dipole moment of 1.734 a.u., a 38% increase over the isolated molecule. It is shown that this dipole moment enhancement is due solely to increased interatomic charge transfer, since the atomic dipoles are actually reduced by the crystal field. The intermolecular interactions in the crystal are characterized by means of the topology of the charge density; each chain is bound by relatively strong N⋅⋅⋅H hydrogen bonds, while the chains are linked by weaker C⋅⋅⋅N interactions. The effects of the crystal field on topological properties of ρ and ∇2ρ are explored, and are found to cause changes of up to 10% compared to the gas phase.

Electric dipole moment of the neutron in the Kobayashi-Maskawa model with four generations of quarks

We show that the existence of a possible fourth heavy generation of quarks gives rise to a significant enhancement of the neutron electric dipole moment in comparison with the Standard Model prediction. The smaller degree of suppression in this case is linked to the presence of the operators of dimension ≤ 6 which enter into the effective Lagrangian with coefficients proportional to the square of the top quark mass. Numerically, the enhancement is mainly associated with the chromoelectric dipole moment of the s quark which appears at the three loop level, of the order α sα w 2m sm t 2 m w 4 from the CP-odd combination of mixing angles between second, third and fourth generations. Its value is calculated explicitly in the limit of large masses of the fourth generation of quarks. The corresponding contribution to the electric dipole moment of the neutron is 5·10 −30 e·cm in the most optimistic scenarios about the values of the Kobayashi-Maskawa matrix elements. The additive renormalization of the θ-term in this model is estimated as 10 −13.

Origin of dipole moment enhancement in the formation of SiF4–NH3 dimer

The dimerization of SiF4 and NH3 is accompanied by a substantial 1.63 a.u. increase in dipole moment. Theoretical analysis of the charge distribution of the SiF4–NH3 system using the theory of atoms in molecules shows that the origin of this increase is primarily the large geometrical change which occurs within the SiF4 molecule when the dimer is formed, rather than the changes in atomic polarization or interatomic or intermolecular electron transfer. The relative displacement of the highly charged fluorine atoms of SiF4 away from NH3 upon dimer formation accounts for nearly 90% of the dipole moment enhancement. This result is in agreement with predictions made recently based on experimental results.

Head-to-tail assemblies of dipolar, piperazine-linked chromophores: synthesis, x-ray structure, and dielectric characterization

A dimer and a mixture of oligomers of acceptor-substituted anilines were prepared, either by Knoevenagel condensation of substituted cyanoacetylpiperazines with p-aminobenzaldehydes or by carbonyldiimidazole-promoted coupling of phenylpiperazines with p-aminocyanocinnamic acids. The resulting oligomeric amidopiperazines possess significantly additive molecular moments when in extended conformations and therefore are potentially valuable for the fabrication of polymer films containing electric field oriented chromophores, such as required for second-order nonlinear optics. The dimer is conformationally defined, and x-ray structural analysis of a model compound confirmed the stereochemistry and bond angles at the amide linkage. The enforced extended conformation of the dimer resulted in an enhanced dipole moment relative to the constituent monomers and raises the possibility of further enhancements in extended higher oligomers.

Microwave spectrum of the CH 3OH-NH 3 complex

Microwave spectra of CH 3OH-NH 3 and 13CH 3OH-NH 3 have been obtained using a pulsed-nozzle Fourier-transform microwave spectrometer. The spectra, which are complicated by the internal rotation of the CH 3 and NH 3 groups, exhibit five K=0 states at the ≈ 1 K rotational temperature of the expansion. Four of these are metastable, excited internal rotor states and correlate to E states of free CH 3OH or NH 3. For the two states in which the NH 3 top is in its ground internal rotor state, Δ J=1, K=0 progressions are observed and fit to linear-molecule-type frequency expressions to obtain effective spectroscopic constants. For CH 3OH-NH 3 these constants are: ( B+C)/2=3690.119(2) and 3686.114(2) MHz; eQq aa =−3.184(10) and −3.182(9) MHz; and μ a =2.854(9) and 2.956(14) D. The complexes are hydrogen bonded with an OH---N bond length of 2.02 Å. This bond length is similar to that found by Herbine and Dyke in the related HOH-NH 3 complex, 1.97 Å. Ab initio SCF calculations have also been carried out for the CH 3OH-NH 3 and HOH-NH 3 complexes in order to compare interaction-energy components and origins of the dipole moment enhancements.

On the Hartree-Fock calculation of the electron electric dipole moment enhancement factor of the thallium atom

A perturbation theory expansion of the relativistic Hartree-Fock calculation of the electron electric dipole moment enhancement in thallium is considered. The RPAE result appears to be highly overestimated because of an overestimation of the T-odd exchange polarisation in the self-consistent calculation. The correlations calculated in present work reduce this result by 70%.

Charge distribution and proton transfer in hydrogen bonded complexes

Some problems related to the dipole moment enhancement (Δμ) caused by hydrogen bond formation between neutral proton donor and acceptor molecules are discussed. Special attention is paid to the relation between Δμ and the degree of proton transfer (PT). New results are presented with respect to the effects of temperature and solvent on the dipole moments of strongly hydrogen bonded systems. These effects can be entirely related to a shift of the proton transfer equilibrium. It was shown that, in the solid state, the dipole moment changes can be investigated using the nuclear quadrupole resonance (NQR) frequencies of quadrupole nuclei on the outside of the hydrogen bridge. The plot of NQR frequency versus the donor-acceptor properties of interacting components can be formally described by means of the PT equilibrium, although the shapes of the potential energy and free energy surfaces are different from those in solution. New crystallographic data concerning the complexes of phenols and car☐ylic acids with amines indicate a single potential energy minimum which moves from the donor to the acceptor molecule. The properties of hydrogen bonds at the inversion (critical) region, where the proton occupies (statistically) a position close to the centre of the bridge, are discussed. In solution a PT equilibrium appears, while in the solid state an asymmetric single flat minimum is postulated.

Hexapole focusing and orientation of HCl and HBr via their hydrogen-bonded complexes with benzene

Polar diatomic molecules such as the hydrogen halides (HX) cannot be readily oriented by conventional electrostatic field techniques. However, by forming the 1:1 hydrogen-bonded complex with benzene (a floppy C 6v symmetric top) the HX becomes orientable via the electric hexapole focusing method. Oriented-molecule beams of C 6H 6-HCl and C 6H 6-HBr have been prepared and studied. From the threshold focusing voltage their electric dipole moments have been estimated: 1.6 ± 0.1 and 1.2 ± 0.1 D for C 6H 6-HCl and -HBr, respectively. These results confirm the substantial dipole moment enhancement of HX upon hydrogen bonding, measured accurately for the C 6H 6-HF complex by Klemperer and co-workers (1983).

Solvent Effect Upon Dipole Moment and Proton Transfer Equilibrium in Ortho Mannich Bases

AbstractThe dipole moments of ortho Mannich bases containing intramolecular OH…N hydrogen bonds were determined in solvents of various electric permittivity. The dipole moment of 2‐(N,N‐diethylaminomethyl)‐3,4,6‐trichlorophenol does not depend on the solvent polarity and simultaneously no contribution of the proton transfer form was detected in ultraviolet‐visible spectra. The dipole moments of 2‐(N,N‐diethylaminomethyl)‐3,4,5,6‐tetrachlorophenol and 2‐(N,N‐diethylaminomethyl)‐4‐nitronaphtol‐1 increase distinctly with the solvent polarity. The dipole moment enhancement can be quantitatively correlated with the displacement of the OH…N ⇄ O−…H‐N+ equilibrium towards the more polar proton transfer form. The solvent influence on the free energy of the proton transfer process, ΔGPT is discussed in terms of various effects.

Two, three, and four body interactions in model water interactions

Dimer energy surfaces for three models of the water-water interaction are examined and compared with high level ab initio SCF calculations for two important sections. All three models studied (ST2, MCY, and PE(Q) show significant differences which would be expected to be important in full liquid state simulation; the inclusion of an additional dipole-octupole term in PE appears sufficient to reproduce the energy-angle variations shown in the SCF calculations. ST2 distinguishes too strongly between the lone pairs on the acceptor water molecule, while MCY shows little sign at all of lone pair separation. All three models disagree with the rotational barrier heights given by the SCF calculations; these differences we would expect to have structural consequences in a room temperature liquid ensemble. Although there are insufficient experimental and numerical data available to fully test the three-body (and higher) interactions of the PE model, good agreement is obtained with experimental enhanced dipole moments in Ice Ih and the water dimer and with ab initio trimer energy calculations. Within the PE framework, four body and higher terms are shown to be negligible, as predicted on theoretical grounds by Murrell et al. [37].

Effect of solvents on dielectric, spectroscopic and thermodynamic manifestations of intermolecular interactions. Iodine complexes of pyridine and picoline

Dipole moments of pyridine and γ-picoline complexes with I2 in a number of nonpolar and weakly polar solvents were determined and the contributions of the dative structure FN in the ground state were estimated. The results are consistent with those calculated from the force constants of stretching vibrations v(N-l) and v (I-I). A good correlation of FN was found with respect to the solvent shift of the transition energy {ie355-1} in the I2 molecule bounded to amines and also to empirical parameters of solvent activities like rate constants of the Menshutkin reaction or the Dimroth-Reichardt parameter. No correlation exists between the solvent induced enhancement of the dipole moment and dielectric permittivity in terms of the Onsager reaction field theory.

The nature of hydrogen bonding in the NN–HF, OC–HF, and HCN–HF complexes

The nature of hydrogen bonding in the complexes NN–HF and OC–HF, as revealed from detailed ab initio electronic structure calculations, is unlike the bonding in the isoelectronic HCN–HF complex. The strong dipole–dipole attraction in HCN–HF is absent in the other two complexes. Competing effects that are possible in all hydrogen bonds are unmasked in NN–HF and OC–HF. Calculations have been performed with a number of large basis sets, extensive treatment of electron correlation, energetic partitioning, and evaluation of molecular properties. The potential energy surfaces that were generated demonstrate the linearity of the equilibrium structures, and show roughly comparable flexibility for bending, thus refining somewhat the experimentally inferred picture. In NN–HF and OC–HF, less than one-half of the hydrogen bond strength of each is due to just the interaction of the unrelaxed charge distributions of the monomers; while polarization of monomer electron distributions accounts for most of the remaining attraction. There is consequently a substantial electric dipole moment enhancement. The total correlation effect is responsible for about one-third of the well depth in NN–HF and OC–HF. Charge transfer is unimportant in all three complexes.

Improved procedure for analysis of electron density redistribution in molecular complexes

An improved method for theoretical determination of the charge redistribution, i.e., the intramolecular charge shifts, intermolecular charge transfer, and dipole moment enhancement upon complexation, is proposed. This approach consists of counterpoise correction of the basis set superposition error on calculated electron density redistribution in molecular complexes. Ab initio LCAO MO SCF calculations for HF⋅⋅⋅HNH2, H2O⋅⋅⋅HOH, H2O⋅⋅⋅HF, H3N⋅⋅⋅HF, H3N⋅⋅⋅LiF, CO⋅⋅⋅HCN, H2S⋅⋅⋅OCHNH2, H2NHCO⋅⋅⋅HSH, [Mg⋅⋅⋅OH]+ [HO⋅⋅⋅HOH]−, [Be(OH)(NH3)2]+ molecular complexes in different basis set have been performed leading to more consistent results in contrast to sometimes largely overestimated uncorrected values reported previously. In addition, the charge redistribution upon complex formation has been analyzed for some dimers in terms of atomic multipole expansion of electron density and difference molecular electrostatic potentials.

Study on the i.r. band intensities of cyclopropane

The i.r. absorption intensities of cyclopropane-h 6 and -d 6 were measured in the gas phase using the pressure broadening technique. The obtained band intensities were analysed in order to determine the intensity parameter (∂ p/∂ S j ) with the help of information from the Coriolis interaction and CNDO/2 calculation. It has proved that the Coriolis interaction can offer important information even for a couple of bands which are mutually removed far away. In case of C 3H 6, despite 400 cm −1 distance between the ν 9 and ν 10 bands, the product ζ z 9 a,10 b (∂ p x/∂ Q 9 a )(∂ p y/∂ Q 10 b) has been determined as positive. In this way the sign of (∂ p/∂ Q i ) has been clearly decided for cyclopropane, and consequently the value of (∂ p/∂ S j ) has been definitely determined. Further, by investigating the present results with those previously obtained, for many other related molecules, the following general rule has been found about the relationship between the sense of displacement vector of hydrogen atom group and the enhanced dipole moment vector induced thereby. Namely, the directions of these two vectors are opposite for the stretching vibrational modes and the same for almost all deformation vibrational modes of hydrogen atoms.

CNDO/2 Study on molecular complexes of aliphatic amines with HF and F2

Abstract Properties of molecular complexes formed between aliphatic amines with HF and F2, respectively, have been evaluated by the CNDO/2 method. In the amineHF hydrogen-bonded complexes the calculated properties (binding energy, amount of charge transferred, enhancement of dipole moment) are fairly constant in the series of systems studied. In the amineF2 charge transfer complexes the binding energy decreases and the amount of charge transferred slightly increases with the lowering of the amine's ionization potential. The results obtained are discussed in relation to the electronic structure of the complexes formed.

Hydrogen Bonding Systems Containing Hydrogen Fluoride. III. Infrared Frequency Shifts and CNDO/2 Calculations on HF-Carbonyl Compound Complexes

Abstract CNDO/2 calculations were carried out for the hydrogen bonded complexes between hydrogen fluoride (HF) and a series of organic compounds having a carbonyl group as a proton acceptor. Infrared spectral measurements were also made to obtain the frequency shifts of H–F stretching vibration, ΔνHF, for the same complexes in dilute carbon tetrachloride solution. Optimum geometry was obtained on the assumption of planar complex. For all the carbonyl compounds used, the interatomic angles, ∠C–O···H, were 120°–123° for the most stable conformation. The changes in the distance between H atom and F atom, ΔRHF, were in good correlation with ΔνHF obtained from IR spectra. Calculated hydrogen bond energies were also in good correlation with ΔνHF, though their absolute values were somewhat larger than those derived from experimental observations. This indicates that the CNDO/2 calculations give relatively correct enthalpy values for the hydrogen bond complexes of a given donor with a series of molecules having a common acceptor group. Other correlations of ΔνHF with properties expected to change with the hydrogen bond formation were also confirmed. These include the energies of each bond obtained by the partitioning of the total energy and the force constant of H–F bond. The electron population on the oxygen atom and other atoms participating in the hydrogen bond formation, the charge transfer, ionization potentials and dipole moment enhancements were also calculated and discussed in terms of the measure of hydrogen bond strength.

Dipole moment enhancement on formation of a hydrogen-bonded complex. Demonstration and measurement of the effect for HCN…HF by microwave spectroscopy

The microwave spectrum of the heterodimer HCN…HF is reported, the collinearity of the nuclei established, and r 0(N…F)=2.796 Å obtained. From the Stark effect, μ 0(HCN…HF)=5.59 ± 0.02 D which indicates an enhancement of 0.78 D over the vector sum of the monomer values.

Charge transfer theory and vibrational properties of the hydrogen bond

An extension of Mulliken's charge transfer theory leads to the following correlations: the change in the transition moment of the X—H stretching vibration with the enhancement of dipole moment, and the displacement of the X—H stretching frequency with the ionization of donors. Experimental data for a number of hydrogen-bonded complexes are in accord with these predictions.