A dipole moment study of annular tautomerism in 5-p-tolyltetrazole

The electric dipole moment of 5-(p-tolyl)tetrazole in dioxane at 30.0° (4.99 D) suggests that the compound is a mixture of the 1H-tautomer (60 ± 10%) and the 2H-tautomer (40 ± 10%) in this medium. This determination was made by taking μ (2H) as μ (2Me) = 2.41 D in benzene, and by taking μ (1H) as μ (1Me) = 6.03 D in benzene with due allowance being made for the presence of interannular conjugation in the 1H-tautomer but not in the 1-methyl isomer. The dipole moments of 1-methyl-5-(p-tolyl)tetrazole and 2-methyl-5-(p-tolyl)tetrazole were also measured in dioxane; that of 1,5-trimethylenetetrazole was measured in benzene. Comparison with relevant data for unsubstituted tetrazole has also been made.     

A dipole moment study of the structures of some ketene acetals

The dipole moments of several acyclic and cyclic ketene acetals have been determined in benzene solution at 293 K using the Halverstadt-Kumler method. For ketene dialkyl acetals (alkyl = Me, Et) the results point to a predominance of the s-cis,s-trans retamer, which disagrees with the conclusions drawn previously from ¹³C NMR chemical shift data, i.e. the s-cis,s-cis form is the more stable species. In the case of 2-methoxyfuran, the dipole moment measurements confirm the previous findings based on the ¹³C NMR spectra, viz the s-cis form is the predominating rotamer. The dipole moments and structures of some other ketene acetals are also discussed.     

A dipole moment study of n-trimethyl-ammoniobenzamidates and n-benzoyliminodimethylsulphur(iv)

Analysis of the dipole moments of N-trimethylammoniobenzamidates Me₃N⁺-N^?COC₆H₄X, with X = H, p-F, p-Cl or p-NO₂, and of N-aroyliminodimethylsulphur(IV) Me₂SNCOC₆H₄X (X = H and p-NO₂) shows that, as solutes, these compounds exist in the syn conformation. Models are proposed for N-trimethylammonio-orthochloroben-zamidate and N-orthocyanobenzoyliminodimethylsulphur(IV). The (Me₃N⁺-N^t-) and (SN) dipole moments, and the (N-CO) and (SN-CO) mesomeric moments, are derived and discussed.     

Water dimer dipole moment

The peculiar properties of the behavior of effective polarizability of water molecules in its saturated vapor are discussed on the basis of the experimental data on the static dielectric constant. It is taken into account that in the region 273 K < T < 485 K there is a mixture of monomers and dimers in the water vapor. The comparison of the theoretical and experimental expressions for the effective polarizability shows that the dipole moment of water dimer is connected with the dipole moment of monomer via relation: d _D = √2d _m. The relative value of the irreducible pair contributions to the polarizability of the dimer is determined.     

A CASPT2 study of the dipole moment surfaces of hydrogen sulphide molecule

The ability of the CASPT2 method to yield accurate H₂S dipole moment surfaces that could be further used for conclusive predictions about rovibrational calculations, has been evaluated using ANO-L basis set. The optimised geometry, permanent dipole moment, linearity barrier as well as general features of the μ_x and μ_z dipole moment components in the vicinity of the equilibrium configuration agree favourably with available empirical determination and with recent accurate ab initio calculations. Dipole moment functions behaviour is also well reproduced for those geometrical configurations which are far from equilibrium in dissociation path. Computational technical aspects are discussed.     

Electric dipole moment of BrCl

The electric dipole moment of the BrCl molecule has been determined by a study of the Stark effect on nine hyperfine components of the J = 1 ← 0 rotational transition lying at 9 GHz. A direct diagonalisation procedure of the energy matrix of the total hamiltonian has been used and the electric dipole moment derived for the ground vibrational state of BrCl is |μ_o| = 0.519 ± 0.004 D.     

A dipole moment study of the conformational properties of diaryl diselenides and related compounds

The electric dipole moments of the diaryl diselenides (RC₆H₄)₂Se₂ (R  H, 4-F, 4-Br, 4-CH₃, 3-F) were measured in benzene solution at 25 and 45°C. The conformations of these compounds were deduced by matching experimental moments with values calculated for a variety of possible conformations. In the dissolved state the diselenides exist at 25°C in fixed “skew” conformations characterized by dihedral angles of 75–106° between the CSeSe planes, corresponding to the conformational energy minima. At 45°C oscillations about the SeSe bonds are excited in the diphenyl and bis(4-methylphenyl) diselenides, whereas the 4-bromophenyl derivative exhibits free rotation. The fluoro compounds have temperature-independent dipole moments, suggesting “rigid conformations” with dihedral angles of 106° (4-F) and 74.4° (3-F). An analysis of the dipole moments at 25 and 45°C obtained for the compounds (RC₆H₄)₂X₂ (R  H, 3-F, 4-F, 4-Br, 4-CH₃; X  S, Se, Te) showed that the conformational properties of these derivatives change on passing from X  S to X  Te. The observed variations are explicable in terms of a decreasing repulsion between the lone electron pairs of the chalcogen atoms on going from the disulfides to the ditellurides and a concomitant reduction of the energy barrier to rotations about the XX bonds.     

Theoretical study of the dipole moment of oxygen monofluoride (OF)

Theoretical X²II potentials and dipole moment functions for OF are presented at the CASSCF, externally contracted Cl, and MRCI(SD) levels using DZP and extended gaussian basis sets. The best theoretical results (with experiment in parentheses) are μ_ν =0 = ?0.0089 (?0.0043) and μ_ν=1 = ?0.0318 (?0.0267) D, where the minus sign implies O⁺F^?.     

Microwave spectrum and dipole moment of norbornane

The microwave spectrum of norbornane has been studied in the 26–40 GHz region. The rotational constantsA = 3694.246 MHz B = 3212.566 MHz, C = 2774.813 MHz and the dipole moment μ = 0.091(8) D have been determined. These values are compared with electron diffraction data.     

Permanent electric dipole moment of molybdenum carbide

High resolution optical spectroscopy has been used to study a molecular beam of molybdenum monocarbide (MoC). The Stark effect of the R(e)(0) and Q(fe)(1) branch features of the [18.6] (3)Pi(1)-X (3)Sigma(-)(0,0) band system of (98)MoC were analyzed to determine the permanent electric dipole moments mu(e) of 2.68(2) and 6.07(18) D for the [18.6] (3)Pi(1)(nu=0) and X (3)Sigma(-)(nu=0) states, respectively. The dipole moments are compared with the experimental value for ruthenium monocarbide [T. C. Steimle et al., J. Chem. Phys. 118, 2620 (2003)] and with theoretical predictions. A molecular orbital correlation diagram is used to interpret the observed and predicted trends of ground state mu(e) values for the 4d-metal monocarbides series.     

A stochastic model for the molecular dipole moment correlation function

An nth order truncation of the continued fraction representation of the molecular dipole moment correlation function is introduced from the free rotation representation and an interaction process which is supposed to be governed by a Poisson distribution. We can then derive a general expression for the correlation function, related both to the natural distribution of angular velocities and the successive time derivatives of the mean square torque due to molecular interactions. Some numerical results and comparisons with experiments are given in the second order truncation case.     

Tautomerism in arylazonaphthols by dipole moment analysis

The azo-hydrazone equilibrium in some arylazonaphthols has been studied by dipole moment measurements and HMO calculations. Results show that in 1,4-derivatives comparable amounts of both forms are present. The 1,2-derivatives appear to be essentially azo-compounds, but an overestimate of azo proportion cannot be excluded.     

Exchange-hole dipole moment and the dispersion interaction

A simple model is presented in which the instantaneous dipole moment of the exchange hole is used to generate a dispersion interaction between nonoverlapping systems. The model is easy to implement, requiring no electron correlation (in the usual sense) or time dependence, and has been tested on various atomic and molecular pairs. The resulting C6 dispersion coefficients are remarkably accurate.     

The dipole moment, polarizabilities, and first hyperpolarizabilities of HArF. A computational and comparative study

The electronic and vibrational contributions to the dipole moment, polarizabilities, and first hyperpolarizabilities of HArF are reported. These have been computed by using a series of systematically built basis sets and a hierarchy of computational methods. HArF has a very large first hyperpolarizability along the z axis. This has been rationalized by invoking the difference in the electronic structure between the ground and the first excited state. The argon fluorohydride has been recently derived and characterized. The present study provides complementary data for the understanding of the electronic structure of this interesting argon derivative.     

Very-long-range static dipole moment of two coupled systems

The expression for the very-long-range dipole moment of a pair of non-identical centrosymmetric systems (varying as R^?8) is obtained. Our expression is given in terms of polarisabilities and hyperpolarisabilities of the two systems and is compared with two previous results.     

Microwave spectrum and dipole moment of 1,2,3,4-tetra-fluorobenzene

The microwave spectrum of the ground state of 1,2,3,4-tetrafluorobenzene has been measured in the range 7 to 25 GHz. A possible structure of the molecule is discussed. The rotational constants obtained are (in MHz): A = 2090.711 ± 0.012, B = 1196.257 ± 0.014, C = 760.880 ± 0.005. The observed inertial defect, Δ = 0.010 amu Ų, confirms the planar structure. A dipole moment of 2.42 ± 0.05 Debye was determined.     

Nonadiabatic contribution to the dipole moment of HCl

Nonadiabatic corrections to the dipole moments of HCl and DCl are calculated. Kaiser's deduction that the effect of the breakdown of the Born-Oppenheimer approximation is to reduce the dipole of DCl relative to HCl by about 10^?3 D is shown to be realistic.     

Electric dipole moment of the diatomic AgBr molecule

Stark effect measurements on hyperfine components of the J = 3 – 2 rotational transition of ¹⁰⁷ Ag ⁷⁹ Br and ¹⁰⁹ Ag⁷⁹ Br at 11.5 GHz were carried out. The electric dipole moment derived for AgBr in its ground electronic and vibrational state is |μ_o| = 5.620 ± 0.030 D.     

Microwave spectrum and dipole moment of glycolic acid

More than 200 rotational transitions of glycolic acid (CH₂OHCOOH) have been assigned in the frequency range 18–40 GHz. Rotational constants and centrifugal distortion constants for the ground state and two vibrationally excited states were deduced. From Stark splittings the dipole moment was determined: μ_a = 1.913(5), μ_b = 0.995(14) and μ_total = 2.156(9) D.