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Dielectric relaxation measurements have been performed on nitropentachlorobenzene and tetrachlorometaxylene in the frequency range 100 Hz to 1 MHz and in the temperature range 152–400 K. In addition, scanning calorimetric measurements have been carried out. From the results obtained, a possible mechanism has been suggested as regards the dielectric relaxation process.

Selected hexasubstituted benzenes containing one or two nitro groups and chlorine atoms or methyl groups have been studied in the solid state by means of dielectric, differential scanning calorimetry (DSC), X-ray and Raman techniques. Unknown phase transitions at 223 and 412 K were found in pentachloronitrobenzene (PCNB), and the existence of a rotational phase above 223 K was confirmed with the help of dielectric measurements. In the case of 1,3-dinitrotetramethylbenzene (1,3-DNTMB) and 1,3-dinitrotetrachlorobenzene (1,3-DNTCB) permittivity dispersion in a low-frequency range has not been detected which was interpreted as a lack of rotatory phases in these compounds. No rotational phase in compounds with the angle between the aromatic ring and nitro group planes equal or close to 90° has been found. The crystal structure of 1,3-DNTCB was determined. 1,3-DNTCB crystallizes in P 2 1 / c space group with Z = 4 molecules in a unit cell. DSC data for the studied crystals are quoted for the temperatures from 305 K to the melting point. Low-frequency Raman spectra of the studied compounds are presented and discussed.

The existence of order-disorder type phase transitions around 353 K in 1,2-dinitrotetrachlorobenzene (1,2-DNTCB), found earlier during DSC and dielectric studies, was confirmed on the basis of temperature dependence of selected Raman spectral parameters. It was established that the positions and widths of the studied bands do not vary noticeably near the transition temperature, but the change in their intensity is pronounced and a variation in their shape takes place. As was expected, Raman bands gain gaussian character in the vicinity of the phase transition. The observed properties were consistent with the concept of superstructure formation during phase transition in the 1,2-DNTCB crystal proposed already on the basis of X-ray and dielectric measurements. It was assumed that in the high temperature rotational phase a coupling of molecular movements leads to the collective rearrangement.

The non-linear dielectric effect in dilute solutions of some trans -dipyridylethylenes was investigated. A positive non-linear dielectric effect was found for 1-(2-pyridyl)-2-(2-pyridyl)ethylene and 1-(3-pyridyl)-2-(3-pyridyl)-ethylene, and a negative effect for 1-(2-pyridyl)-2-(3-pyridyl)ethylene, 1-(3-pyridyl)-2-(4-pyridyl)ethylene and 4-styrylpyridine. The results indicated simultaneous overall reorientation and internal reorientation of the pyridyl rings about the CC axis. The free energy of internal rotation was calculated based on Piekara's model.

Dielectric relaxation measurements have been performed on the four isomers 2,2′ -, 2,3′ -, 3.3′ - and 2,4′ -difluorodiphenyl (DFDP) in p -xylene in the frequency and temperature ranges of 1.5–10 GHz and 293–323 K respectively. It has been found that symmetrically substituted derivatives (2,2′ - and 3,3′ -difluorodiphenyls) show a Debye-like pattern and that for non-symmetrically substituted derivatives (2,3′ - and 2,4′ -DFDP) the dielectric absorption differs strongly from this type of pattern. According to the model, this behaviour indicates that in the symmetrical compounds the contribution of the intramolecular rotation can be neglected and that in the case of non-symmetrically substituted derivatives there are two dielectric relaxations connected with internal rotation and overall molecular reorientation respectively. The analysis of the dielectric relaxation times together with moments of inertia is used to obtain further information about the molecular dynamics.

The non-linear dielectric effect in dilute solutions of some trans -dipyridylethylenes was investigated. A positive non-linear dielectric effect was found for 1-(2-pyridyl)-2-(2-pyridyl)ethylene and 1-(3-pyridyl)-2-(3-pyridyl)-ethylene, and a negative effect for 1-(2-pyridyl)-2-(3-pyridyl)ethylene, 1-(3-pyridyl)-2-(4-pyridyl)ethylene and 4-styrylpyridine. The results indicated simultaneous overall reorientation and internal reorientation of the pyridyl rings about the CC axis. The free energy of internal rotation was calculated based on Piekara's model.

Dielectric relaxation and the non-linear dielectric effect have been measured in dilute solutions of monobenzoylferrocene and 1,1′-acetylbenzoylferrocene, and only the non-linear dielectric effect in monoacetylferrocene. The dielectric relaxation was measured in the temperature and frequency ranges of 283–303 K and 1–38 GHz, respectively, and the non-linear dielectric effect in the temperature range of 283–308 K. From the results obtained, it is inferred that in the monosubstituted derivatives, the simple absorption band may be due to reorientation of the whole molecule, and that in the disubstituted ones, there are present two almost-fixed structures between which a slow interconversion is possible.

Dielectric relaxation measurements have been performed on the four isomers 2,2′ -, 2,3′ -, 3.3′ - and 2,4′ -difluorodiphenyl (DFDP) in p -xylene in the frequency and temperature ranges of 1.5–10 GHz and 293–323 K respectively. It has been found that symmetrically substituted derivatives (2,2′ - and 3,3′ -difluorodiphenyls) show a Debye-like pattern and that for non-symmetrically substituted derivatives (2,3′ - and 2,4′ -DFDP) the dielectric absorption differs strongly from this type of pattern. According to the model, this behaviour indicates that in the symmetrical compounds the contribution of the intramolecular rotation can be neglected and that in the case of non-symmetrically substituted derivatives there are two dielectric relaxations connected with internal rotation and overall molecular reorientation respectively. The analysis of the dielectric relaxation times together with moments of inertia is used to obtain further information about the molecular dynamics.

Dielectric relaxation measurements were carried out on three isomers 2,3'-dicyanodiphenyl, 3,3'-dicyanodiphenyl and 4-cyanodiphenyl in p-xylene in the temperature range 293-323 K for static frequencies up to 10 GHz. The analysis of the dielectric dispersion of these compounds was carried out and the mechanism of the internal rotation for these molecules has been proposed.

Dielectric relaxation and non-linear dielectric effect measurements were carried out in 2- and 4-nitrodiazoacetophenone in p -xylene. Linear dielectric measurements have been performed in the frequency and temperature range of 0.50–36 GHz and 293–313 K, respectively. Dielectric absorption for 2-nitrodiazoacetophenone shows Debye-like behaviour, while for 4-nitrodiazoacetophenone one observes a complex curve which indicates some distribution of dielectric relaxation times. From these results information about the molecular dynamics of the dielectric relaxation is obtained.

Dielectric relaxation measurements have been performed on monocrystals of orthodinitrotetramethylbenzene and orthodinitrotetrachlorobenzene in the frequency and temperature ranges 1 kHz-1000 MHz and 280–450 K, respectively. In addition, scanning calorimetric as well as X-ray measurements have been carried out. From the results obtained a possible mechanism has been suggested as regards the dielectric relaxation process.

The dielectric relaxation mechanism of 2,2'- and 3,3'-dibromodiphenyl has been examined from measurements at different frequencies and temperatures. All dielectric measurement have been done on diluted solutions in p-xylene. A simple dielectric absorption band was observed in both cases. It was found that the Goulon-Rivail model provides a good description of the dielectric relaxation mechanism.

Dielectric relaxation measurements were carried out on mono-, and 1,1′-di-benzoylferrocene in p-xylene in the temperature and frequency range of 293–313 K and 7.5–38.2 GHz, respectively, at various concentrations. For both molecules only one absorption was found in the GHz-region, which can be assigned to whole molecule reorientation and/or (less probably) to the internal rotation around the axis perpendicular to the cyclopentadienyl rings. In both cases a Debye-like behaviour was observed. The following macroscopic dielectric relaxation times (τ) were calculated: compound, T/K, τ/ps; monobenzoylferrocene, 293, 39.8; 303, 37.3; 313, 35.0; dibenzoylferrocene, 293, 63.2; 303, 51.9; 313, 41.2. From the Eyring diagram values of 1.6 and 2.3 kcal.mol −1 were obtained, respectively, for the activation enthalpy of mono-, and di-substituted derivative. A comparison was made among the various ferrocenes studied to date in our laboratory.

Several K 4 Me 11 (CN) 6 ·3 H 2 O type cyano complexes belonging to the C 2h crystal class were studied to examine their ferroelectricity and the dielectric-relaxation process. Isomorphous substances obtained through replacing the Fe 2− ion by Ru 2+ , Os 2+ and Mn 2+ ions show ferroelectric behaviour and dielectric relaxation, in both the ferro- and para-electric phases. It was found, through a careful analysis of the shape of the dielectric-absorption band, that a polydispersive nature appears in the whole temperature range explored and becomes very pronounced in the immediate vicinity of the transition temperature. The distribution of the relaxation times has been described by means of the Williams-Watts decay function.

Vibrational correlation functions and corresponding correlation times were determined by a variety of techniques for the v s (GeCl) and sym- v s (Ge(CH 3 ) 3 ) vibrations of trimethylchlorogermane from Raman bandshape analysis. The results clearly show that it is not possible to obtain reliable correlation functions and other related data for these vibrations due to the joint effects of isotopic splitting and Fermi resonances.

Dielectric relaxation measurements were carried out on three trans isomers 1-(2-pyridyl)-2-(4-pyridyl)-ethylene (2.4′-DPE), 1-(2-pyridyl)-2-(3-pyridyl)-ethylene (2.3′-DPE) and 1.2-di-(3-pyridyl)-ethylene (3.3′-DPE) in mesitylene in the temperature range 293–323 K, and from static frequency up to 10.56 GHz. Two dielectric absorption regions were found for 2.4′- and 2.3′-DPE but only one for the third isomer 3.3′-DPE. Dielectric relaxation times as well as thermodynamic activation parameters for the dielectric process were determined and are discussed comparatively. It is deduced that internal rotation very probably takes place around the bonds between the pyridine rings and the ethylene moiety. As regards the model, results were interpreted according to the Goulon-Rivail theory.

The electric dipole moments of some styrene and trans- and cis-stilbene oxides have been measured, in benzene. From these data some bond angles have been calculated and it has been deduced that in the styrene derivatives the phenyl group is in rapid interconversion about the bond with the triatomic ring.

The electric dipole moments of acetyldiazomethane (MeCOCHN2) and 1-acetyl-1-diazo-ethane (MeCOMeN2) between 10 and 70 °C have been measured. Using appropriate group and bond moments, the concentrations of the two rotamers present in each have been calculated and, hence, the equilibrium constant for the cis ⇆ trans equilibrium at the various temperatures. The change in standard enthalpy (⊿H°), standard free energy (⊿G°) and standard entropy (⊿S°) are reported for the conversion of one mole of cis isomer to trans isomer.

The effects of electronic structure and conformation of the molecules (Y = o, m, and p-Cl) and (Y′ = o, and m-Cl) have been studied in benzene between 10.0 and 70.0 °C. In the oxirane systems the conjugation between the two rings is very small, if present at all; consequently, in the absence of steric and/or electrostatic hindrance internal rotation is observed. In the cyclopropane systems examined these steric effects are sufficiently important to completely immobilise the molecular structure.

The dielectric relaxation of deuterated K 4 Me 11 (CN) 6 ·3H 2 O doped with NH 4 1 has been investigated in the vicinity of the transition temperature. In all cases the dielectric band appeared to be non-symmetrical and may be described by means of the Williams-Watts empirical decay function ϕ(Φ) ⇌ exp[−(−/τ - )]. A mechanism for the asymmetry of the dielectric absorption due to fluctuation of the “Glarum defects” is proposed. Also, the nature of the dielectric absorption in the crystals is discussed.

Dielectric relaxation measurements have been carried out on 3-methyl-1,5-diphenyl-1,4-pentadiyn-3-ol in p-xylene, in the frequency and temperature ranges 1.7–10.6 GHz and 293–323 K, respectively, and the i.r. spectra in several solvents and in the solid state have been recorded. From the i.r. measurements it has been inferred that dimers are present only to a very limited extent and that clusters are absent at all the concentrations examined. From the dielectric measurements, monodispersive behaviour of the Debye type has been found in the frequency range explored, this being assigned to relaxation of the hydroxy group.

Dipole moments have been measured in n-decane at 5–130°C for the compounds monochloro-, 1,1′-dichloro-, monobromo-, 1,1′-dibromo-, monoiodo-, and 1,1′-diiodo-ferrocene. The energy barriers (ΔE1 = E36° - E18 o° and ΔE2 = E108° - E180°) to rotation of the two cyclopentadiene rings about the bond to iron have been calculated. Conclusions are reached about the principal energy contributions giving rise to the barrier.

The electric dipole moments of the complexes π-LFe(CO)3, where L = trans-PhCHCHCHO, trans-PhCHCHCOMe, trans-PhCHCHCOPh, trans, trans-PhCHCHCHCHPh and CH2CHCHO, have been measured. The preparation of the last two complexes is also described. A vectorial analysis of the moments leads to the conclusion that the complexes are π in type, i.e. the aldehyde and ketone ligands bond to the iron via the olefinic and carbonylic bond and do not involve the oxygen lone pairs. The metal to ligand back-bonding is stronger in the aldehyde and ketone complexes than in the butadiene ones.

The dielectric relaxation of the three symmetrically substituted diaryl ketones: 2,2′-dipyridyl ketone (2,2′-DPyCO), dimesityl ketone (DMCO) and 3,3′-dinitromesityl ketone (3,3′-DNDMCO) in p -xylene was examined over the frequency range 2–30 GHz, at 293–323 K. A distribution of relaxation times was observed for 2,2′-DPyCO and the average value for τ 0 was found to be lower than for fluorenone. The absorption in the case of DMCO and 3,3′-DNDMCO is monodisperse. A comparison of the relaxation times of these molecules suggests the possibility of a contribution from the intramolecular rotation of the pyridyl rings in 2,2′-DPyCO. The relaxation mechanism of 2,2′-DPyCO is discussed in terms of the Fong and Goulon-Rivail theories.

C10H12N2O4 (Mr=224.2) crystallizes in the triclinic system, space groupP¯1 witha=8.327(3),b=8.734(3),c=8.453(3) A;a=63.6(1),β=97.0(1), γ=100.4(1)°;V=541.0(6) A3,Z=2,Dc=1.38 g cm−3,μ(Cu-Kα)=8.7 cm−1, λ=1.5418 A, F(000)=236. Deviation from theoretic geometry of the benzene ring and from planarity is observed in accordance with theσ-electron-withdrawing character of the NO2 groups and the high steric hindrance of the substituents.

Dielectric spectra, of formyl-, carboxyl-, and 1, 1'-dichloro-ferrocene have been examined in benzene in the frequency range of 100 MHz– 26 GHz, at various temperatures. In these conditions only one clear dielectric absorption band has been observed and a Debye-type behaviour has been found. Calculation of the macroscopic dielectric relaxation times and the thermodynamic parameters has also been performed.

Dielectric absorption measurements have been carried out on two trans-1,2-di-(2-pyridyl)- (2,2′-DPE) and 1-(3-pyridyl)-2-(4-pyridyl)-ethylenes (3,4′-DPE) and on trans-styrylpyridine in mesitylene in the temperature range 293–323 K, and from a static frequency up to 10 GHz. The results are interpreted in terms of relaxation both via overall molecular motion and by internal rotation. The model of “chemical relaxation” (Goulon—Rivail) is shown to be very useful and kinetic parameters are obtained. Semi-empirical calculations have also been performed for 2,3′-DPE.

It is shown that α,α-dicyclohexyl-cyclohexanemethanol (TCHC) in the low temperature phase (below 104 K) forms fixed, open dimers and in the high temperature phase (104–369 K) open dimers, dynamically cyclic. This is a first example of an alcohol compound forming open dimers in the crystalline phase. Temperature dependence of the Raman (113–369 K) and IR (15–369 K) spectra reveal the existence of coupling of some lattice vibrations with the ν(OH⋯O) stretching vibrations of the dimer.

An analysis of the dielectric dispersion for 2- and 3-phenylpyridines has been carried out in order to derive a theoretical model for dielectric relaxation process.

Polarized IR and Raman spectra have been measured for meta‐dinitrotetramethylbenzene single crystals. Using different scattering and polarization geometries in the Raman effect and polarized reflectance and transmission infrared spectra, all the polarizability tensor matrix elements and electric dipole moment variations have been determined for the monoclinic crystal of this molecule. Lifting of degeneration, at the Brillouin zone center, of the longitudinal and transverse components of the infrared phonons have been detected and attributed to long range electrostatic interactions of the molecules in the unit cell.

The electric dipole moments of the complexes π-LFe(CO)4, where L =trans-PhCHCHCOCH3, trans-PhCHCHCOPh, trans-PhCHCHCHO, CH2HCHO, and CH2CHCN, have been determined. It is found that the ligand plane is never parallel to the axis of the trigonal bipyramid. The ligand CO group in the carbonyl derivatives is slightly out of the CCC plane. The structure of the acrylonitrile complex in solution is the same as that found for the solid from X-ray studies. The ketone iigands have the same conformation in the complex as in the free ligand. The aldehyde ligands. present only as the s-trans-conformer in the free state, form both isomers when bonded to the metal. The enthalpy variation for the conformational equilibrium s-cis⇄s-trans for the aldehyde complexes has been ca culated from i.r. data, and an assignment of the CO stretchings has been proposed.

Semiempirical CNDO/2 calculations have been applied to the rotational isomerism of the hindered α-diazo ketones CH2ClCOCHN2 and CH3COCCH3N2. It is concluded that the cis form is the more energetically stable for the chloroderivative, whilst both cis and trans forms are present in the other compound. These results are in agreement with spectroscopic measurements and experimental electric dipole moments.

Semiempirical CNDO/2 calculations have been performed on the series of compounds phenylcyclopropane, phenyloxiran, phenylthiiran, phenylaziridine, and 1,1-dichloro-2-phenylcyclopropane. From the energies obtained, it is concluded that for all these molecules the most stable conformation is that in which the planes of the phenyl group and of the three-membered ring are orthogonal (or very close to orthogonal) to one another. These results indicate that inter-ring conjugation is present. The energy barrier to rotation about the phenyl–threemembered ring bond is ⩽ 13.4 kJ mol–1 for the first four compounds, which suggests that interconversion between one orthogonal form and another, equivalent to the first, is rapid at room temperature. Instead, 1,1-dichloro-2-phenylcyclopropane, because of the steric and electrostatic effects of the chlorine atoms, gives an energy barrier of 61.9 kJ mol–1. For this reason interconversion in this molecule is slow.

The mass spectra of substituted ferrocenes have been reinvestigated making intensive use of the metastable ions. The observed primary fragmentation of the molecular ions are different in some respects from those previously postulated. The study of the metastable ions characteristics of the ions at m/z 186 and m/z 121 indicates that their structures are independent of their precursor ions.

Dielectric spectra of formyl-, carboxyl-, and 1,1′-dichloro-ferrocene have been examined in benzene in the frequency range of 100 MHz-26 GHz, at various temperatures. In these conditions only one clear dielectric absorption band has been observed and a Debye-type behaviour has been found. Calculation of the macroscopic dielectric relaxation times and the thermodynamic parameters has also been performed. All evidence seems to suggest a type of mechanism for dielectric relaxation, even if at the present stage of research it might be prudent not to indicate a definitive model for the molecular dynamics itself of these compounds.

A complete molecular dynamic study of monoacetylferrocene has been carried out in p-xylene using dielectric relaxation measurements in the frequency range of 700 MHz-38 GHz at temperatures of 293, 303, 313, and 323 K and at concentrations that vary from 0 to 3% by weight. Under these conditions no intermolecular association or interaction of any type was observed between the solute molecules. As was expected, the compound absorbed in the GHz-region, there being just one very sharp band. At the present stage of our inquiry, this may be assigned to rotation around the molecular axis perpendicular to the two cyclopentadienyl rings or to the molecular reorientation. Treatment of the real and imaginary parts of the complex dielectric permittivity obtained at a concentrarion of 3% (weight fraction) clearly confirmed that the behaviour is very similar to that predicted by the Debye theory. The following macroscopic dielectric relaxation times were calculated: T/K, τ/ps; 293, 26.15; 303, 22.88; 313, 20.66; 323, 18.31. Analysis of these data by means of an Eyring diagram gave the following values for the parameters of the activation of the dielectric relaxation process: ΔH*=1.63±0.3 kcal.mol−1 and ΔS*=−4.86 e.u.