NQR study of the structure and structural transitions of chloroprene rubbers

The microstructures of some chloroprene rubbers, chloroprene-styrene copolymer and chloroprene-dichlorobutadiene copolymer, have been examined by nuclear quadrupole resonance (NQR). Molecular motions in the chloroprene rubber “nairit NP” have also been studied by NQR. It is shown that above 150 K the temperature-dependence of NQR frequencies differs for oriented and non-oriented samples. Molecular motions during unfreezing processes in the temperature range of polymer brittleness are manifested in NQR spectra by decrease of the frequency temperature coefficient.     

Temperature dependence of 35Cl NQR in 2,6-dichloropyridine

Chlorine NQR in 2,6-dichloropyridine has been investigated in the temperature range 77 K to room temperature and a single resonance line has been observed throughout. Using this data, torsional frequencies of the molecule have been evaluated on the basis of both the Bayer theory and the modified Bayer theory incorporating Tatsuzaki correction.     

35Cl NQR frequency and spin lattice relaxation time in 3,4‐dichlorophenol as a function of pressure and temperature

The pressure dependences of ³⁵Cl nuclear quadrupole resonance (NQR) frequency, temperature and pressure variation of spin lattice relaxation time (T₁) were investigated in 3,4‐dichlorophenol. T₁ was measured in the temperature range 77–300 K. Furthermore, the NQR frequency and T₁ for these compounds were measured as a function of pressure up to 5 kbar at 300 K. The temperature dependence of the average torsional lifetimes of the molecules and the transition probabilities W₁ and W₂ for the Δm = ±1 and Δm = ±2 transitions were also obtained. A nonlinear variation of NQR frequency with pressure has been observed and the pressure coefficients were observed to be positive. A thermodynamic analysis of the data was carried out to determine the constant volume temperature coefficients of the NQR frequency. An attempt is made to compare the torsional frequencies evaluated from NQR data with those obtained by IR spectra. On selecting the appropriate mode from IR spectra, a good agreement with torsional frequency obtained from NQR data is observed. The previously mentioned approach is a good illustration of the supplementary nature of the data from IR studies, in relation to NQR studies of compounds in solid state. Copyright © 2012 John Wiley & Sons, Ltd.     

Bromine NQR study of structure and molecular torsional motion in N4P4Br8 and N3P3Br6

The bromine NQR spectrum of tetrameric bromocyclophosphazene, N₄P₄Br₈, has been studied in the temperature range from 77 to 300 K. The negative temperature coefficients of the resonance frequencies have been analysed using Bayer-Kushida-Brown equations. Torsional modes in the frequency range 10–15 cm^?1 are shown to characterise the observed motional averaging and are only slightly temperature dependent. The multiplicity and relative intensities of resonances in the trimer, N₃P₃Br₆, have been correlated with the known electron density distribution. The results for the bromo-derivatives are compared with those reported for the corresponding chloro-derivatives.     

14N NQR study of polymorphism and hydrogen bonding in molecular complex isonicotinamide-oxalic acid (2:1)

The complete (14)N nuclear quadrupole resonance (NQR) spectra have been measured in the two polymorphic crystalline phases of the molecular complex isonicotinamide-oxalic acid (2:1) by nuclear quadrupole double resonance. The observed NQR frequencies, quadrupole coupling constants, and asymmetry parameters (η) have been assigned to the two nitrogen positions (ring and amide) in a molecule on the basis of the intensity and multiplicity of the double resonance signals. The NQR data for the ring nitrogen in both polymorphic phases deviate from the correlation relations observed in substituted pyridines. This deviation is analyzed in a model, where it is assumed that an additional electric charge on the nitrogen atom changes the NQR parameters. The model suggests that this additional electric charge is negative so that the N···H-O hydrogen bond seem to be partially ionic, of the type N(-)···H-O.     

NQR Studies of the chloro(amino)cyclotriphosphazenes,N3P3(NHCH2·CH2NH)Cl4, N3P3(NHBut)4Cl4 and N3P3(NHBut)4Cl2

The frequencies and variable-temperature behaviour of ³⁵Cl nuclear quadrupole resonance in three aminocyclophosphazene derivatives are reported. The observed frequencies and multiplicity are correlated with the disposition of the substituents and the crystal structure. The temperature-dependence data are discussed in the framework of Bayer-Kushida-Brown equations and low-lying torsional (librational) frequencies and their average temperature coefficients are estimated. Brown's parabolic equation provides a good fit to the experimental data. Variable-temperature proton FT-NMR measurements (at 270 MHz) have also been carried out. The results are consistent with the NQR data and indicate the presence of two-site chemical exchange of the -NH protons and hydrogen bonding.     

The temperature dependence of 14N NQR frequencies and relaxation times for 4-methoxyaniline.

The ¹⁴N resonance frequencies and relaxation times, T₂^★, have been measured between 77 K and 298 K with a low power transient method (S.R.O.). Comparative NQR data from a high power transient method (Pulse-F.T.) has been measured at 77K and 298 K. There is evidence that the high power transient method narrows lines at room temperatures. The temperature study found a sudden change in the NQR frequencies and T₂^★′s between 210 K and 250 K. Differential Scanning Calorimetry narrowed the range to 224±2 K. The observations suggest a crystallographic phase change. A simple model considers the thermal motion of the NH₂ substituent within a symmetrical potential well with 3 minima, and accounts for the sudden change in the EFG symmetry and the detection of 2 sets of NQR frequencies soon after the sample has been quenched in a 77 K temperature bath. With the high power transient system a ～ 6kHz splitting in the 77 K NQR frequencies has been measured. The observation is consistent with the crystallographic structure of molecular analogs.     

Pressure and temperature dependence of the chlorine NQR in caesium and sodium chlorates

The (35)Cl nuclear quadrupole resonance (NQR) frequencies (nu(Q)) in caesium and sodium chlorates were measured as a function of temperature, from 77 to 300 K at different pressures up to 5.1 kbar, and the data were analysed to estimate the volume dependence of the electric field gradient (EFG), torsional frequency and also the contributions to the NQR frequency from static and dynamic effects. The variation of spin-lattice relaxation time with pressure at different temperatures was studied in the case of sodium chlorate and at room temperature in case of caesium chlorate. The pressure dependence of the spin-lattice relaxation time (T(1)) suggests that the relaxation is mainly due to the torsional motions.     

14N NQR study of nicotinamide and related compounds

14N nuclear quadrupole resonance (NQR) frequencies have been measured in picolinamide, nicotinamide, isonicotinamide, 2,6-pyridine dicarboxamide, and acetamide by double resonance. The 14N NQR spectra in picolinamide, nicotinamide, isonicotinamide, and 2,6-pyridine dicarboxamide show the presence of two distinct nitrogen positions: the ring position with the quadrupole coupling constant about 4,5 MHz and the amide position with the quadrupole coupling constant about 2.6 MHz. The NQR data are related to the structure of the investigated compounds and to the N--H...O hydrogen bonds.     

Synthesis of diethynyltriptycene-linked dipyridyl ligands

[reaction: see text] An efficient route to a new family of dinucleating ligands has been developed. A convergent strategy to these ligands involved dual Sonogashira cross-coupling of 2,3-diethynyltriptycene with a variety of functionally diverse 5-bromopyridines. The resultant ligands were accessed in four steps and 40-50% overall yield from 1,2,4,5-tetrabromobenzene. Synthesis of an imidazole and a quinoline derivative by this method is also described.     

1H-17O nuclear quadrupole double resonance in phenylphosphinic acid and phenylphosphonic acid. 17O quadrupole coupling in P = O and P-O-H bonds

The (17)O nuclear quadrupole resonance (NQR) frequencies have been measured in phenylphosphinic acid and phenylphosphonic acid using nuclear quadrupole double resonance. The quadrupole coupling constants have been determined with an uncertainty of +/- 10 kHz and the asymmetry parameter eta with an uncertainty of +/- 0.01. The results are compared to the published results of the theoretical calculation and the high-field solid-state NMR measurements. The position of hydrogen in the O-H...O hydrogen bond in phenylphosphinic acid has also been determined. On the basis of the present and the previously published data we show that the principal values of the electric-field-gradient tensor in P = O and P-O-H bonds correlate. A correlation between the nuclear quadrupole parameters and the length of the P-O bond is also observed.     

Properties of AT cut gallium phosphate resonators

Gallium phosphate is a quartz analogue that possesses more intense piezoelectric properties. We report here a study performed to determine more accurately the properties of resonators made using crystal orientations situated near the main cut presenting a zero temperature coefficient at room temperature. Recent crystals having a much improved quality were used to cut plano-convexe resonators with five orientations situated in a range of nearly two degrees around the previously determined angular position of this cut. The temperature coefficients of the resonance frequencies of the electrically excited shear modes and the electrical properties of the resonators were determined. The vibration modes were studied using synchrotron radiation X-ray topography. For all the studied cuts, parabolic thermal variations of the resonance frequencies were observed. The temperature of the extremum varies somewhat with the rank of the mode and also, but slowly, with the cut angle. On the whole a very good thermal stability is obtained for the resonators. Q factors higher than those previously measured were obtained together with, as predicted, very interesting values of the equivalent electrical scheme. The observed vibration modes are generally close to those computed using the Tiersten theory. They present several very interesting properties but display several particularities, such as often possessing a second shear component with a noticeable amplitude, which make them somewhat different from the mode of the corresponding quartz resonators.     

Dependence of (35)Cl NQR on hydrogen bonding and temperature in dichlorophenol-aniline charge transfer complexes

The hydrogen-bonded charge transfer complexes of aniline with pi-acceptors (or proton donors) such as 2,5-, 2,6-, 3,4- and 3,5-dichlorophenol were prepared. The (35)Cl nuclear quadrupole resonance (NQR) frequencies of these charge transfer complexes in the temperature range 77-300 K were measured to ascertain the existence or otherwise of a phase transition upon complex formation. Further, the NQR frequency and asymmetry parameter of the electric field gradient at the site of quadrupole nucleus were used to estimate the chemical bond parameters, namely ionic bond, double bond character of the carbon-chlorine(C--Cl) bond and the percentage charge transfer between the donor-acceptor components in charge transfer complexes. The effect of hydrogen bonding and temperature on the charge transfer process is analysed.     

Correlation between proton transfer and 35Cl NQR frequency as well as molecular geometry of chloranilic acid in co‐crystals with some organic bases

Proton transfer in hydrogen‐bonded organic co‐crystals of chloranilic acid with some organic bases was investigated by nuclear quadrupole resonance (NQR) spectroscopy. The ³⁵Cl NQR frequencies of chloranilic acid molecule as well as ¹⁴N NQR frequencies of the organic base molecule were measured with the conventional pulse methods as well as double‐resonance methods, respectively. The extent of proton transfer in the O···H···N hydrogen bond was estimated from Townes–Dailey analysis of the ¹⁴N NQR parameters. The ³⁵Cl NQR frequency and molecular geometry of chloranilic acid are correlated to the extent of proton transfer in the protonation process of the organic base molecule. It is shown that the hydrogen bond affects the π‐electron system of chloranilic acid. Geometry dependence of the O···H···N hydrogen bond, i.e. the H? N valence bond order versus the hydrogen‐bond geometry correlation is also discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

Pd catalyzed coupling of 1,2-dibromoarenes and anilines: formation of N,N-diaryl-o-phenylenediamines

1,2-Dibromoarenes were coupled with aniline derivatives to yield N,N-diaryl-o-phenylenediamines in moderate to good yield using a palladium/phosphine or palladium/carbene catalyst system. Under similar conditions, 1,2,4,5-tetrabromobenzene was coupled with aniline derivatives to produce the corresponding tetrasubstituted derivatives which are oxidized on workup to yield azophenines. The sequential reaction of two different anilines with 1-chloro-2-iodobenzene afforded mixed N,N-diaryl-o-phenylenediamines.     

Relation between 35Cl NQR frequencies and spin-lattice relaxation times in HGeCl3

An equation relating ³⁵Cl NQR frequencies toinverse spin-lattice relaxation times was found for HGeCl₃ crystalline phases. The equation was used to identify shortand long-range order contributions to the NQR frequency in the environment of the resonance chlorine atom. Changes in the strength of local electric fields caused by the crystal field were determined.     

Conformations and intermolecular interactions pattern in solid chloroxylenol and triclosan (API of anti‐infective agents and drugs). A 35Cl NQR, 1H‐14 N NQDR,X‐ray and DFT/QTAIM study

Two antibacterial and antifungal agents, chloroxylenol (4‐chloro‐3,5‐dimethyl‐phenol) and triclosan (5‐chloro‐2‐(2’,4’‐dichlorophenoxy)‐phenol), were studied experimentally in solid state with an X‐ray, ³⁵Cl‐nuclear quadrupole resonance (NQR) and ¹⁷O‐nuclear quadrupole double resonance (NQDR) spectroscopies and, theoretically, with the density functional theory/quantum theory of atoms in molecules (DFT/QTAIM). The crystallographic structure of triclosan, which crystallises in space group P3₁ with one molecule in the asymmetric unit [a = 12.64100(10), b = 12.64100(10), c = 6.71630(10) Å], was solved with an X‐ray and refined to a final R‐factor of 2.81% at room temperature. The NQR frequencies of ³⁵Cl and ¹⁷O were detected with the help of the density functional theory (DFT) assigned to particular chlorine and oxygen sites in the molecules of both compounds. The NQR frequencies at ³⁵Cl sites in chloroxylenol and triclosan were found to be more differentiated than frequencies at the ¹⁷O site. The former better describes the substituent withdrawing effects connected to π‐electron delocalization within the benzene rings and the influence of temperature; whereas, those at the ¹⁷O site provide more information on O‐H bond and intermolecular interactions pattern. The conformation adopted by diphenyl ether of triclosan in solid state was found to be typical of diphenyl ethers, but the opposite to those adopted when it was bound to different inhibitors. According to an X‐ray study, temperature had no effect on the conformation of the diphenyl ring of triclosan, which was the same at 90 K and at room temperature (RT). The scattering of NQR frequencies reproduced by the DFT under assumption of the X‐ray data at 90 K and RT is found to be a good indicator of the quality of resolution of the crystallographic structure. Copyright © 2012 John Wiley & Sons, Ltd.     

An ab initio quantum chemical investigation of solvent-induced effect on 14N-NQR parameters of alanine,glycine, valine,and serine using a polarizable continuum model

In this paper ab initio quantum mechanical calculations of the ¹⁴N-nuclear quadrupole resonance (NQR) parameters of alanine, glycine, valine, and serine obtained from an electric field gradient (EFG) tensor, such as quadrupole frequencies and asymmetry parameters in gas phase and different solvents, have been carried out with the Gaussian 98 software package and the solvent-induced effects on these parameters have been evaluated using density functional theory (DFT). Furthermore, direct and indirect solvent effects on asymmetry parameters have been also calculated. We determined that the NQR parameters of the nitrogen atoms of amino acids are highly sensitive to environmental effects and that the observed solvent-induced shielding variation is strongly related to the values of the dielectric constants of the solvent and whether it is protic or aprotic. For more investigation of the solvent effect, the relative energies of each amino acid in various solvents have been calculated and the graphs of the relative energies versus dielectric constants have been analyzed.     

Temperature dependence of one-dimensional hydrogen bonding in morpholinium hydrogen chloranilate studied by (35)Cl nuclear quadrupole resonance and multi-temperature X-ray diffraction

The temperature dependence of (35)Cl NQR frequencies and the spin-lattice relaxation times T(1) has been measured in the wide temperature range of 4.2-420 K for morpholinium hydrogen chloranilate in which a one-dimensional O-HO hydrogen-bonded molecular chain of hydrogen chloranilate ions is formed. An anomalous temperature dependence of the NQR frequencies was analyzed to deduce a drastic temperature variation of the electronic state of the hydrogen-bonded molecular chain. The hydrogen atom distribution in the OHO hydrogen bond is discussed from the results of NQR as well as multi-temperature X-ray diffraction. Above ca. 330 K, the T(1) showed a steep decrease with an activation energy of ca. 70 kJ mol(-1) and with an isotope ratio (37)Cl T(1)/(35)Cl T(1) = 0.97 ± 0.2. The orientational change of the z axis of electric field gradient tensor in conjunction with the hydrogen transfer between adjacent hydrogen chloranilate ions is suggested as a possible relaxation mechanism.     

Cl35 nuclear quadrupole resonance spectra of chloro-substituted 6-pyridazone derivatives

The effect of substituents in the pyridazone ring (including the carbonyl oxygen atom) on the chlorine atoms in the 3,4, or 5 positions was investigated on the basis of data from the Cl³⁵ nuclear quadrupole resonance (NQR) spectra of chloro-substituted 6-pyridazones. The NQR frequencies of 1-phenyl-4,5-dichloro-6-pyridazone were compared with the reactivities of chlorine atoms in this compound in nucleophilic substitution reactions.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No.3, pp. 392–395, March, 1976.