Comparative analysis of the applicability of AM1 and CNDO/2 methods for quantitative prediction of the35Cl NQR frequencies of RC-Cl compounds

The³⁵Cl NQR frequencies of a series of RC-Cl compounds were calculated by the AM1 and CNDO/2 methods in the Townes-Dailey approximation. It was shown that neither of these methods can be directly used for the quantitative prediction of NQR frequencies, and their use in the correlation approach is only possible in narrow series. The AM1 method gives better results for saturated compounds.Institute of Organic and Physical Chemistry, Kazan' Scientific Center, Russian Academy of Sciences, 420083 Kazan'. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 5, pp. 1078–1082, May, 1992.     

Theoretical study concerning the reactivity of imine derivatives of polycyclic aromatic hydrocarbons

The opening reaction of N-protonated polycyclic aromatic hydrocarbon imines has been computed by means of ab initio, density functional, and semiempirical methods of calculation. Imines are predicted to be more stable than the corresponding O-protonated derivatives, epoxides and diol epoxides. On the other hand, the activated N-methanesulfonylbenzene imine presented more favorable DeltaE( not equal ) and DeltaE(r) for ring opening due to the effect of hydrogen-bond interactions. Anti and syn trans-diol benzene imines did not show a different behavior from the unsubstituted imine. According to these calculations, bay-region, fjord-region, and bay-region methyl-substituted compounds opened more easily among the imine derivatives, following the same reactivity pattern as the oxygen analogs. The exothermicity of the opening process correlated with the charge delocalization in the resulting carbocation.     

The purity of SnCl4 as monitored by 35Cl nuclear quadrupole resonance

The nuclear quadrupole resonance (NQR) spectroscopy was used to control the comparative purity of three SnCl₄ samples subjected to successive stages of deep purification. The results showed that at 77 K the samples were identical in purity degree due to the ‘freezing’ of impurities into a separate fraction not affecting the perfection of the SnCl₄ crystal lattice. The results of relaxation measurements suggest that paramagnetic impurity atoms (Fe and Cr) contained in the samples in small amounts might be embedded into the crystal lattice causing extremely long spin–spin relaxation time.     

cis–trans Isomerisation of Substituted Aromatic Imines: A Comparative Experimental and Theoretical Study

The cis–trans isomerisation of N‐benzylideneaniline (NBA) and derivatives containing a central C?N bond has been investigated experimentally and theoretically. Eight different NBA molecules in three different solvents were irradiated to enforce a photochemical trans${{\mathop \rightarrow \limits ^{h\nu }_{}}}$ cis isomerisation and the kinetics of the thermal backreaction cis${{\mathop \rightarrow \limits ^{\Delta }_{}}}$ trans were determined by NMR spectroscopy measurements in the temperature range between 193 and 288 K. Theoretical calculations using density functional theory and Eyring transition‐state theory were carried out for 12 different NBA species in the gas phase and three different solvents to compute thermal isomerisation rates of the thermal back reaction. While the computed absolute rates are too large, they reveal and explain experimental trends. Time‐dependent density functional theory provides optical spectra for vertical transitions and excitation energy differences between trans and cis forms. Together with isomerisation rates, the latter can be used to identify “optimal switches” with good photochromicity and reasonable thermal stability.     

Synthesis of Prochiral Imines from Aromatic Ketones Using Magnesium Perchlorate as Catalytic Promotor

We report the synthesis of new prochiral imines by the reaction of nonsymmetric benzophenone derivates, bencylamines, and anilines in good yields. All the products were characterized by ¹H and ¹³C NMR as an isomeric E/Z mixture. Also, the molecular structures for five derivatives determined by single-crystal x-ray experiments are presented.

Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.     

Analysis of the effect of the electronic structure of the Cl atom in complexes of chlorides of group IV elements on Cl NQR frequency and asymmetry parameter

Analysis of changes in ³⁵Cl NQR frequency of complexes MCl₄.L and MCl₄.2L for M = Si, Ge, Sn and Ti was performed. The population of the atomic orbitals was calculated by the quantum chemistry methods PM3 and INDO. The results provided an explanation of the changes in ³⁵Cl NQR frequency and the asymmetry parameter upon complex formation. In the complexes of non-transition elements, a decrease in ³⁵Cl NQR frequency is first of all related to increasing population of p_z orbitals on Cl atoms. In the complexes of Ti, the increase in ³⁵Cl NQR frequency depends on a decrease in the p_π to d_π electron density transfer.     

Analysis of the effect of the electronic structure of the Cl atom in complexes of chlorides of group IV elements on Cl NQR frequency and asymmetry parameter

Analysis of changes in ³⁵Cl NQR frequency of complexes MCl₄.L and MCl₄.2L for M = Si, Ge, Sn and Ti was performed. The population of the atomic orbitals was calculated by the quantum chemistry methods PM3 and INDO. The results provided an explanation of the changes in ³⁵Cl NQR frequency and the asymmetry parameter upon complex formation. In the complexes of non-transition elements, a decrease in ³⁵C1 NQR frequency is first of all related to increasing population of p_z orbitals on Cl atoms. In the complexes of Ti, the increase in ³⁵Cl NQR frequency depends on a decrease in the p_π to d_π electron density transfer.     

NQR study of chalcogenide glasses Ge-As-Se

A three‐component Ge‐As‐Se system is studied by the nuclear quadrupole resonance (NQR) method on ⁷⁵As nuclei and by the nutation NQR spectroscopy. The NQR ⁷⁵As spectra of the glasses Ge_0.021As_0.375Se_0.604, Ge_0.043As_0.348Se_0.609 and Ge_0.068As_0.318Se_0.614reveal broad lines with two peaks assigned to the main structural unit of As₂Se₃. With increasing average coordination number (r?), the spectrum signals are shifted towards higher frequencies. At r? > 2.54, the spectrum becomes complex, which is a consequence of formation of more complex molecular structures in the glasses of high content of germanium. At fixed frequencies the asymmetry parameter η of the samples studied is determined. Copyright © 2011 John Wiley & Sons, Ltd.     

用核磁共振方法表征芳香酯环状二聚体

用＾１Ｈ，＾１３ＣＮＭＲ方法研究了芳香酯环状二聚体的结构，并讨论了芳香酯环状二聚体的＾１Ｈ谱和＾１３Ｃ谱各谱峰的归属，为同类化合物的表征提供了一个依据。     

Structure determinations of nitrogen compounds with the aid of NQR, NMR, and ESCA spectroscopy

Since it is often necessary or desirable to determine the structures of compounds containing nitrogen directly via the nitrogen atoms, the nuclear quadrupole resonance (NQR) and the nuclear magnetic resonance (NMR) as well as the photoelectron and the Auger-electron spectroscopy (ESCA) of nitrogen are becoming increasingly important. A comparative review of these three methods on the basis of measurement effect, information obtainable, applications, and limitations forms the subject of this article.     

Ab initio and MNDO Calculations of Cyanuric Chloride,its 35Cl NQR Frequency and Asymmetry Parameter of the EFG at the 35Cl Nuclei

Ab initio molecular orbital calculations of the (CNCl)₃ (cyanuric chloride; 2,4,6-trichloro-1,3,5-triazine) molecule were performed at the RHF/6–31G* level. The ³⁵Cl NQR frequency and asymmetry parameter of the EFG at the ³⁵Cl nucleus were calculated from the total populations of the Cl atom valence p-orbitals and their components. The ³⁵Cl NQR frequency and asymmetry parameter which are determined for (CNCl)₃ based on these components agree well with the corresponding experimental values and demonstrate the importance of including the less diffuse components of the p-orbitals.     

Conformational features of Cl3P=NC(CF3)3 and Cl3P=NCCl(CCl3)2 molecules according to results of non-empirical calculations

Non-empirical RHF/6-31G* and MP2/6-31G* quantum chemical methods are used to calculate the molecular structure of trichlorophosphazene compounds: Cl₃P=NC(CF₃)₃ (I) and Cl₃P=NCCl(CCl₃)₂ (II). The corresponding geometric parameters obtained from the calculations are compared with X-ray diffraction analysis data reported in the literature. Conformational differences between the molecules of I and II, previously found by X-ray diffraction in the crystals of these compounds, are confirmed by non-empirical calculations of the molecules in the free state. The features of their geometry caused by intramolecular interactions are discussed.     

N NQR in the tetrazole family

¹⁴N NQR frequencies and spin–lattice relaxation times were measured in technologically important 5-aminotetrazole and 5-aminotetrazole monohydrate at different temperatures between 77 K and 300 K. Five NQR triplets ν₊, ν₋ and ν₀ were found for the five inequivalent nitrogen atoms in each compound between 0.7 MHz and 4 MHz. Carr-Purcell based multipulse sequences were used to accumulate quadrupole echo signals before the FFT analysis. Assignment of the frequencies to atomic positions was made and the results are analysed in relation to the molecular chemical bonds and possible H-bonds in the crystal structures. The new NQR frequencies are reasonably related to the previously published NQR spectrum of the third family member, 1H-tetrazole.     

Assessment of substituent effects on the parameters of 35Cl nuclear quadrupole resonance in para‐substituted benzene‐sulphenyl chloride via quantum chemical calculations

In this research, substituent effects on the parameters of ³⁵Cl nuclear quadrupole resonance (NQR) in para‐substituted benzene‐sulphenyl chloride were studied at M062X/6‐311G(d,p) theory level. The ³⁵Cl NQR parameters of the quadrupole coupling constant (QCC) and electric‐field gradient (EFG) tensor, as well as an asymmetric parameter, were shown to be correlated with Hammett constant following their calculations. The frontier orbital energy levels, HOMO‐LUMO gaps, hardness, electrophilicity, and chemical potential values of these molecules were calculated as well. natural bond orbital (NBO) analysis was applied for calculating natural populations at chlorine atoms.     

Effect of acid on the quantum yield of photodissociation of 9-(4-azidophenyl)acridine

The quantum yield of photodissociation of 9-(4-azidophenyl)acridine (1) is equal to 0.82, and that of its protonated form 2 is 6.9·10⁻³. The observed quantum yield of the system can smoothly be controlled in these limits varying the acidity of the medium. According to quantum chemical data, reactivity difference between neutral azide 1 and cation 2 is caused by the fact that in the lowest singlet-excited state (S₁) of azide 1 the antibonding σ*_NN molecular orbital is occupied, while this orbital remains unoccupied in the excited state of cation 2. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2655–2660, December, 2005.     

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.     

Stereoelectronic structure of MCl4-benzoyl chloride (M=Si,Ge, Sn) systems resulting from ab initio calculations and NQR 35Cl

Results of quantum-chemical calculations of MCl₄–C₆H₅COCl (M=Si, Ge, Sn) systems of 1?:?1 composition using RHF/3-21?G* and MP2/3-21?G* levels as well as those of 1?:?2 composition using the RHF/3-21?G* level have been represented. MCl₄?←?C₆H₅COCl complexes of 1?:?1 composition are energetically more advantageous. They are formed in solid state provided that the M···O distance in individual systems is considerably less than the sum of van der Waals radii of M and O and their total energies are appreciably less than the sum of total energies of components. These conditions are realized only for M=Sn. In systems of 1?:?2 compositions, calculated M···O distances are practically equal to the sum of covalent radii of M and O. Nonetheless, complexes with such composition are not formed in solid state. Total energy of the system which is lower than the sum of its components’ energies is not an indispensable condition for complex formation. The ³⁵Cl nuclear quadrupole resonance (NQR) frequencies and asymmetry parameters of the electric field gradient at the ³⁵Cl nuclei have been evaluated using the results of ab initio calculations.     

NQR and NMR study of hydrogen bonding interactions in anhydrous and monohydrated guanine cluster model: A computational study

In this paper extensive systematic computational study has been carried out to justify hydrogen bonding interactions and their influence on the oxygen, nitrogen and hydrogen NQR and NMR parameters of the anhydrous and monohydrated guanine crystal structures at two different levels, B3LYP and MP2, using 6-311++G** and D95** basis sets. These theoretical data have been compared with experimental NMR and NQR measurements. For further investigation, results of cluster calculation have been compared with that of a single molecule. Our theoretical NQR and NMR parameters of ¹⁷O, ¹⁵N and ²H atoms of anhydrous and monohydrated guanine exhibited extreme sensitivity to electron distribution around mentioned nuclei caused by cooperative influences of various types of hydrogen bonding interactions. Fortunately, our calculated isotropic shielding values and CS tensors for the ¹⁷O and ¹⁵N nuclei as well as obtained ¹⁴N-NQR parameters are in excellent agreement with experimental data. Therefore, we can undoubtedly conclude that for anhydrous and monohydrated guanine tetrameric clusters including intermolecular interactions, our theoretical estimates are in better agreement with observed experimental values than those in which these interactions have been ignored.     

Standardless,Automated Determination of Chlorine-35 by 35Cl Nuclear Magnetic Resonance

A robust, fully automated, walk-up method is reported to quantify chloride in samples using ³⁵Cl nuclear magnetic resonance. Minimal user input is required, no standards are acquired at the time of analysis; and the submission, acquisition, processing, and production of results are seamlessly integrated within existing software. The method demonstrated good linearity with R²?=?0.999 over three orders of magnitude of analyte concentration. The results were highly independent of analyte functionality, and the stability of instrument response was sufficient that analyses of additional standards were not required for a period of several months. At a nominal sample concentration of 10?mg/ml in D₂O at 400?MHz, detection and quantitation limits of 0.1 and 0.5% (w/w) were achieved in a 1-h analysis time. Robust methodology was achieved by applying a rigorous approach to method development and validation to determine and evaluate fully the time- and sample-dependent factors that affect quantitation in these measurements.