Dipole moments of phenyl,benzo, and benzo[b]thiopheno derivatives of thiophene; 1, 4-dithiin,and thianthrene and their sulfones

The dipole moments of a series of phenyl, benzo-, and benzo[b]thiopheno-derivatives of thiophene, 1,4-dithiin, and thianthrene have been determined. An increase in the dipole moments of the phenyl derivatives of thiophene with an increase in the number of phenyl groups is connected with the existence of conjugation between the thiophene and benzene rings, a quantitative evaluation of the nature of which is given. It is suggested that the structure of the 1, 4-dithiin ring is close to coplanar.     

Conformational analysis of aromatic derivatives of 2,3-dihydro-1H-1,5-benzodiazepine

The PMR spectra and dipole moments of some 2,4-disubstituted 2,3-dihydro-1H-1,5-benzodiazepines have been examined. It is shown that seven-membered rings with an aromatic or heterocyclic substituent in the 2-position have the boat configuration, the substitutent preferentially being equatorially oriented. It has been found that the changes in the chemical shifts and spin coupling constants for the protons of the CH-CH₂ fragment in the dihydrobenzodiazepine ring are mainly due to differences in the electronegativity of the substituents in the 2- and 4-positions. Some dipole moment vectors have been calculated for the dihydrobenzodiazepine ring.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1662–1666, December, 1984.     

Dipole moments. Structure and conformation of asymmetrically 4,5-substituted 1-(α-aroyloxyarylideneamino)-1,2,3-triazoles

The dipole moments of several asymmetrically 4,5-substituted 1-(α-aroyloxyarilideneamino)-1,2,3-triazoles, produced by oxidation of bis-aroylhydrazones of α-dicarbonyl compounds, were measured in benzene solution. The structure and the probable conformation of each of these compounds was determined by comparing their experimental and theoretical dipole moments. It has been found that when one of the substituents R₁ or R₂ is an aryl group, it is located at the 4-position of the triazole ring. Considering the conformation of the ester-imino function, it has been found to be the same as that of symmetrically substituted derivatives.     

Electron density distribution in heterocyclic systems with two vicinal nitrogen atoms. III. Dipole moments of some alkyl,aryl, and nitro pyrazole derivatives

Dipole moments of 13 alkyl and aryl derivatives of pyrazole are determined. It is found that fundamentally it is the pyrazole ring that determines the values of these dipole moments. The phenyl group behaves as a weak electron donor with respect to the pyrazole ring. It is shown that under the action of powerful electron-accepting substituents, such as the nitro group, the electron cloud of the pyrazole ring is polarized toward the electron acceptor.For Part II see [1].     

Electron density distribution in heterocyclic systems with two adjacent nitrogen atoms

Dipole moments found are compared with those calculated vectoran ially. Bis(3, 5-dimethylpyrazol-4-yl) has a constant dipole moment, which indicates inequality of nitrogen atoms in the pyrazole ring. Dipole moments of condensed pyrazolopyridines can be found by adding vectorially the dipole moments of pyridine and pyrazole. Involvement of a nitrogen atom and formation of two aromatic rings does not significantly alter the dipole moment of pyrazolo[2, 3-a]-pyridine as compared with pyrazole.For Part V see [1].     

Étude de la tautomérie des halogéno-triazoles-1,2,4 par determination expérimentale et théorique de leurs moments dipolaires

The dipole moments of sixteen 3(5)-halogeno-triazoles have been measured in dioxane at 25 ° C. Experimental dipole moments have been compared with those calculated by two semi-empirical methods CNDO/2 and PCILO, and with those computed vectorially. An energetic approach is also given.It is shown, in _N-unsubstituted 1,2,4-triazoles (for which three tautomeric forms, A, B and C are possible) that the predominating tautomer has a proton on the N1 atom and the electron-accepting substituent on the C3 atom.The effect of the introduction of an electron-accepting or donating substituent in position 3 and 5 of the triazole ring is discussed.     

Electron density distribution in heterocyclic systems with two adjacent nitrogen atoms

The dipole moments of 19 pyrazole derivatives are determined. Comparing measured dipole moments with those calculated by vector addition, differences in polarization of the pyrazole ring are considered as functions of the natures and positions of substituents. The inadequacy of a symmetrical structure for pyrazole, with a hydrogen linked to both nitrogens, is demonstrated. Comparison of experimentally determined dipole moments with those calculated by the vector method makes it possible to choose between tautomeric structures of 3,4-dibromopyrazole.For Part IV see [1].     

Liquid-Crystalline Order in the Phosphorus-Containing DenDrimers

The structure of phosphorus-containing dendrimers has been studied by IR spectroscopy and optical polarization microscopy. The repeating units of dendrimer molecules are mesogens. This property arises from the conjugation of the aromatic ring and the hydrazone group. An analysis of the IR spectra showed that, with an increase in the generation number, the width of the stretching vibration bands ν(PN) and ν(PO) increases. Difficulties in packing molecules of higher generations cause conformational diversity. The shape of the dendrimer molecules was determined by analyzing the increments of dipole moments. Additionally, the modeling of the stacking of repeating links was performed. The spherical model of molecules does not satisfy the experimental dipole moments of the dendrimers. The flat disk model is more suitable for explaining step changes in dipole moments. The liquid-crystalline ordering of dendrimers under the action of applied pressure was found. With simultaneous heating and uniaxial compression, optical anisotropy appears in dendrimers. It is associated with the formation of liquid-crystalline order. However, a thermodynamically stable liquid-crystalline phase is not formed in this case. Dendrimers most likely have disk-shaped molecules.     

Dipole moments,Kerr constants,and structure of oxides of substituted norbornenes

The molar Kerr constants and dipole moments at infinite dilution in CCl₄ have been measured for these compounds and also for dicyclopentadiene dioxide and the oxides of ethylene, propylene, and tetramethylethylene. The dipole moment indicates an exo-oxide structure for endo-cyanonorbornene, and this fact is used with the Kerr constants for endo-cyanonorbornene and ethylene oxide to calculate the axes of the polarizability ellipsoid for the oxide ring: b₁ (along the symmetry axis), b₂ (in plane of ring), and b₃ (perpendicular to plane of ring). The Kerr constants for propylene and tetramethylethylene oxides have been used to determine the anisotropy in the polarizability of the C-C bond adjoining the oxide ring. The results demonstrate an exo mode of oxidation of all substituted norbornenes and an exo-exo structure for dicyclopentadiene dioxide.     

Dipole moments and UV spectra of some two-ring cyclic sulfides

The dipole moments and UV spectra of 17 compounds of the 5,6-tetramethylene- and 5,6-trimethylenethiapyran series and their saturated analogs were measured. The dipole moments of the investigated compounds range from 1.2 to 2.0 D. The effect of the size of the saturated side ring and the position of the unsaturated bonds in the sulfur-containing heteroring on the dipole moments is demonstrated. The UV spectra of the compounds with, respectively, five- and six-membered saturated side rings are virtually identical. The position of the bands is determined primarily by the structure of the heteroring.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 744–747, June, 1978.     

Influence of heteroelement on dipole and quadrupole moments of a series of three-membered rings containing a second,third, fourth,or fifth-row atom: a theoretical investigation

The influence of heteroelements on the molecular dipole and traceless quadrupole moments of a series of twenty-two three-membered rings (1–22) was theoretically estimated employing levels of theory such as MP2, CCSD, and PBE1PBE in combination with standard Pople’s basis set. To an accurate evaluation of these properties, additional calculations on the optimized geometries were performed using the correlation-consistent cc-pVDZ and aug-cc-pVDZ basis sets on the three mentioned methods. In particular, the dipole and quadrupole moments from MP2 and CCSD approaches are comparable to each other for the studied molecules, while PBE1PBE calculations were significantly deviated compared to MP2 and CCSD levels. High level of theory and large basis sets seemed to be needed to obtain reliable electrical properties in the heterocycles containing heavy atoms. Results demonstrated that the dipole and quadrupole moments are strongly determined by the nature of the heteroatom into ring skeleton, and its magnitude depends on the polarity of C-heteroelement bond. Dipole moment of these molecules 1–22 showed a clear increase with the increase of electronegativity and the atomic size of heteroatom into ring skeleton. Then, high relative dipole moment was found for three-membered rings containing II, IIIA, VIA, and VIIA elements, which is associated to the high polarization of the C-heteroatom bond. A similar behavior was observed for the quadrupole moments of these three-membered rings.

     

Conformations of highly hindered aryl ethers: IX. Dipole moment evidence for an intramolecular donor-acceptor complex

In a search for evidence that a π cloud proximal halogen interaction is of importance to the mode of action of the thyroid hormones, the dipole moments of the 1'-naphthyl (I), (4.29 D), 4'-carboxymethylphenyl (II), (2.90 D), 2'-bromo4'-carboxymethylphenyl (III), (3.56 D), and methyl (IV), (3.24 D) ethers of 2,4dinitro-6-bromophenol were determined in benzene at 25 °C. The moments of (I), (II) and (III) are approximated best by those calculated for the twisted conformation in which the bromine closely approaches the face of the other ring. That of the naphthyl ether (I) can, however, be explained only by inclusion of an intramolecular electron donor-acceptor charge-transfer moment of 1.6 D directed from the π cloud of the naphthyl ring to the proximal nitro group of the other ring, or of 2.8 D to the proximal bromine of that ring. In the preferred conformation of the methyl ether (IV), the methoxy group is coplanar with the ring while the 2-nitro group is twisted 90° from coplanarity to accomodate it. A mesomeric moment of 2.3 D is estimated from this for the 2,4-dinitro-6-bromophenoxy moiety and is used in calculating the expected moments of the other ethers.     

Reaction of natural isoflavonoids and their analogs with hydroxylamine

Recyclization of the chromone ring in several natural isoflavonoids and their analogs by reaction with hydroxylamine was studied. It has been found that the most suitable base for carrying out the reaction is N-methylmorpholine. Several derivatives of 4-aryl-5-(2-hydroxyphenyl)isoxazole were synthesized. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 332–336, July–August, 2007.     

Determination of the ground- and excited-state dipole moments of 4’-(hexyloxy)-4-biphenylcarbonitrile and 4-isothiocyanatophenyl 4-pentylbicyclo [2,2,2] octane-1-carboxylate nematic liquid crystals and their mixtures

The dipole moments of the ground and excited states of 4′-(hexyloxy)-4-biphenylcarbonitrile and 4-isothiocyanatophenyl 4-pentylbicyclo [2.2.2] octane-1-carboxylate nematic liquid crystals and their mixtures prepared in chloroform and dichloromethane were studied at room temperature. The dipole moments of the ground states of the all samples were calculated according to the Guggenheim–Smith method. The dipole moments of their excited states were determined with the help of the Lippert equation by measuring the absorption and fluorescence spectra, solvent polarity and refractive index values. It was determined that dipole moments of the excited states were higher than those of the ground states. Moreover, the dipole moments of the ground and excited states of two nematic liquid crystals were also estimated by using molecular mechanic method (Gaussian09 program (DFT/B3LYP 6-31G(dp)). The results obtained are interpreted in detail.     

Electronic structure,UV spectra and reactivity of non-benzenoid systems by the INDO/S-CI method: Part II. Methylenecyclopropene and its derivatives

The electronic spectra, frontier molecular orbitals, charge distribution and dipole moments of nine compounds containing the cyclopropenyl ring have been studied by the all-valence-electrons INDO/S-CI method. The theoretical results agree fairly well with the experimental indications, where available. The σ-contribution to the net charge density on the ring as well as the μ_σ and s—p polarization contributions to the dipole moments are higher than in the fulvene derivatives, indicating greater participation of the smaller-ring system. The UV spectra of compounds containing two coupled rings correlate with those of the component frameworks, in agreement with previous semi-empirical calculations.     

极性分子键角与键偶极矩的关系

研究了基态极性分子的键角和键偶极矩之间的关系。我们采用原子偶极矩校正的Hirshfeld （ADCH）电荷来计算键偶极矩,利用电子的局域函数和键临界点处的局域函数值来分析键的电子结构。通过对IVA族（IVA = C,Si,Ge）、VA族（VA = N,P,As ）、VIA族（VIA = O,S,Se）和VIIA族（VIIA = F,Cl,Br）元素形成的系列共价型基态分子,以及环状基态分子的键角和键偶极矩数据进行分析,发现在键的电子结构类似的情况下,由于键偶极矩的排斥作用,这些分子的键角随键偶极矩的增加而增大。这一发现有助于加深我们对分子几何结构的认识。     

Dipole moments of thiophene analogs of chalcones and their vinylogs

The dipole moments of 25α, β unsaturated ketones of the thiophene series are measured in benzene at 25°, and their most probable coplanar conformations established. For the systems studied it is shown that, in the static state, the 2-thienyl group exhibits an electron-donating effect, greater than those of 2-furyl and phenyl. Introduction of electron-donating and electron-accepting substituents into the molecule of 1-(thienyl-2)-3-phenylpropenones as well as shift of the carbonyl group away from the aryl one towards the heterocyclic ring, leads in general to an increase in dipole moment. A linear relationship is found for the changes in dipole moment of isomeric thiophene ketones due to electron-donating substituents. Dipole moments of propen-3-ones correlate satisfactorily with Hammett σ parameters for substituents, and intermolecular distances.     

Rearrangement processes in the mass spectra of some 3,5-dimethylisoxazole derivatives

The mass spectra of isoxazole and some 3,5-dimethylisoxazole derivatives were investigated. Schemes for the formation of the principal rearranged ions are proposed on the basis of a study of the dissociative ionization of labeled compounds. Examples of the effect of electronic and steric factors on the probability of the existence of different channels for disintegration of the molecular ion are presented. It is shown that the formation of an ion with mass 82 during the dissociative ionization of a number of the investigated compounds occurs via different mechanisms as a function of the nature of the substituents in the 4 position of the isoxazole ring.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1336–1340, October, 1972.     

Efficient route to 2H-1,3-oxazines through ring expansion of isoxazoles by rhodium carbenoids

Studies related to the total synthesis of elisabethin C led to the discovery of a rhodium-catalyzed cascade sequence involving isoxazole ring expansion and a [4+3] cycloaddition. The scope of the isoxazole ring expansion was explored, resulting in the synthesis of a range of 2H-1,3-oxazines in 47-96% yield.     

The nature of the interaction between the phenyl and imidazole rings in narylimidazoles

The interaction between the imidazole ring and substituents in the benzene ring in some N-arylimidazoles is examined with the aid of dipole moments, UV spectra, ionization constants, and rate constants for the Menshutkin reaction.For part III, see [3]