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N-Benzylation of acylhydrazones of the hydroxybenzaldehyde series with 3,5-di-tert-butyl-4-hydroxybenzyl acetate was performed at room temperature in the absence of acid or base catalysts. Carboxamides do not react with 3,5-di-tert-butyl-4-hydroxybenzyl acetate under similar conditions. N-Benzylation of isoniazid and (diphenylphosphoryl)acetic acid hydrazones was shown to be an efficient method for the synthesis of new hybrid compounds containing moieties of biologically active acylhydrazones and sterically hindered phenols. N-Benzyl derivatives of isoniazid and (diphenylphosphoryl)acetic acid hydrazones containing a hydroxy group at the ortho position of the aromatic ring are formed as individual E isomers with respect to the C-N double bond.

The polarity and structure of tri(1- or 2-naphthyl)phosphines and their chalcogenides were determined by the methods of dipole moments, IR spectroscopy, and DFT quantum-chemical calculations at the B3PW91/6-311++G(df,p) level of theory. In solution, tri(1-naphthyl)phosphine prefers a single conformer with a gauche,gauche,gauche orientation of the substituents at the phosphorus. Tri(2-naphthyl)phosphine, as well as both phosphine chalcogenides exist as equilibrium mixtures of several forms with a propeller arrangement of the substituents and a cis or gauche orientation of the Csp2‒Csp2 and P=X (X = LEP, O, S, Se) bonds.

Conformational analysis of tris(4-methylphenyl)phosphine and its oxide, sulfide, and selenide has been performed by the dipole moment method and DFT quantum chemical calculations at the B3PW91/ 6-311++G(df,p) level of theory. The title compounds have been found to exist in solution as a single symmetrical conformer with gauche,gauche,gauche orientation of the substituents on the phosphorus atom with respect to the P=X bond (X = LEP, O, S, Se).

DFT quantum chemical calculations at the B3PW91/6-31G(d) level of theory have shown that the addition of secondary phosphine sulfides and phosphine selenides with alkyl, phenyl, and phenylalkyl substituents to pentyl vinyl and hexyl vinyl selenides follows a molecular mechanism against the Markovnikov rule through energetically favorable eight-membered transition state, leading to the formation of tertiary phosphine chalcogenides. Secondary phosphine selenides are more reactive than the corresponding phosphine sulfides.

Conformational analysis of Se-esters of diselenophosphinic acids has been performed and their polarities have been determined using the methods of dipole moments and quantum chemistry (DFT [B3PW91/6-311++G(df,p)]+CPCM). In solution, the studied compounds exist as an equilibrium of several conformers with staggered gauche and trans- or eclipsed cis-orientation of the substituents relative to the P=Se bond. The presence of eclipsed cis-conformations is explained by the formation of intramolecular H⋯Se bonds involving the hydrogen atom of the Se-alkyl(benzyl) or phenyl substituents at the phosphorus atom and the selenium atom of the P=Se group.

According to DFT calculations, hydrolysis of 1,1,1-trisubstituted hyposilatranes and hypogermatranes proceed in one stage and have lower activation energies than hydrolysis of the corresponding atranes and ocanes, and, unlike what is observed with the tricyclic and bicyclic analogs, the former reactions are characterized by positive Gibbs energies. The configuration of the hydrolysis products is stabilized by the transannular interactions N→X and O→X (X = Si, Ge) and intramolecular hydrogen bonding.

Conformational analysis of tris(3-methylphenyl)phosphine and its chalcogenides has been performed by methods of dipole moments, IR spectroscopy, and quantum chemistry [DFT B3PW91/6-31G(df,p)]. In solution, these compounds exist as an equilibrium of conformers with gauche- and cis-arrangement of the substituents at the phosphorus atom relative to the P=X bond (X = lone electron pair, O, S, Se).

According to DFT quantum chemical calculations, hydrolysis of 2,2-disubstituted silocanes and germocanes is characterized by lower energies of activation and slightly lower positive Gibbs energies than the hydrolysis of the corresponding silatranes and germatranes. The annular configuration of the hydrolysis products is stabilized by the transannular interaction N→X (X = Si, Ge) and intramolecular hydrogen bonding.

As shown by the dipole moment method and quantum chemical calculations, (arylcarbamoylmethyl) diphenylphosphine oxides and sulfides exist as equilibrium mixtures of several rotational isomers stabilized by H · · · X intramolecular hydrogen bonds (X = O, S). The most energetically favorable rotamer and its fraction have been determined for each compound.

Methods of preparation of complex phosphine selenide via the original Trofimov–Gusarova reaction are described. The results of the products conformational analysis by means of a set of physical methods (IR spectroscopy, dipole moments, and quantum chemical calculation) are presented.

Polarity of diselenophosphinates in benzene solution has been determined by second Debye method. We suggest that these compounds exist as a mixture of several conformers with cis and gauche arrangement of substituents at the phosphorus atom with respect to the P=Se bond.

As shown by the dipole moment method and quantum chemical calculations, 1-(furan-2-yl)-2-nitroethene and 1-nitro-2-(5-nitrofuran-2-yl)ethenes exist in solution as E-s-trans isomers while 1-bromo-2- (5-bromofuran-2-yl)-1-nitroethene and 1-bromo-1-nitro-2-(5-nitrofuran-2-yl)ethene have Z-s-cis configuration.

The polarity and conformational behavior of some phosphorus-containing enamino ketones have been determined by the dipole moment method, IR spectroscopy, and quantum chemical calculations. 3-[2-[(Diphenylphosphoryl)methyl]phenylamino]-1-phenylprop-2-en-1-one has been found to exist as the single Z isomer. 3-[2-(Diphenylphosphoryl)phenylamino]-1-phenylprop-2-en-1-one and 3-[2-(diphenylphosphorothioyl) phenylamino]-1-phenylprop-2-en-1-one exist in equilibrium between the Z and E isomers, the latter prevailing.

Conformations of 2-chloro-N-[2-(methylsulfanyl)phenyl]- and 2-(diphenylthiophosphoryl)-N-[2-(methylsulfanyl)phenyl]acetamides have been studied by the dipole moment method and quantum chemical calculations. 2-(Diphenylthiophosphoryl)-N-[2-(methylsulfanyl)phenyl]acetamide has been found to exist as an equilibrium mixture of two conformers with synclinal and anticlinal orientations of the $${C_{s{p^3}}} - {C_{s{p^2}}}$$ and P=S bonds. 2-Chloro-N-[2-(methylsulfanyl)phenyl]acetamide is represented by one preferred conformer.

The polarity and conformations of 2-aminophenyl-, 2-aminobenzyl-, and 2-nitrobenzyl(diphenyl)-phosphine oxides were studied by the dipole moment method, IR spectroscopy, and quantum chemical calculations. 2-Aminophenyl- and 2-aminobenzyl(diphenyl)phosphine oxides were found to exist preferentially as conformers with intramolecular hydrogen bond. 2-Nitrobenzyl(diphenyl)phosphine oxide is likely to be represented by equilibrium mixture of three conformers in which the phosphoryl and nitro groups are oriented syn or anti with respect to the $PC_{sp^3 } C_{sp^2 } $ fragment.

Conformational analysis of N-arylmaleimides and bis-maleimides was performed by the dipole moment method and quantum chemical calculations. The aromatic ring and heterocycle in N-arylmaleimides are turned with respect to each other through an angle of 42–44°, which excludes conjugation between these fragments. No conjugation exists between the dioxopyrrole rings in bridged bis-maleimides. The structure of the examined compounds is controlled by steric factors. Pronounced inductive effect of chlorine atoms in chloro-substituted bis-maleimides is responsible for their reduced dipole moments.

Diphosphorus-substituted isoxazole and 1,2,3-triazole were synthesized by a click chemistry method. Their polarity and structure were determined by the dipole moment method and quantum chemical calculations.

Polarity and structure of ethyl α-nitrocinnamates have been studied by means of dipole moments method and quantum-chemical calculations. These compounds exist in the form of Z-isomers in solution, that is, nitro group and benzene ring are cis-positioned.

Conformational analysis of 1,3,2-dioxaphospholan-2-yl 2,2,2-trifluoroacetate and 4,5-benzo-1,3,2-dioxaphosphol-2-yl 2,2,2-trifluoroacetate was carried out using the method of dipole moments and quantumchemical calculations (DFT B3LYP/6-31G*). Both compounds are found to exist as an axial conformer with preferably syn arrangement of the carbonyl group and the lone electron pair.

Polarity of 2-(1-methylbenzimidazol-2-yl)-1-phenyl- and -1,2-diphenyl-1-nitroethenes was determined and their structure was studied using electronic and 1H, 13C NMR spectroscopy, dipole moments measuring, XRD analysis, and quantum-chemical calculations. It was shown that the 2-(1-methylbenzimidazol-2-yl)-1-nitro-1-phenylethene has Z-configuration both in crystal and solution. The nitro group and benzimidazole substituent in its molecule are removed from the plane of the double bond. For 1,2-diphenyl-1-nitroethene E-structure is typical.

The structure of the new representatives of polyfunctional bromonitroalkenes, alkyl 2,3-dibromo-3-nitroacrylates, was examined by means of dipole moments, [B3LYP/6-31G(d)] quantum-chemical methods, and IR spectroscopy. They were found to have nontrivial Z-configuration in a solution.

The dipole moments of 6-thia-4,5: 6,7-dibenzo-1,3,2-dioxasilocines were determined experimentally and calculated at the DFT B3LYP/6-31G* level of theory and by the additivity scheme. The experimental and theoretical (DFT B3LYP/6-31G*) conformation analysis of eight-membered 1,3,2-dioxasilocines having planar fragments showed that these compounds in solution exist as boat-chair, boat-boat, or twist-boat conformers, depending on the presence of unsaturated planar fragment, nature of the heteroatom in position 6 of the eight-membered ring, and substituents on the silicon atom.

We have carried out the conformational analysis by the methods of dipole moments and quantum chemistry [DFT B3PW91/6-31G(d), B3PW91/6-311++G(3df, 3pd)] of bis[(4-chlorophenyl)ethyl]phosphine selenide (I) and bis-[(4-tert-butylphenyl)ethyl]phosphine selenide (II), which are promising initial materials for the synthesis of various organophosphoselenium compounds. Their structural formulas are presented in the scheme. The coeffi cients of the calculation equations and the experimental dipole moments of phosphine selenides I, II are compiled in Table 1. The most probable conformers of compounds I, II according to the quantum-chemical calculations are given below (hydrogen atoms are not shown). The energies, theoretical dipole moments and those computed using the vector-additive scheme for the conformational isomers of compounds I, II are presented in Table 2. In phosphine selenide I according to the data of B3PW91/6-31G(d) the energy minimum corresponds to conformer IА possessing a symmetric structure. However the calculation in an extended basis indicates the energy prevalence of conformer IB. Taking into consideration that the dipole moment values of conformer IB calculated in both bases is in better agreement with the experimental fi nding than those of conformer IA the results of B3PW91/6-311++G(3df,3pd) concerning the energy preference of conformer IB apparently should be regarded Table 1. Coeffi cients of calculation equations and experimental dipole moments of compounds I, II

The method of dipole moments and theoretical calculations (DFT B3LYP/6-31G*) were used for structural assessment of silatranes N[CH2(RMeC6H2)O]3SiR1 containing planar fragments in the six-membered semirings. They are endo structures with transannular N→Si interaction which involves, along with nitrogen and silicon, oxygen atoms adjacent to silicon.

Theoretical conformational analysis of 1-nitro- and 1-bromo-1-nitro-2-(trichloromethyl)ethenes dissolved in methylene chloride and benzene was carried out by the B3LYP/6-31G* method. The calculated structures of these compounds were found to nicely fit experiment: Both in the gas phase and in solution, 1-nitro-(2-trichloromethyl)ethene is an E isomer, while its bromine-containing analog is a Z isomer.

Molecular structure and vibrational spectra of 2-trichloromethyl(ethoxycarbonyl)-1-nitroethenes and 2-trichloromethyl(ethoxycarbonyl)-1-bromo-1-nitroethenes were calculated in terms of the density functional theory (B3LYP/6-31G*). The experimental FTIR spectra of these compounds in the range from 4000 to 400 cm−1 were interpreted in detail on the basis of the calculation data. 2-Substituted 1-nitro- and 1-bromo-1-nitroethenes were assigned the structure with trans orientation of the nitro and trichloromethyl (or ethoxycarbonyl) groups, and the ethoxycarbonyl derivatives were assumed to exist in equilibrium between s-cis and s-trans conformers.

Conformational analysis of 2-trichloromethyl(ethoxycarbonyl)-1-nitro-and 2-trichloromethyl-(ethoxycarbonyl)-1-bromo-1-nitroethenes was performed using the dipole moment method, IR spectroscopy, and DFT quantum-chemical calculations (B3LYP/6-31G*). The nitro and ester (or trichloromethyl) groups in the molecules of these compounds were found to occupy trans positions with respect to the double C=C bond, i.e., the nitroalkenes have E, and their bromine-containing analogs, Z configuration; the compounds having an ethoxycarbonyl group are characterized by s-cis orientation of the C=C and C=O bonds.

Conformational analysis of mono-and bis(dimethoxyphosphoryl)benzenes with substituents in the benzene ring was performed by the method of dipole moments, IR spectroscopy, and quantum-chemical calculations (DFT B3LYP/6-31G*). Comparison of all calculated and experimental data shows that the compounds studied exist as equilibrium mixtures of conformers with preferred gg orientation of the phosphoryl and methoxy groups.

According to X ray crystallographic analysis of compounds 1 and 2, both molecules have a chair con formation with the equatorial tert butyl substituent. Comparison of the geometric analysis of the rings of 1,3,2 dioxaphosphepines, phosphorinanes [2], and seven membered tert butylphosphonates with oxirane and thiirane planar fragments [3] indicates that the equatorial tert Bu group has no effect on the internal geometry of the ring. However, the lack of the “fro zen” NMR spectra of compounds 1 and 2 prevented us from drawing firm conclusions about their confor mations in solutions. In this context, of considerable interest is studying the effect of the tert butyl group on the geometry and conformations of the dioxaphosphepine ring, as well as analysis of experimental NMR data with the use of quantum chemical calculations. Quantum chemical calculations were performed by the hybrid B3PW91 density functional theory method [4, 5] with the use of the 6 31G(d) basis set. In all cases, all geometrical parameters of the molecules were optimized. The cor respondence of the found structures to PES minima was proved by all positive Hessian values. The chemi cal shifts and spin–spin coupling constants (SSCCs) were calculated by the GIAO method [6]. Calculations were performed with the Gaussian 09 program package at the Joint Supercomputer Center, Kazan Branch, Russian Academy of Sciences (http://wt.knc.ru).

The steric structure of 1,3,6,2-dioxazaphosphocanes and 1,3,6,2-dioxazasilocanes in solution was established by high-resolution 1H, 13C, and 31P NMR spectroscopy and PM3 calculations. It is shown that the preferred conformation of the eight-membered heterocycle is chair-chair (crown).

Experimental and theoretical study of reactions between dialkyl phosphites and tert-butylphosphaethyne revealed that the preferred reaction route resulted in formation of a phosphaalkene containing a fragment C=PP(O) including simultaneously a bicoordinate and tetracoordinate phosphorus.

Previously unknown 2-(1,2-dimethylindol-3-yl)-1-nitroethene was synthesized, and procedures for preparing 2-(1-methylbenzimidazol-2-yl)- and 2-(3-pyridyl)-1-nitroethens were improved. The structures of the products were determined by spectroscopic methods and from their dipole moments. According to single crystal X-ray diffraction data, the (E)-2-(1-methylbenzimidazol-2-yl)-1-nitroethene molecules are virtually planar and are packed in stacks in the crystal lattice, with appreciable stacking interaction.

A method was developed for preparing first representatives of phosphorylated nitrovinylindoles, bis(2-chloroethyl) 1-(indol-3-yl)- and bis(2-chloroethyl) 1-(1-alkylindol-3-yl)-2-nitroethenylphosphonates, and the structures of these compounds were studied. The spectroscopic data and results of dipole moment measurements show that the molecules have E configuration with s-cis arrangement of the multiple bond and phosphoryl group. X-ray studies have shown that the molecules of the first compound, having the E-s-cis form in the solid phase also, exist in the crystal in the form of enantiomeric pairs. They are involved in inter- molecular hydrogen bonds to form infinite chains.

The reaction of a stable two-coordinate phosphorus compound, 3,3-dimethyl-2-trimethylsiloxy-1-trimethylsilyl-1-phosphabut-1-ene, with diethyl phosphite was studied in terms of the density functional theory [DFT B3PW91/6-31G(d)]. A two-step mechanism of the reaction was established.

Under conditions of the phase transfer catalysis, acylation of (thio)phosphorylacetonitriles by (het)aroyl chlorides affords the Z-enol forms of C-acylation products in high yields. Their configurations were studied by IR spectroscopy, dipole moment measurements, and ab initio quantum-chemical calculations [B3LYP/6-31G(d)]. The C=C double bond and the phosphoryl or thiophosphoryl group have an s-cis arrangement. The possibility of strong intramolecular hydrogen bonding in these conformers is the governing factor responsible for the three-dimensional structures of the compounds under investigation. Derivatives of nicotinic acid existing in the individual form as zwitterions are the only exceptions.

Conformational analysis of bis(2-phenylalkyl)phosphine selenides was performed by the dipole moment method and quantum-chemical calculations. Bis(2-phenylpropyl)phosphine selenide was found to exist as a mixture of several conformers, the most energetically favorable of which being characterized by gauche (non-eclipsed) orientation of the P=Se and \(C_{sp^3 } - C_{sp^3 } \) bonds.

Conformational analysis of 4-methyl-2-trimethylsiloxy-1,3,2-dioxaphosphinane was performed by the dipole moment method and quantum-chemical calculations. The 1,3,2-dioxaphosphinane heteroring was found to adopt a chair conformation with equatorial orientation of the 4-methyl group and axial orientation of the irregular trimethylsiloxy substituent. The conformational equilibrium involves non-eclipsed gauche and trans conformers (the latter prevailing) interconvertible through rotation about the exocyclic P-O bond.

2-X-5,6-benzo-1,3,2-dioxaphosphinin-4-ones (X = N = C = O, Cl, NEt2), regardless of their aggregative state, prefer one and the same conformation (flattened sofa); the exocyclic substituent occupies either an axial (N = C = O, NEt2) or an equatorial (Cl) position.

Conformational analysis of 1-sila-4-phospha-2,5-cyclohexadienes was performed using the methods of dipole moments and quantum-chemicall calculations (DFT B3LYP/6-31G*). Irrespective of the degree of coordination of the phosphorus atom (3 or 4) the unsaturated six-membered heterocycles adopt the conformation of a flattened boat with the exocyclic phenyl group oriented perpendicular to the double bonds of the heterocycle. This conformation rules out the possibility of intramolecular transannular interaction between the phosphorus and silicon atoms.

A one-stage synthesis of 1-acyl-1-nitro-2-furyl(thienyl)ethenes was developed and structural assessment of the products was performed by means of 1H, IR, and UV spectroscopy and dipole moment measurements. The acetyl derivatives have Z configuration, and the benzoyl derivatives, E configuration. The UV and IR spectra, as well as the rather high dipole moments (μ ∼5-6 D) point to an essential contribution in the structures of dipolar forms.

A preparation method was developed for new representatives of halonitroenamines, 1-bromo-1-nitro-2-piperidino(cyclohexylamino)-2-phenylethenes. Both molecules possess E configuration and are of high polarity.

a Arbuzov Institute of Organic and Physical Chemistry, Kazan Research Center, Russian Academy of Sciences, ul. Arbuzova 8, Kazan, Tatarstan, 420088 Russia е-mail: mironov@iopc.ru b Kazan Federal University, Kazan, Tatarstan, Russia c Institute of Organic Chemistry, National Academy of Sciences of Ukraine, Kiev, Ukraine d Interinstitutional Supercoputer Center, Kazan Branch, Russian Academy of Sciences, Kazan, Tatarstan, Russia