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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.

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.

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.

Alternative versions of gas-phase unimolecular decomposition of six isomeric trinitrotoluenes, in particular homolytic dissociation of Carom–NO2 and Carom–CH3 bonds, nitro–nitrite rearrangement, intramolecular hydrogen transfer from the methyl group to nitro group with formation of aci-trinitrotoluenes, and formation of various bicyclic intermediates, have been simulated at the B3LYP/6-31+G(2df,p) level of theory. Except for 3,4,5-trinitrotoluene, the most energetically favorable for all other examined trinitrotoluenes is intramolecular hydrogen transfer. 3,4,5-Trinitrotoluene preferentially decomposes via formation of [6 + 4]-bicyclic intermediates or homolytic dissociation of the Carom–NO2 bond.

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.

Alternative paths of gas-phase unimolecular decomposition of three nitrotoluenes and six dinitrotoluenes, in particular homolytic dissociation of the C–N bond, nitro–nitrite rearrangement, intramolecular hydrogen transfer from the methyl to nitro group with formation of isomeric aci-nitrotoluenes, and various paths involving formation of bicyclic intermediates, have been studied at the DFT B3LYP/6-31+G(2df,p) level of theory using GAUSSIAN 09 software package. The most energetically favorable path for o-nitrotoluene and 2,3-, 2,4-, 2,5-, and 2,6-dinitrotoluenes is the formation of aci-nitrotoluenes. The effect of the substrate structure on the competition between different mechanisms of these reactions has been analyzed.

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.

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

According to the results of ab initio quantum-chemical calculation 1-bis(dimethylamino)-4-bis(trimethylsilyl-2,3-diphosphabuta-1,3-diene exists as an E-isomer where electronic delocalization occurs involving donor dimethylamino and acceptor trimethylsilyl groups and also the multiple P = C bonds.

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.

We previously [1] studied the structure of 1,3,2benzodioxaphosphinan-4-ones by X-ray analysis, by IR spectroscopy, and by measuring their dipole moments. Regardless of the aggregate state, the phosphorus-containing heteroring with planar fragments exists preferentially in a flattened sofa conformation and that the exocyclic substituent occupies axial (N C O, NEt 2 ) or equatorial (Cl) position. In the present work we performed theoretical conformational analysis of 1,3,2-benzodioxaphosphinan-4-ones I IV by nonempirical B3LYP/6-31G(d) quantum-chemical calculations.