Conformational analysis—XXVIII : Four-component equilibria in 1,3-dioxanes. Ring deformations and the chair-twist free energy difference

Four-component equilibria in substituted 1,3-dioxanes were applied to the determination of conformational energies not accessible by conventional equilibration, with the following conclusions: 1. The difference in free energy between the chair and twist forms of 2,2,trans - 4,6 - tetramethyl - 1,3 -dioxane is 7·4 kcal/mol. 2. Equatorial Me substituents at C-4,6 exert a palpable buttressing effect on the corresponding axial substituents. 3. Equatorial substituents at C-2 exert a similar buttressing effect on the geminal axial substituent. 4. The effect of equatorial t-Bu substitution or gem-dimethyl substitution at C-5 on conformational energy seems to be of minor importance. The more complex effects of equatorial 4-t-Bu substitution are discussed.     

Theoretical study of substituents effects on characteristics of resonance-assisted hydrogen bond in (Z)-(thionitrosomethylene)hydrazine and its derivatives in ground and electronic excited state

The molecular geometry, intramolecular hydrogen bond strength, vibrational frequencies, ¹H NMR chemical shift, and nuclear quadrupole resonance parameters of ¹⁴N, ³⁵S and ²H atoms and several well-established indices of aromaticity in (Z)-(thionitrosomethylene)hydrazine molecule and its derivatives were studied by density functional theory method. The results of calculations were obtained at B3LYP/6-311++G** level of approximation on model species, with the resonance-assisted hydrogen bonds. A set of simple and mostly common substituents having different properties in resonance effect according to values of substituents constants were chosen to simulate the influence of substitution in R position of title molecule on the quasi-delocalization and H-bonding. The following substituents have been taken into consideration: F, Cl, NO₂, OCH₃, OCF₃, SCH₃, SH, and OH. The excited-state properties of intramolecular hydrogen bonding in substituted systems have been investigated theoretically using the time-dependent density functional theory method. Also, the possible charge transfer and the topological properties of investigated molecule and its derivatives were studied by means of natural bond orbital and atoms in molecules (AIM) theory. The energy of the N–H···S interactions studied here was found medium in strength ( \( E_{\text{HB}}^{*} \)  = ?36.5 to ?45.3 kJ mol^?1). The electron density (ρ), Laplacian (?² ρ) properties and the total electron energy density (HC), estimated by AIM calculations, indicate that H···S bond possesses low ρ, positive ?² ρ and HC < 0 which are in agreement with partially covalent character of HB.     

Assessing the attractive/repulsive force balance in axial cyclohexane C–Hax···Yax contacts: A combined computational analysis in monosubstituted cyclohexanes

The interactions of axial substituents in monosubstituted cyclohexane rings are studied in this work using an array of different computational techniques. Additionally, the anomalous axial preference for some bulky substituents is related to stabilizing dispersion interactions. We find that the C–H_ax···Y_ax contacts for various substituents with distances ranging from 2 to ～5 Å may include attractive dispersion forces that can affect the conformational equilibrium; these forces co‐exist with Pauli repulsive forces effected by Y_ax group due to van der Waals sphere penetration. At distances between 2 and 3 Å stabilizing electron transfer interactions were calculated and the combination of natural bond orbital and QTAIM analysis showed that, in certain cases, Y_ax = ^tBu, C_ax–O or C_ax = O or S_ax = O or C_ax = S this interaction can be characterized as an improper H‐bond. DFT‐D3 and non‐covalent interactions calculations (NCIs) in cyclohexane derivatives with Y_ax = SiOR₃ including H_Yax···H_cy surfaces at distances ranging between 4 and 6 Å suggest that dispersion has a clear effect on the experimentally observed stabilization of the axial conformer. NCIs computed from the reduced density gradient help to visually identify and analyze these interactions. © 2016 Wiley Periodicals, Inc.     

Mechanism of the reaction of N-p-tosylsulphilimine and related compounds with thiophenolate ion

The reaction of alkyl aryl N-p-tosylsulphilimines with thiophenolate ion was found to afford quantitatively the sulphide that arises by an S_N2 like reaction on the carbon atom adjacent to the tri-valent sulphur atom. This reaction was also found to proceed smoothly with such compounds as sulphoxides and sulphones and sulphoxmanes. The kinetic study on the reaction between aryl methyl N-p-tosylsulphilimine with thiophenolate ion in DMF reveals that the reaction is of second order, namely, first order with respect to each thiophenolate ion and the sulphilimine. The enthalpy and entropy of activation for the reaction are ΔH^≠ = ?17· kcal/mol and ΔS^≠ = ?5·7 eu respectively. The effect of substituents in the reaction, p-XC₆H₄⁺(^?SO₂C₆H₄Y-p)CH₃ + p-ZC₆H₄SK is nicely correl with Hammett σ values giving ?_x = + 2·4, ?_y = + 1·2 and ?_z = ?1·8 respectively. Meanwhile, a marked steric retardation by a bulky alkyl group in alkyl phenyl N-p-tosylsulphilimine is observed. Furthermore, from the stereochemical study of the reaction using an optically active sec-octyl phenyl N-p-tosylsulphilimine with thiophenolate ion it is concluded that the reaction proceeds via a typical S_N2 process on α-carbon atom attached to the tri-valent sulphur atom.     

An excellent new resolving agent for the diastereomeric resolution of rac-mandelic acid

Chiral mandelic acid (S)-1, which is an important precursor for stereoselective transformations and a versatile intermediate for pharmaceuticals, was resolved with the Pope and Peachey method. Enantiopure 1-amino-3-phenoxypropan-2-ol (S)-2, a key intermediate for pharmaceuticals, was used to resolve rac-mandelic acid rac-1 successfully for the first time. The less soluble salt (S)-1·(S)-2·H₂O could be obtained in 77% yield and 98% de (E 75%) using (S)-2 and LiOH in water. The crystal structure of the less soluble salt (S)-1·(S)-2·H₂O showed that the water molecule played a key role in forming the crystals.     

Catalytic behavior of some copper(II) complexes with mixed ligands in the decomposition of hydrogen peroxide

A comparative study of the catalyzed decomposition of hydrogen peroxide using the following copper(II) complex salts, Cu(bipy)(S-threo)Cl · 3H₂O, Cu(phen)(S-threo)Cl · 2H₂O, Cu(bipy)(S-prol)Cl · 2H₂O and Cu(phen)(S-prol)Cl · 2H₂O has been made. Kinetic parameters were experimentally determined by the polarographic method at 25°C, pH 7.7 and constant ionic strength (μ = 0.1 M NaNO₃). The catalytic behavior of the chelate with 2,2′-bipyridine and S-prolinate was also studied at pH 6.5 and 8.5. The reactivity follows the sequence: [Cu(bipy)S-prol] > [Cu(phen)S-prol] > [Cu(bipy)S-threo] > [Cu(phen)S-threo]. Activation energies are very similar to each other. The pH-dependent exchange of the amino acid ligand with hydrogen peroxide seems to be a critical factor in the reaction pathway. Several reaction mechanisms are proposed.     

The influence of substituents on cooperativity between CH···<Emphasis Type="Italic">π</Emphasis> and N···H hydrogen bonds in a T-shaped configuration: X-benzene⊥(FH···pyrazine···HF) complexes as a working model

In the present work, the influence of substituents on cooperativity between CH···π and N···H hydrogen bonds is theoretically investigated in the T-shaped configuration of X-benzene⊥(FH···pyrazine···HF) complexes. The calculations are performed at MP2(FC)/6-311++G(d,p) level of theory. The results indicate that the absolute value of binding energy increases as the substituent changes from strong electron acceptor to strong electron donor. Moreover, cooperative and synergistic energies are computed in the complexes. The energetic data reveal a direct correlation between the electron-donating power of substituents and favorable influences of CH···π and N···H hydrogen bonds on each other. The results of AIM and NBO analyses show that the N···H hydrogen bond is strengthened by going from electron acceptor substituents to electron donor ones. It is also found that Hammett constants can be used to predict cooperative and synergistic effects between CH···π and N···H hydrogen bonds.     

Rotary friction,dipole moments,conformation and rigidity of polybutylisocyanate molecules in solution

Experimental data on the dependence of the rotatory diffusion coefficients and dipole moments on molecular weight and the theory of hydrodynamic properties and of the size of wormlike chains were used for determining the main conformational characteristics of the polyisocyanate chain S is the number of molecular units in a segment, λ is the length of the projection of the monomer unit on the axis of the molecule, and μ_o is the dipole moment of the monomer unit. The values of S and λ agree with those found previously by hydrodynamic methods. It was shown that the flat cis-structure of the polyisocyanate chain corresponds to values of λ = 2 × 10^?8cm andμ_o = 1·8D. Analysis of experimental data indicates that dimensions of “geometrical” and “electrical” segments in the PBIC chain are identical.     

Synergistic substrate and catalyst effects in the addition of trimethylsilyl cyanide to imines derived from lactic acid

Trimethylsilylcyanide was added to various imines derived from (2S)-ethyl lactate in the presence of Lewis acids to provide both syn- and anti- β-hydroxy-α-aminonitrile stereoisomers. Syn-products were found to be the major in most instances, however, anti-products were formed in good yield and selectivity in the presence of ZnI₂ & BF₃·OEt₂ and N-(−)-α-methylbenzyl substituents via double stereo differentiation.     

Resolution of 1-phenyl-2-(p-tolyl)ethylamine via diastereomeric salt formation

(S)-1-Phenyl-2-(p-tolyl)ethylamine (S)-1, used for the industrial scale resolution of chrysanthemic acids, was obtained via resolution of the racemate with the hemiphthalate of (S)-isopropylidene glycerol (R)-2. The maximum experimental efficiency [69% yield and >99% e.e. of (S)-1] was achieved by a simple precipitation of (S)-1·(R)-2 from the solution of the 1:1 diastereomeric salt mixture in 93/7 isopropanol/water at saturation of the more soluble (R)-1·(R)-2 salt. Such an experimental efficiency was consistent with 0.79 maximum theoretical resolvability, derived from the solubilities of the two diastereomeric salts, and with DSC data, which indicated that the (S)-1·(R)-2/(R)-1·(R)-2 system is a binary mixture exhibiting an eutectic with composition approximately corresponding to a 0.2 molar ratio of (S)-1·(R)-2.     

Theoretical conformational analysis of a simple sulphilimine model

The topomerization (bond rotation andS-pyramidal inversion) of a simple sulphilimine model, H₂SNH has been studied with the aid ofab initio SCF MO calculations. The highest rotation barrier occurs when the H₂SN moiety is planar, < HSN = 120 °. The maxima of the inversion crossections occur at the planar conformation for all rotation angles α as expected, however, the minima belong to different values when α is varied. The minimum energy path between the two lowest minima of the conformational energy surface consists of a pure inversion section and a section which is mostly rotation. The optimum values of the < HSN bond angles are significantly smaller than the corresponding < RSN bond angles of sulphilimines of bulkierR substituents.     

Cyclotetraveratrylene : Characterization and conformational properties

The preparation characterization of cyclotetraveratrylene (6) is described. Acid- catalyzed condensation of 3,4-dimethoxybenzyl alcohol or chloromethylation of bis(3,4- dimethoxyphenyL)methane both gave a mixture of cyclotriveratrylene (2) and 6 in approximately the proportion 5:1 respectively. The conformational mobility associated with the cyclododecatetraene ring of 6 was studied by variable temperature proton magnetic resonance spectroscopy over the temperature range 229–319K Activation parameters for the interconversion of “sofa” conformers 6A were obtained: F^≠_(T) 12sd8–13·7 (±0·3) kcal and S^≠ca - 11 (±2) eu. The large negative entropy term is interpreted in terms of a rigid, transitional conformer, possibly the crown form 6B.     

Can the substituent in the para position of anilide ion influence the N−···H–F → N–H···F− switching: a quantum chemical study

The effect of substituents in the para position of anilide ion (An) on the N^?···H–F → N–H···F^? switching in X–An–HF (X = H, Me, CHO, CN, NO, F, NO₂, OH and OMe) complexes was investigated by means of B3LYP and MP2 quantum chemical methods. To delve into the mechanistic details of the proton transfer process, potential energy curve and further geometrical parameters involved in H-bonding during the course of the proton transfer process were evaluated at the MP2/6-311++G(2d,2p) level of theory. The changes in H-bond strength because of variation of substituents were well accompanied by changes in formation energy of complexes, structural parameter, electron density, natural charge and charge transfer between subunits. For X = H, Me, CHO, CN, NO, F and NO₂ substituents, our results at MP2/6-311++G(2d,2p) level showed that the minimum energy structures correspond to the N···HF H-bonded complexes without proton transfer occurring. On the other hand, for electron-donating substituents OH and OMe, proton is transferred from HF to anilide ion and the minimum energy structures are HNH···F^? H-bonded complexes. The nature of HN^?···HF and HN–H···F^? interactions in complexes was characterized by means of atoms in molecules and natural bond orbital analyses.     

Unexpected retro-Michael reaction of (−)-(1′S,4aS,8aR)- and (+)-(1′S,4aR,8aS)-4a-ethyl-1-(1-phenylethyl)octahydroquinolin-7-ones

An unexpected retro-Michael reaction of (−)-(1′S,4aS,8aR)-and (+)-(1′S,4aR,8aS)-4a-ethyl-1-(1′-phenylethyl)octahydroquinolin-7-ones 1 and 2 is described. In addition, a diastereospecific intramolecular Michael reaction of 3·HCl and 4·HCl is reported.     

Enantiomeric hybrid high-temperature multiaxial ferroelectrics with a narrow bandgap and high piezoelectricity

Ferroelectric semiconductors have sparked growing attention in the field of optoelectronics, due to their unique ferroelectric photovoltaic effect. Recently, substantial efforts have been devoted to the development of ferroelectric semiconductors, including inorganic oxides, organic-inorganic hybrids, and metal-free perovskites. Nevertheless, reports of ferroelectric semiconductors with a bandgap of less than 2 eV have been scarce. Here, in combination with the incorporation of triiodide (I₃⁻) and the introduction of chiral cations, we successfully constructed a pair of enantiomeric organic-inorganic hybrid ferroelectric semiconductors, (S-1,2-DAP·I)₄·I₃·BiI₆ and (R-1,2-DAP·I)₄·I₃·BiI₆ (R/S-1,2-DAP = (R/S)-(–)-1,2-diaminopropane), which possess high-temperature multiaxial ferroelectric phase transition with an Aizu notation of 422F2(s) at 405 K, a narrow bandgap of 1.56 eV comparable to that of CH₃NH₃PbI₃ (∼1.5 eV), and an impressive piezoelectric response (piezoelectric coefficient, d₂₂ of 35 pC/N) on par with PVDF (polyvinylidene fluoride, 30 pC/N). With intriguing attributes, (S-1,2-DAP·I)₄·I₃·BiI₆ and (R-1,2-DAP·I)₄·I₃·BiI₆ exhibit great potential for application of self-power polarized-light detection and piezoelectric sensors.     

Experimental evidences for stereo-promoted intermolecular C-H···O hydrogen bonding in solution

The ¹H NMR data and the results of DFT quantum-chemical calculations indicate stereocontrolled formation of intermolecular C-H···O hydrogen bonds in aqueous solutions of L-(2S,3S)-2-(imidazol-1-yl)-3-methylpentan-1-ol.     

Resolution of 1-arylalkylamines with 3-O-hydrogen phthalate glucofuranose derivatives: role of steric bulk in a family of resolving agents

The development of three new acidic resolving agents which are hydrogen phthalates of 1,2:5,6-di-O-isopropylidene-α-d-glucofuranose 1, 1,2:5,6-di-O-cyclohexylidene-α-d-glucofuranose 2 and 1,2-O-cyclohexylidene-5,6-O-diphenylmethylidene-α-d-glucofuranose 3 is shown for the resolution of 1-arylalkylamines 7a–k. The salts between 1, 2 and (RS)-1-arylalkylamines 7a–k selectively crystallize 1·(S) 7a–j and 2·(S) 7a–h salts, allowing us to recover the corresponding bases (S) 7a–j and (S) 7a–h, respectively, in good yield and enantiomeric excess (73–95% ee). Whereas, the salts between 3 and (RS)-1-arylalkylamines 7a–c,g–i,k selectively crystallize 3·(S)-7a–c,g–i salts to recover the corresponding bases (S)-7a–c,g–i in poor enantiomeric excess (4–35% ee). The difference between the resolving ability of 1 and 2 for 1-arylalkylamines 7a–h is very slight, but there is considerable difference compared to ortho-substituted 1-arylalkylamines 7i and 7j. The role of substituents on a family of resolving agents 1, 2 and 3 is also discussed to interpret their resolving ability.     

The molecular structure of tetramethoxysilane in the gas phase,an electron diffraction study

The molecular structure of tetramethoxysilane was determined in the gas phase by electron diffraction. The molecule has S₄ symmetry, slightly flattened along the axis. The SiO bonds are shorter than in methylsilylether, demonstrating the effect of electronegative substituents on the Si atom. The geometrical parameters (r_a structure) are: Si-O bond 1.613 Å; C-O bond 1.414 Å; C-H bond 1.12 Å; O-Si-O angle bisected by S₄ axis 115.5°; Si-O-C angle 122.3°; O-C-H angle 111°; methoxyl torsional angle 64°; methyl torsional angle 60°.     

Structural and electronic properties of transition metal thiophosphates

From the viewpoint of metal coordination we examine the structural characteristics of several new members of transition metal thiophosphates (i.e., MPS phases with M = V, Nb, Ta), in which various ligands such as S²⁻, S²⁻₂, and phosphorus-sulfur polyanions P_nS^x−_m (1 ≤ n ≤ 4; 3 ≤ m ≤ 13; 2 ≤ x ≤ 6) provide either an octahedral or a bicapped prismatic coordination of the metal. Tight-binding band electronic structure calculations show that the low-lying acceptor orbitals responsible for lithium intercalation of thiophosphates are their d-block bands. This prediction is confirmed by our electrochemical lithium intercalation study which reveals that the reduction sites of thiophosphates are their metal cations. Molecular orbital calculations are carried out on vanadium compounds with extremely short interligand S···S contacts. The occurrence of such short contact distances is not caused by covalent bonding in the S···S contacts but by the small size of vanadium cations which forces its surrounding sulfur ligands to squeeze one another.     

Di­methyl­phenyl­sulfonium tri­fluoro­methane­sulfonate and methyl­di­phenyl­sulfonium tri­fluoro­methane­sulfonate

The bonding geometry of sulfur in the cations of the title compounds, C₈H₁₁S⁺·CF₃SO₃^? and C₁₃H₁₃S⁺·CF₃SO₃^?, respectively, is similar and is independent of the ratio of the Me/Ph substituents. As expected, in both cations, the S—Ph bonds are somewhat shorter than the S—Me bonds. In both crystal structures, the interaction between cations and anions is similar.