Conformational analysis of cinnamanilides

The conformational analysis of cinnamanilides has been carried out using IR spectroscopy. All the anilides studied were found to exist as equilibrium mixtures ofs-cis ands-trans forms in benzene. Thes-cis form was predominant over thes-trans in all the anilides except in thep-nitro anilide in which thes-trans form was predominant. The relative stabilities of the conformers were found to depend upon the electrostatic repulsions between the anilide nitrogen and the β-carbon atom in thes-trans form and those between the π-electrons of the C=O and C=C bonds in thes-cis form.     

Effect of aromatic ring anisotropy on the <Superscript>1</Superscript>H NMR shielding constants and conformational equilibrium of sterically strained aryl vinyl ethers

According to the ¹H and ¹³C NMR data and quantum-chemical calculations, phenyl vinyl ether exists mainly in the s-trans conformation which is characterized by concurrent p-π* interaction of the oxygen atom with both unsaturated fragments. Introduction of two methyl groups into the ortho positions of the benzene ring forces the latter to go out from the vinyloxy group plane, leading to loss of p-π* conjugation with the aromatic ring, enhancement of p-π* conjugation with the vinyl group, and transition of the molecule to s-cis conformation. The ¹H and ¹³C NMR data indicated that replacement of both o-methyl groups by tert-butyl makes the s-cis conformer sterically overcrowded even when the aromatic ring is oriented orthogonally with respect to the vinyl group; as a result, conformational equilibrium is displaced again toward s-trans rotamer.     

Dipole moments of some substituted benzaldehydes. Conformational preference of substituents ortho to the aldehyde group

The dipole moments of a number of substituted benzaldehydes are measured in benzene solution. The angle which the dipole axis of the CHO group makes with the axis of rotation of the group is determined. The observed moments of the ortho-substituted benzaldehydes are compared with the moments calculated for free rotation as well as fors-trans ands-cis orientations of the -CHO group.o-Fluorobenzaldehyde exists mostly in thes-trans conformation.o-Chloro-,o-bromo-ando-nitro-benzaldehydcs also exist in thes-trans conformation; their observed dipole moments are even lower than the values calculated fors-trans forms, indicating mutual induction of the ortho substituents. Though 2,5-dichlorobenzaldehyde is expected to have the same dipole moment as benzaldehyde, the observed moment is significantly lower due to mutual induction of the ortho substituents. 2,5-Dimethylbcnzaldehyde has, however, almost the same moment as benzaldehyde. The dipole moment ofo-methoxybcnzaldchyde is considerably higher than the values calculated for boths-cis ands-trans conformations. An explanation is given for this.o-Hydroxybenzaldehyde exists exclusively in thes-cis form due to internal H-bonding.     

Molecular and electronic structures and conformational analysis of derivatives of 9-nitroanthracene, anionic σ-complexes

Potassium 10-methoxy-9-nitroanthracenide was studied by X-ray diffraction analysis. The central ring of the anthracene fragment adopts an asymmetrically flattened boat conformation. The bond lengths in the C(Ar)−C(NO₂)−C(Ar) fragment are indicative of the presence of conjugation between the π-systems of the benzene rings and the nitro group owing to a substantial contribution of theaci form to the structure of the nitro group. Quantum-chemical calculations of anionic σ-complexes of 9-nitroanthracene derivatives were performed. In all cases, the central ring adopts two conformations with the pseudoaxial and pseudoequatorial orientations of the substituents at the saturated C(10) atom, respectively. The relative stability of the conformers and the factors determining the stability were considered. The minima on the potential energy surface have a flattened shape in spite of relatively high barriers to the conformational transition (2–4 kcal mol⁻¹). The deviation of the C(Ar)−C(Ar)−C(sp³)−C(Ar) torsion angle from the equilibrium value by ±20° causes an increase in the energy of the anion by less than 1 kcal mol⁻¹. The effect of the substituents on the charge distribution was considered. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 438–443, March, 1998.     

Dipole moments and molecular conformations ofO-vinyl- andO-ethylacetoximes in solutions

Dipole moments of the molecules ofO-vinyl- andO-ethylacetoximes in octane and THF were measured at different temperatures. In octane, the equilibrium mixture of stableO-vinylacetoxime conformers consists of forms with different polarity. Polarity of these conformers, which are due to rotation about the C−O and N−O bonds, is mainly determined by the relative position of the lone electron pairs of nitrogen and oxygen atoms. The fraction of the polar conformer increases as temperature increases, as well as on going from octane to THF. Saturation of the vinyl group in theO-vinylacetoxime molecule nearly halves the molecular dipole moment in the nonpolar medium, which radically differentiates this compound from vinyl ethers. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1685–1690, September, 1999.     

Long-range <Superscript>19</Superscript>F-<Superscript>1</Superscript>H spin-spin coupling as an indication of conformational equilibrium of fluoro-substituted aryl vinyl sulfides

Long-range ¹⁹F-¹H spin-spin coupling with participation of vinyl group protons, observed in the ¹H NMR spectra of fluoro-substituted aryl vinyl sulfides, indicates that these compounds exist as equilibrium mixtures of s-cis and s-trans rotational isomers.     

Kombinierte d-NMR- und LIS-Untersuchungen zum konformativen Verhalten von Formylmethylenthiopyranen

The rotational barriers ΔG ^≠ toE,Z- ands-cis, s-trans-isomerisation in formylmethylenthiopyranes are determined and discussed with regard to their dependence on substituent effects. Preferential conformers are distinguished by lanthanide induced shifts. Best fits between calculated and experimental shifts are obtained forE,s-trans andZ,s-cis isomers. The results indicate a nonbonding interaction between aldehyde oxygen and ring sulphur, favourings-cis conformation in case ofZ configuration.     

Through space spin-spin coupling <Superscript>19</Superscript>F-<Superscript>1</Superscript>H as the base for comparative analysis of conformational equilibrium in fluorine-substituted aryl vinyl selenides and sulfides

The analysis of long-range spin-spin coupling ¹⁹F-¹H and the other conformation-dependent parameters of ¹H NMR spectra shows that aryl vinyl selenides like aryl vinyl sulfides exist as mixtures of s-cis and s-trans rotational isomers. The combined data of ¹H and ¹³C NMR spectra reveal the increase in the torsional angle ϑ at the bond X-CH=CH₂ (X = S, Se) in selenides compared to sulfides due to diminished interaction energy of the unshared electron pairs of selenium with the π*-orbitals of the double bond as compared to analogous interaction in sulfides.     

Vibrational spectra,methyl torsional potential functions,internal rotational potential functions,and conformational properties of ethyl vinyl ether

The vibrational spectra of ethyl vinyl ether in both the fluid and solid states have been recorded from 20 to 3500 cm^?1. The 33 fundamental modes of vibration have been assigned. Three rotational isomers have been observed and their structures have been determined. The most stable conformer, s-cis/s-trans, is planar and of C_s symmetry. The two less stable rotamers, skew/s-trans and skew/gauche, are non-planar and of C_i molecular symmetry. The barrier to internal rotation of the methyl rotor has been determined for each conformation; these barriers are 3.43 kcal mol^?1 (s-cis/s-trans), 3.35 kcal mol^?1 (skew/s-trans) and 3.19 kcal mol^?1 (skew/gauche). A potential function for each of the two asymmetric internal rotations has been calculated and barriers to conformer interconversion have been determined. From the asymmetric potential function calculations, ΔH, the enthalpy difference between the conformers, has been determined. The s-cis/s-trans conformer is 1.87 kcal mol^?1 more stable than the skew/s-trans conformer; the skew/s-trans conformer is more stable than the skew/gauche conformer by 1.10 kcal mol^?1. The energetics of conformer interconversion and methyl internal rotation have been described in terms of molecular geometry and non-bonded interactions. These results are compared to those found in other alkyl vinyl and dialkyl ethers.     

Discrimination of s-cis/s-trans conformers of jet-cooled methyl cinnamate by population labelling spectroscopy

The S₁−S₀ electronic spectrum of methyl cinnamate in a supersonic jet has been investigated to discriminate the transitions of the s-cis/s-trans conformers. Population labelling spectroscopy was applied to the conformer discrimination, and vibronic bands belonging to each conformer were identified. The relative population was estimated from the fluorescence quantum yields obtained by lifetime measurements. It was found that both conformers exist almost equally in a supersonic jet. The conformer identification of the vibronic bands was carried out based on the difference of the red-shift of their hydrogen-bonded complexes with methanol.     

Structure and Properties of 2,2-Dibromovinyl Trifluoromethyl Ketone

It was established by IR spectroscopy and quantum-chemical calculations along nonempirical DFT method in B3LYP version with the basis set 6-311 G(d,p) that 2,2-dibromovinyl trifluoromethyl ketone consisted of a mixture of s-cis planar conformer and s-trans-form deviating from a plane by 13°, whereas the s-cis-form is more energetically stable than the s-trans one (E -5.07 kcal mol^{- 1}). Also in 2,2-dibromovinyl methyl ketone the planar s-cis conformer is more stable. Chlorine-containing analogs, 2,2-dichlorovinyl trifluoromethyl ketone and 2,2-dichlorovinyl methyl ketone, are more stable in the planar s-trans-conformation. Charge distribution and polarization in the dibromovinyl ketones are analogous to those in dichlorovinyl ketones in agreement with the established reactivity of dibromovinyl trifluoromethyl ketone. By reaction of 2,2-dibromovinyl trifluoromethyl ketone with 2,4-dinitrophenyl-, alkylhydrazines, N,N-dimethylhydrazine, N,N-, N,O-, N,S-binucleophiles were respectively obtained hydrazone, derivatives of pyrazole, imidazole, oxazole, and 1,3-thiazine containing a trifluoromethyl group.     

The Thermal Expansion of Wood Cellulose Crystals

We have investigated tension wood cellulose obtained from Populus maximowiczii using X-ray diffraction at temperatures from room temperature to 250 °C. Three equatorial and one meridional d-spacings showed a gradual linear increase with increasing temperature. For temperatures above 180 °C, however, the equatorial d-spacing increased dramatically. Thus, the linear and volume thermal expansion coefficients (TECs) below 180 °C were determined from the d-spacings. The linear TECs of the a-, b-, and c-axes were: α _a = 13.6 × 10⁻⁵ °C⁻¹, α _b = −3.0× 10⁻⁵ °C⁻¹, and α _c =0.6× 10⁻⁵ °C⁻¹, respectively, and the volume TEC was β = 11.1× 10⁻⁵ °C⁻¹. The anisotropic thermal expansion in the three coordinate directions was closely related to the crystal structure of the wood cellulose, and it governed the macroscopic thermal behavior of solid wood.     

Spectrophotometric and Potentiometric Studies on the Binding Abilities of Two Novel Tripodal Imine-Phenol Ligands Towards Al(III) and Ga(III)

The aqueous coordination behavior of two novel tripodal imine-phenol ligands, cis,cis-1,3,5-tris{(2-hydroxybenzilidene)aminomethyl}cyclohexane (TMACHSAL, L¹) and cis,cis-1,3,5-tris{[(2-hydroxyphenyl)ethylidene]aminomethyl}cyclohexane (Me₃- TMACHSAL, L²) with Al³⁺ and Ga³⁺ has been investigated at an ionic strength of 0.1 mol⋅dm⁻³ KCl and 25±1 °C by potentiometric and spectrophotometric methods. Both ligands formed various monomeric metal complex species MLH₃, MLH₂, MLH, ML and MLH₋₁ with Ga(III); and MLH₃, ML and MLH₋₁ with Al(III). The Ga(III) complexes showed higher thermodynamic stability than the Al(III) complexes. Semi-empirical PM6 calculations along with TDDFT/B3LYP/3-21G calculations have been performed to complement the experimental measurements. The calculated structure of the metal complexes predicted a distorted octahedral geometry where favorable ring-flipping from the equatorial conformation in uncomplexed ligands to the axial conformation was observed upon chelation.     

The molecular conformation of butyl acrylate – A vibrational spectroscopy and computational study

Potential energy curves allow us to probe the flexibility of butyl acrylate molecule. We found two local minima belonging to C_s symmetry for s-cis and s-trans conformations. The optimized geometries at RHF and DFT using extended basis set are in good agreement with electron diffraction data of methyl acrylate, and the s-cis is the most stable form. Ab initio calculations of harmonic frequencies at the fully optimized geometries of the planar s-cis and s-trans conformers have been performed at the DFT//B3LYP/6-311+G** level of theory. Scaled harmonic frequencies and potential energy distribution are used for the assignment of the experimental IR and Raman bands. We noticed an acceptable qualitative agreement between the experimental and the computed spectra.     

Polyethylene oxide—polysiloxane branched copolymers and networks

The hydrosilylation of vinyl methyl and divinyl ethers of oligoethylene glycols with polyhydridosiloxanes in the presence of chloroplatinic acid is accompanied by side processes, namely, polymerization of vinyl ethers and homodehydrocondensation of polyhydridosiloxanes. The electrical conductivity of ∼1M solutions of lithium triflate or bis(trifluoromethylsulfonyl) imide in the resulting hydrosilylation products is ∼10⁻⁵ S cm⁻¹.     

High Level Expression of an Acid-Stable Phytase from <Emphasis Type="Italic">Citrobacter freundii</Emphasis> in <Emphasis Type="Italic">Pichia pastoris</Emphasis>

To obtain a high level expression of phytase with favorable characteristics, a codon-optimized phytase gene from Citrobacter freundii was synthesized and transferred into Pichia pastoris. Small-scale expression experiments and activity assays were used to screen positive colonies. After purified by Ni²⁺–NTA agarose affinity column, the characterizations of the recombinant phytase were determined. The recombinant phytase (r-phyC) had two distinct pH optima at 2.5 and 4.5 and an optimal temperature at 50 °C. It retained more than 80% activity after being incubated under various buffer (pH 1.5–8.0) at 37 °C for 1 h. The specific activity, Km, and Vmax values of r-phyC for sodium phytate were 2,072 ± 18 U mg⁻¹, 0.52 ± 0.04 mM, and 2,380 ± 84 U mg⁻¹ min⁻¹, respectively. The enzyme activity was significantly improved by 1 mM of K⁺, Ca²⁺, and Mg²⁺. These characteristics contribute to its potential application in feed industry.     

An ab initio Molecular Orbital Study of the Conformational Properties of all-( Z )-Cyclododeca-1,4,7,10-tetraene

 Ab initio HF/6-31G^* and MP2/6-31G^*//HF/6-31G^* methods were used to calculate the structure optimization and conformational interconversion pathways for all-(Z )-cyclododeca-1,4,7,10-tetraene. This compound adopts the symmetrical crown (C _4v) conformation. Ring inversion takes place via symmetrical intermediates, such as boat-chair (BC, C _s) and twist (C _2h) conformers and requires about 22.3 kJ · mol⁻¹. The calculated strain energies for BC and twist conformers are 5.9 and 13.5 kJ · mol⁻¹. The results of semiempirical AM1 calculations for structural parameters and relative energies of the important geometries of the title compound are in good agreement with the results of ab initio methods.     

Cross-linking epoxide resins with hydrolysates of chrome-tanned leather waste

Differential scanning calorimetry was employed to investigate the reaction of diglycidyl ethers of bisphenol A (DGEBA) of mean molecular mass 348–480 Da, with collagen hydrolysate of chrome-tanned leather waste in a solvent-free environment. The reaction leads to biodegradable polymers that might facilitate recycling of plastic parts in products of the automotive and/or aeronautics industry provided with protective films on this basis. The reaction proceeds in a temperature interval of 205–220°C, at temperatures approx. 30–40°C below temperature of thermal degradation of collagen hydrolysate. The found value of reaction enthalpy, 519.19 J g⁻¹ (= 101.24 kJ mol⁻¹ of epoxide groups) corresponds with currently found enthalpy values of the reaction of oxirane ring with amino groups. Reaction heat depends on the composition of reaction mixture (or on mass fraction of diglycidyl ethers in the reaction mixture); proving the dependence of kinetic parameters of the reaction (Arrhenius pre-exponential factor A (min⁻¹) and activation energy E _a (kJ mol⁻¹)) did not succeed. Obtained values of kinetic parameters are on a level corresponding to the assumption that reaction kinetics is determined by diffusion.     

The Potential Energies of Cohesion of a Crystalline Organic Enantiomer and the Racemate; on the Energy for the Liquid Racemate [1]

Summary. The cohesion potential energy of the crystal of one enantiomer of ethyl 3-cyano-3-(3,4-dimethyloxyphenyl)-2,2,4-trimethylpentanoate, −47.7 ± 0.1 kJ mol⁻¹ (0–90°C), was found out from the heat of sublimation (123.2 ± 5.1 kJ mol⁻¹, 78.6°C) and the kinetic energies for the gas phase and the crystal. It was found that the entropy function of Debye’s theory of solids mathematically agreed with the vibrational entropy of the gas (variationally obtained), allowing to disclose the vibrational energy using the Debye energy function (E _vib 835.0 kJ mol⁻¹ (78.6°C), E ⁰ included). E _kin for the crystal (771.1 kJ mol⁻¹ (78.6°C)) was obtained by Debye’s theory with the experimental heat capacity. The cohesion energy represented a moderate part of the sublimation energy. The cohesion energy of the racemic crystal, −44.2 kJ mol⁻¹, was obtained by the heat of formation of the crystal in the solid state (3.0 kJ mol⁻¹, 83.3°C) and E _kin for the crystal (by Debye’s theory). The decrease in cohesion on formation of the crystal accounted for the energy of formation. The change in potential energy on liquefaction of the racemate from the gas state was disclosed obtaining added-up E _{vib + rot} for the liquid in the way as to E _vib for the gas, the Debye entropy function being increasedly suited for the liquid (E _{vib + rot} 763.4 kJ mol⁻¹ (115.4°C)). Positive ΔE _pot, 13.0 kJ mol⁻¹, arised from the increase in electronic energy (Δ _l ν_mean − 154.3 cm⁻¹, by the dielectric nature of the liquid), added to the cohesion energy.     

The Potential Energies of Cohesion of a Crystalline Organic Enantiomer and the Racemate; on the Energy for the Liquid Racemate [1]

The cohesion potential energy of the crystal of one enantiomer of ethyl 3-cyano-3-(3,4-dimethyloxyphenyl)-2,2,4-trimethylpentanoate, −47.7 ± 0.1 kJ mol⁻¹ (0–90°C), was found out from the heat of sublimation (123.2 ± 5.1 kJ mol⁻¹, 78.6°C) and the kinetic energies for the gas phase and the crystal. It was found that the entropy function of Debye’s theory of solids mathematically agreed with the vibrational entropy of the gas (variationally obtained), allowing to disclose the vibrational energy using the Debye energy function (E _vib 835.0 kJ mol⁻¹ (78.6°C), E ⁰ included). E _kin for the crystal (771.1 kJ mol⁻¹ (78.6°C)) was obtained by Debye’s theory with the experimental heat capacity. The cohesion energy represented a moderate part of the sublimation energy. The cohesion energy of the racemic crystal, −44.2 kJ mol⁻¹, was obtained by the heat of formation of the crystal in the solid state (3.0 kJ mol⁻¹, 83.3°C) and E _kin for the crystal (by Debye’s theory). The decrease in cohesion on formation of the crystal accounted for the energy of formation. The change in potential energy on liquefaction of the racemate from the gas state was disclosed obtaining added-up E _{vib + rot} for the liquid in the way as to E _vib for the gas, the Debye entropy function being increasedly suited for the liquid (E _{vib + rot} 763.4 kJ mol⁻¹ (115.4°C)). Positive ΔE _pot, 13.0 kJ mol⁻¹, arised from the increase in electronic energy (Δ _l ν_mean − 154.3 cm⁻¹, by the dielectric nature of the liquid), added to the cohesion energy.