Hindered rotation around the aryl-to-nitrogen bond of n-acetyl,n-ethoxycarbonylmethyl-2-amino, 5-nitrothiophen

Two stereoisomers of the title compound are observed by H NMR at 10°. Their spectra coalesce at higher temperature (10°-90°). The equilibrium and rate constants K and k, strongly dependent on the solvent used (1,4-dioxane, tetrahydrofuran, acetone, chloroform); typical values for these parameters and the related thermodynamic functions are: K(25°)= 0.170; k(25°)=23.2s^?1; ΔH_R and ΔH^≠=4.94 and 17.9 kcal.mol.^?1; ΔS_R and ΔS^≠ =13.1 and 7.7 e.u, in a 0.2 molar solution in 1,4-dioxane. The two isomers are shown to result from a hindered rotation around the aryl-to-nitrogen bond, presumably due to a direct resonance effect between the amide and nitro groups. The more abundant isomer was assigned a planar molecular structure in which the O atom of the amide group is close to the S atom of the thiophen ring, presumably on account of an electrostatic interaction between these two atoms which bear partial electrical charges of opposite sign.     

Preparation and properties of polyesters from diphenylmethane-4,4′-di(methylthiopropionic acid) and aliphatic diols

The new linear polyesters containing sulfur in the main chain were obtained by melt polycondensation of diphenylmethane-4,4′-di(methylthiopropionic acid) with ethanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-propanediol, 1,3-butanediol, and 2,2′-oxydiethanol. Low-molecular weights, low-softening temperatures and, very good solubility in organic solvents are their characteristics. The structure of all polyesters was determined by elemental analysis, FT-IR and ¹H-NMR spectroscopy, and x-ray diffraction analysis. The thermal behavior of these polymers was examined by differential thermal analysis (DTA), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The kinetics of polyesters formation by uncatalyzed melt polycondensation was studied in a model system: diphenylmethane-4,4′-di(methylthiopropionic acid) and 1,4-butanediol or 2,2′-oxydiethanol at 150, 160, and 170°C. Reaction rate constants (k₃) and activation parameters (ΔG^≠, ΔH^≠, ΔS^≠) from carboxyl group loss were determined using classical kinetic methods. © 1997 John Wiley & Sons, Inc.     

The solvation of L-serine in mixtures of water with some aprotic solvents at 298.15 K

The integral enthalpies of solution Δ_sol H ^m of L-serine in mixtures of water with acetonitrile, 1,4-dioxane, dimethylsulfoxide (DMSO), and acetone were measured by solution calorimetry at organic component concentrations up to 0.31 mole fractions. The standard enthalpies of solution (Δ_sol H°), transfer (Δ_tr H°), and solvation (Δ_solv H°) of L-serine from water into mixed solvents were calculated. The dependences of Δ_sol H°, Δ_solv H°, and Δ_tr H° on the composition of aqueous-organic solvents contained extrema. The calculated enthalpy coefficients of pair interactions of the amino acid with cosolvent molecules were positive and increased in the series acetonitrile, 1,4-dioxane, DMSO, acetone. The results obtained were interpreted from the point of view of various types of interactions in solutions and the influence of the nature of organic solvents on the thermochemical characteristics of solutions.     

1H NMR Study of Hindered Internal Rotation of Tetramethylthiuram Disulfide in Binary Dimethyl Sulfoxide‐Chloroform Mixtures

Hindered internal rotation about the C‐N single bonds joining the thiuram disulfide was studied by ¹H NMR complete line‐shaped analysis in different dimethyl sulfoxide‐chloroform (DMSO‐CDCl₃) mixtures. From the temperature dependence of methyls proton spectra, activation parameters (E_a, ΔH^≠, ΔS^≠, and ΔG^≠) were obtained. The Arrhenius plots showed a distinct isokinetic temperature at about 35 °C at which the exchange rate is more or less independent of the solvent composition. The resulting ΔH^≠ against TΔS^≠ plot showed a firmly good linear correlation, indicating the existence of an enthalpy‐entropy composition in an exchange process.     

Bistable or Oscillating State Depending on Station and Temperature in Three‐Station Glycorotaxane Molecular Machines

High‐yield, straightforward synthesis of two‐ and three‐station [2]rotaxane molecular machines based on an anilinium, a triazolium, and a mono‐ or disubstituted pyridinium amide station is reported. In the case of the pH‐sensitive two‐station molecular machines, large‐amplitude movement of the macrocycle occurred. However, the presence of an intermediate third station led, after deprotonation of the anilinium station, and depending on the substitution of the pyridinium amide, either to exclusive localization of the macrocycle around the triazolium station or to oscillatory shuttling of the macrocycle between the triazolium and monosubstituted pyridinium amide station. Variable‐temperature ¹H NMR investigation of the oscillating system was performed in CD₂Cl₂. The exchange between the two stations proved to be fast on the NMR timescale for all considered temperatures (298–193 K). Interestingly, decreasing the temperature displaced the equilibrium between the two translational isomers until a unique location of the macrocycle around the monosubstituted pyridinium amide station was reached. Thermodynamic constants K were evaluated at each temperature: the thermodynamic parameters ΔH and ΔS were extracted from a Van′t Hoff plot, and provided the Gibbs energy ΔG. Arrhenius and Eyring plots afforded kinetic parameters, namely, energies of activation E_a, enthalpies of activation ΔH^≠, and entropies of activation ΔS^≠. The ΔG values deduced from kinetic parameters match very well with the ΔG values determined from thermodynamic parameters. In addition, whereas signal coalescence of pyridinium hydrogen atoms located next to the amide bond was observed at 205 K in the oscillating rotaxane and at 203 K in the two‐station rotaxane with a unique location of the macrocycle around the pyridinium amide, no separation of ¹H NMR signals of the considered hydrogen atoms was seen in the corresponding nonencapsulated thread. It is suggested that the macrocycle acts as a molecular brake for the rotation of the pyridinium–amide bond when it interacts by hydrogen bonding with both the amide NH and the pyridinium hydrogen atoms at the same time.     

A DNMR study on the ring inversion of oxazolidines

Ring inversion of eight substituted 2-phenyl-4, 4-dimethyloxazolidines in o-dichlorobenzene-d₄ was studied by ¹H DNMR. Very high inversion barriers (ΔG_o^≠ = 86.7–93.4 kJ·mol^?1) were found for these oxazolidine rings. The magnitude of the inversion barrier is dependent on the polarity of the substituent on the phenyl group. A linear correlation is present between the ΔG_o^≠ of the inversion and the substituent constant, σ+, of the substituent.     

Determination of ΔH≠ and ΔS≠ by simultaneous 1H and 13C dynamic n.m.r. studies: Importance of the accuracy of temperature measurement

From ΔG_Tc^≠ values obtained by ¹H and ¹³C dynamic nuclear magnetic resonance studies of the same dynamic process, it is possible to estimate ΔH^≠ and ΔS^≠. Nevertheless, the accuracy of the temperature measurement is a factor which limits the applicability of this method. A very simple procedure for calibrating the usual temperature sensors is described, which can be applied to all types of n.m.r. probes. By the use of this procedure it is possible to measure coalescence temperatures in ¹H and ¹³C n.m.r. with such an accuracy that ΔS^≠ can be effectively determined from the difference between ΔG_Tc^≠ values.     

Ruthenium(III)-catalyzed mechanistic studies of oxidation of benzhydrols by sodium N-chloro-p-toluenesulfonamide in HCl medium

The kinetics of oxidation of benzhydrol and its p-substituted derivatives (YBH, where Y=H, Cl, Br, NO₂, CH₃, and OCH₃) by sodium N-chloro-p-toluenesulfonamide or chloramine-T (CAT), catalyzed by ruthenium(III) chloride, in the presence of hydrochloric acid in 30% (v/v) MeOH medium has been studied at 35°C. The reaction rate shows a first-order dependence on [CAT]_O and a fractional-order each on [ YBH]_O, [Ru(III)], and [H⁺]. The reaction also has a negative fractional-order (−0.35) behavior in the reduction product of CAT, p-toluenesulfonamide (PTS). The increase in MeOH content of the solvent medium retards the rate. The variation of ionic strength of the medium has negligible effect on the rate. Rate studies in D₂O medium show that the solvent isotope effect, k′H₂O/k′D₂O, is equal to 0.60. Proton inventory studies have been made in H₂O(SINGLEBOND)D₂O mixtures. The rates correlate satisfactorily with Hammett σ relationship. The LFE relationship plot is biphasic and the reaction constant ρ=−2.3 for electron donating groups and ρ=−0.32 for electron withdrawing groups at 35°C. Activation parameters ΔH^≠, ΔS^≠, and ΔG^≠ have been calculated. The parameters, ΔH^≠ and ΔS^≠, are linearly related with an isokinetic temperature β=334 K indicating enthalpy as a controlling factor. A mechanism consistent with the observed kinetics has been proposed. © 1997 John Wiley & Sons, Inc.     

Die Konformativen Umwandlungen des Ungesättigten Siebenringes in 4.5.6-Trithia-1.2-Benzocycloheptenen-(1) Konformative Beweglichkeit Flexibler Ringsysteme—XVI. Untersuchungen mit Hilfe Der Protonenresonanzspektroskopie

The conformational equilibria and conversions of 4.5.6-trithia-1.2-benzocycloheptene-(1) ( 1 ) and the 3′.6′-dimethoxy-, 3′.6′-dimethyl- and 3′.6′-diphenyl- derivatives ( 2, 3 and 4 ) were investigated by NMR spectroscopy. Solutions of these substances are equilibrium mixtures of two conformers, one presumably having a chair form and the other a boat form. The free enthalpy of the boat conformer ΔG_B is dependent on the size of the substituents (R) in the 3′ and 6′ positions. The ΔG_B values for R = H, OCH₃, C₆H₅ and CH₃ are 1,03, 0,82, 0,50 and ?0,19 kcal/moles, respectively. By slow crystallization one conformer of the substituted trithiabenzocycloheptenes may be obtained in a pure crystalline form. The dimethoxy derivative crystallizes in the chair form, whereas the dimethyl and the diphenyl derivatives crystallize in the boat form. After dissolving the crystals, the conformational equilibrium is restored; at 0°C the half-lifes range from 2 to 15 minutes. By means of the temperature dependence of the NMR spectra two different types of conformational changes may be distinguished experimentally: the slower one is assigned to the inversion of the seven membered ring and the faster one to its pseudorotation. The free enthalpy of activation ΔG_v^≠ of the inversion was determined for 4.5.6-trithia-1.2-benzocycloheptene-(1) by the ‘line-shape’ method and for the diphenyl derivative by the ‘equilibration’ method. Both methods were applied to the other derivatives. The ΔG_v^≠ values obtained by the two different methods agree well with one another. The free enthalpy of activation of the inversion ΔG_v^≠ and of the pseudorotation ΔG_p^≠ both depend on the nature of the substituents. The ΔG_v^≠ values range from 17,9 to 20,5 kcal/mole and the ΔG_p^≠ values are equal to or lower than 11,4 kcal/mole.     

铀(Ⅵ)与不对称希夫碱配合物的合成和热分解反应动力学

邻苯二胺与5－氯－2－羟基二苯酮、邻香草醛作用合成了一种不对称希夫碱配体C₂₇H₂₁N₂O₃Cl（H₂L）。在正丁醇和甲醇体系中硝酸铀酰与该配体反应合成了一种固体希夫碱配合物[UO₂(HL)(NO₃)(H₂O)]·H₂O。通过元素分析、IR、UV、¹H NMR、TG-DTG及摩尔电导率分析等手段对合成的配合物进行了表征,用非等温热重法研究了铀(Ⅵ)配合物的热分解反应动力学,推断出第三步热分解的动力学方程为：d α /d t = A · e^{- E/RT} ·3/2[(1- α )^-1/3-1]^-1,得到了动力学参数E和A。并计算出了活化熵△S^¹和活化吉布斯自由能△G^¹。     

Sels de Pyrylium. XVIII. Etude par RMN du Carbone-13 de Sels d'Aminopyrylium et des Barrières de Rotation dans quelques Cations N,N-Diméthylaminopyrylium

The C-2—N bond of 2-N,N-dimethylaminopyrylium cations has a partial π character due to the conjugation of the nitrogen lone-pair with the ring. The values of ΔG^≠, ΔH^≠, ΔS^≠ parameters related to the corresponding hindered rotation have been determined by ¹³C NMR total bandshape analysis. This conjugation decreases the electrophilic character of carbon C-4 so that the displacement of the alkoxy group is no longer possible. Such a hindered rotation also exists in 4-N,N-dimethylaminopyrylium cations and the corresponding ΔG^≠ parameters have been evaluated. Comparison of these two cationic species shows that hindered rotation around the C—N bond is larger in position 4 than in position 2. Furthermore, the barrier to internal rotation around the C-2? N bond decreases with increasing electron donating power of the substituent at position 4. ΔG^≠ values decreases from 19.1 kcal mol^?1 (79.9 kJ mol^?1) to 12.6 kcal mol^?1 (52.7 kJ mol^?1) according to the following sequence for the R-4 substituents: -C₆H₅, -CH₃, -OCH₃, -N(CH₃)₂.     

Low temperature 13C NMR study of 1-(3-pentyloxyphenylcarbamoyloxy)-2-dialkyl- aminocyclohexanes

Cyclohexane and piperidine ring reversal in 1-(3-pentyloxyphenylcarbamoyloxy)-2-dialkylaminocyclohexanes was investigated by ¹³C NMR. An unusually low conformational energy ΔG = 0.59 kJ mol^?1 and activation parameters ΔG^≠₂₁₈ = 43.8 ± 0.4 kJ mol^?1, ΔH^≠ = 48.9 ± 2.5 kJ mol^?1 and ΔS^≠ = 23 ± 9 J mol^?1 K^?1 were found for the diequatorial to diaxial transition of the cyclohexane ring in the trans-pyrrolidinyl derivative. In the trans-piperidinyl derivative, ΔG₂₂₂ = 44.7 ± 0.5 KJ mol^?1, ΔH^≠ = 55.7 ± 6.3 kJ mol^?1 and ΔS^≠ = 51 ± 21 J mol^?1 K^?1 was found for the piperidine ring reversal from the non-equivalence of the α-carbons.     

NMR and FTIR studies of coordinate-bonding and intramolecular and intermolecular hydrogen bonding in zinc(II)(3,5-diisopropylsalicylate)2

Carboxylate and salicylic OH coordinate bonding as well as intramolecular and intermolecular hydrogen bonding of bis-3,5-diisopropylsalicylatozinc(II), [Zn^II(3,5-DIPS)₂], with Lewis bases were studied to determine mechanisms accounting for antioxidant reactivity of Zn^II(3,5-DIPS)₂. Apparent thermodynamic parameters: K _eq, ΔS ⁰, ΔH ⁰, and ΔG ⁰ were determined for these equilibria with bonding of two molecules of dimethyl sulfoxide-d₆ (DMSO) or ethyl acetate-d₈ (EA) to the Zn^II using NMR and FTIR. We conclude that addition of two equivalents of DMSO or EA to non-polar solutions of Zn^II(3,5-DIPS)₂ results in bonding of DMSO or EA to Zn^II via sulfoxide or ester carbonyl oxygen atoms with ternary complex formation, leading to weakening of carboxylate and salicylic OH coordinate bonding to Zn^II and strengthening intramolecular hydrogen bonding between protons of salicylic OH groups and carboxylate oxygens. Subsequent addition of two or three additional equivalents of DMSO or EA leads to intermolecular hydrogen bonding between protons of salicylic OH groups.     

Quantitative Line-Shape Analysis of Temperature- and Concentration-Dependent 13C-NMR Spectra of 6Li- and 13C-Labelled Organolithium Compounds. Kinetic and Thermodynamic Data for Exchange Processes in Dibromomethyllithium, (Phenylthio)methyllithium,and Butyllithium

Using the ‘permutation of indices’ method proposed by Kaplan and Fraenkel, we could formulate the density-matrix equations required to fit the temperature-dependent ¹³C-NMR spectra observed with the title compounds. For ⁶Li¹³CHBr₂ ( 1 ) and ⁶Li¹³CH₂SC₆H₅ ( 2 ) an exchange mechanism is proposed by which monomers interchange C- and Li-atoms via a non-observed dimeric intermediate; the activation parameters of these intermolecular dynamic processes have been found to be ΔH^≠ = 10.2 kcal/mol, ΔS^≠ = 13.7 cal/mol·K for 1 and ΔH^≠ = 11.1 kcal/mol, ΔS^≠ = 20.6 cal/mol·K for 2 ((D₈)THF as solvent). In the case of (⁶Li)butyllithium ( 3 ), the observed low-temperature spectra indicate that dimeric ( 3b ) and tetrameric ( 3a ) species are in dynamic equilibrium interchanging the C₃HCH₂ groups (and THF molecules) bonded to the ⁶Li-atoms. The relative concentrations of the dimer and of the tetramer have been determined by peak integration or by line-shape fitting; the ‘pseudo’- equilibrium constant, defined by K′_eq = [ 3b ]²/[ 3a ], was found to be 2.6·10^?2 mol/1 (at ?88°) and corresponds to ΔG_R (?88°) = 2 ΔG°_f( 3b ) – ΔG°_f( 3a ) = 1.34 kcal/mol. The activation parameters of the dynamic process responsible for the exchange were estimated as ΔH^≠ = 3.78 kcal/mol and ΔS^≠ = ?31.3 cal/mol·K. Tentative interpretation of the thermodynamic and kinetic parameters is given.     

Thermodynamic activation parameters for viscous flow of aqueous solutions of butylamines

The thermodynamic activation parameters, enthalpies, ΔH?^≠, free energies, ΔG ^≠, and entropies, ΔS?^≠, for viscous flow of the systems, water (W)?+?n-butylamine (NBA), W?+?sec-butylamine (SBA) and W?+?tert-butylamine (TBA), have been determined by using the density and the viscosity data. These properties and their excess values have been represented graphically against their composition. With respect to the composition, ΔG ^≠ show a typical behaviour for all the systems – a fast rise in the water-rich region with a maximum followed by the values that decline up to the pure state of amines. The ΔH?^≠ and ΔS?^≠ versus composition curves follow the similar trend. For all systems the excess properties, ΔG ^≠E, ΔH ^?≠E and ΔS?^≠E are characterized by sharp maxima in the water-rich region, which are thought to be mainly due to the hydrophobic hydration and the hydrophilic effect.     

1H NMR spectra part 31: 1H chemical shifts of amides in DMSO solvent

The ¹H chemical shifts of 48 amides in DMSO solvent are assigned and presented. The solvent shifts Δδ (DMSO‐CDCl₃) are large (1–2 ppm) for the NH protons but smaller and negative (?0.1 to ?0.2 ppm) for close range protons. A selection of the observed solvent shifts is compared with calculated shifts from the present model and from GIAO calculations. Those for the NH protons agree with both calculations, but other solvent shifts such as Δδ(CHO) are not well reproduced by the GIAO calculations. The ¹H chemical shifts of the amides in DMSO were analysed using a functional approach for near ( ≤ 3 bonds removed) protons and the electric field, magnetic anisotropy and steric effect of the amide group for more distant protons. The chemical shifts of the NH protons of acetanilide and benzamide vary linearly with the π density on the αN and βC atoms, respectively. The C=O anisotropy and steric effect are in general little changed from the values in CDCl₃. The effects of substituents F, Cl, Me on the NH proton shifts are reproduced. The electric field coefficient for the protons in DMSO is 90% of that in CDCl₃. There is no steric effect of the C=O oxygen on the NH proton in an NH…O=C hydrogen bond. The observed deshielding is due to the electric field effect. The calculated chemical shifts agree well with the observed shifts (RMS error of 0.106 ppm for the data set of 257 entries). Copyright © 2014 John Wiley & Sons, Ltd.     

How Does the Intrinsic Barrier of Intermolecular Proton Transfer Depend on Molecular Parameters?

The question in the title is of fundamental importance , because the intrinsic barrier ΔG_int^≠ is the key parameter connecting thermodynamics and kinetics. With a valence bond configuration mixing model for proton self-exchange (see picture), it is shown that ΔG_int^≠ is a linear function of I_v−E(σ_NH^*), where I_v is the ionization potential of the base and E(σ_NH^*) the energy of the antibonding orbital of the N−H bond in the conjugated acid. With para-substituted N,N′-dimethylanilines, this manifests itself by a linear relationship between ΔG_int^≠ and the Hammett parameter σ⁺.     

Effects of solvent on the reactions of coordination complexes: Part 17. Kinetics and mechanism of base hydrolysis of (αβS) (salicylato) (tetraethylenepentamine)cobalt (III) in methanol + water and dimethylsulphoxide + water media

The base hydrolysis of (αβS) (salicylato) (tetraethylenepentamine)cobalt(III) has been investigated in MeOH + water and DMSO + water media (0–70% (v/v) cosolvents) at 20.0 ? t°C ? 35.0 and I = 0.10 mol dm^?3 (ClO₄^?). The phenoxide species [(tetren)CoO₂CC₆H₄O]⁺ undergoes both OH^?-independent and OH^?-catalyzed hydrolysis via SN₁ICB and SN₁CB mechanism, respectively. The OH^?-independent hydrolysis of the phenoxide species is catalyzed by both DMSO + water and MeOH + water media, the former exerting a much stronger rate accelerating effect than the latter. The OH^?-catalyzed reaction is strongly accelerated by DMSO + water medium but insensitive to the composition of MeOH + water medium up to 40% (v/v) MeOH beyond which it was not detectable under the experimental conditions. Data analysis has been attempted on the basis of the solvent stabilizing and destabilizing effects on the initial state and transition state of the concerned reactions. The nonlinear variation of the activation parameters, ΔH^≠ and ΔS^≠, with solvent compositions presumably indicates that the solvent structural effects mediate the energetics of solvation of the initial state and transition state of the concerned reactions. The linearity in ΔH^≠ vs. ΔS^≠ plot accomodating all data for k₁ and k₂ paths in DMSO + water and MeOH + water further suggests that the solvent effects on these parameters are mutually compensatory.     

NMR spectroscopic and theoretical study on the isomerism of dimethyl benzodiazepine(diylidene)diacetates

The isomerism of dimethyl 2,2′-(7,8-dichloro-1H-benzo[b][1,4]diazepine-2,4-(3H,5H)diylidene)diacetate ( 1a ) and dimethyl 2,2′-(7,8-dichloro-3-methyl-1H-benzo[b][1,4]diazepine-2,4-(3H,5H)diylidene)diacetate ( 1b ) was investigated by ¹H, ¹³C and ¹⁵N nuclear magnetic resonance (NMR) spectroscopy. In CDCl₃ solution, inversion of the diazepine ring was observed, whereas in (D₆)DMSO and (D₇)DMF solution, besides the ring inversion, a partial cleavage of one chelate ring appeared connected with (E/Z) isomerization about one of the exocyclic C=C bonds. Gibbs free energies (ΔG) and free activation energies (ΔG^≠) were calculated based on B3PW91-SCRF/ZVP DFT computations. Agreement between NMR data and density functional theory (DFT) computations was found.     

Protonenresonanzuntersuchungen an Aminoboranen—II: Einflüsse von para-Phenylsubstituenten auf die Rotationsbarriere um die N?B-Bindung

The electronic influence of substituents on the free enthalpy of rotation around the N? B bond in aminoboranes was investigated in two series of compounds: (a) (CH₃)₂N?BCl (phenyl-p-X), containing the para-phenyl substituent at the boron atom, and (b) (p-X-phenyl)CH₃N?B(CH₃)₂, containing the para-phenyl substituent at the nitrogen atom of the N? B linkage (X = ? NR₂, ? OCH₃, ? C(CH₃)₃, ? Si(CH₃)₃, ? H, ? F, ? Cl, ? Br, ? I, ? CF₃ and ? NO₂). By comparing the rotational barriers in corresponding compounds of both series, a reverse effect of the substituents could be observed. Electron-withdrawing substituents in the para position of the phenyl ring increase the ΔG_c^≠ if the phenyl group is attached to the boron atom; on the other hand, a lower ΔG_c^≠ is observed if the phenyl ring is bonded to the nitrogen atom of the N? B system. Substitution of the phenyl ring with electron-donating substituents in the paraposition exerts the opposite effect. Within each series of compounds, the differences of ΔG_c^≠ values [δ(ΔG_c^≠) = ΔG_c^≠ (X) ? ΔG_c^≠ (X = H)] between substituted and unsubstituted compounds can be explained in terms of inductive and mesomeric effects of the ring substituents and can be correlated with the Hammett σ constant of each substituent. A comparison of the slopes of the plotted lines shows that the influence of the ring substituents is more pronounced in compounds with N-phenyl-p-X than in those with B-phenyl-p-X.