Validation of Enthalpy–Entropy Compensation Mechanism in Partial Amide Bond Rotation

Guerra, Jacob; Bajwa, Bhvandip S.; Kumar, Prarthana; Vazquez, Salvador; Krishnan, Viswanathan V; Maitra, Soumyajit

doi:10.1021/acsomega.0c00332

Cited by 8 publications

(8 citation statements)

References 35 publications

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“…Similar behavior of enthalpyentropy compensation (EEC) behavior has been published elsewhere in various fields [42][43][44][45]. The narrow range of Gibbs free energy (ΔG) and the interdependence of enthalpy (ΔH) and entropy (ΔS) in the same system strongly indicate the effect of a kinetic compensation effect [46]. Eby assumed that different relaxation phenomena in the polymers were attributed to self-diffusion of chains and stated that the above relation should be appropriate for the activation criteria defined in the relaxation studies [47].…”

Section: Substitution Of Equation (3) Into Equation (2)supporting

confidence: 68%

TSDC of Irradiated and Non-Irradiated Cellulose Acetate

et al. 2021

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Films of cellulose acetate (CA) have been prepared by casting method using tetrahydrofuran (THF). CA films are γ-irradiated with varying radiation doses of 10, 20, 30, 40, 50 and 60 kGy using cobalt-60 ( 60 Co) source. Global thermally stimulated depolarization current (TSDC) of non-irradiated and irradiated CA samples has been investigated under the effect of various poling electric field (Ep) in a temperature range from 300 K to 440 K. It is observed that, global TSDC spectra of non-irradiated and irradiated CA samples are characterized by two relaxation peaks. One in the low temperature range ~321 K and the other in the high temperature range ~ 376-383 K are observed for non-irradiated sample. On the other hand, these temperatures are shifted towards lower temperature for irradiated samples to be located at 317 K and ~371 K. These relaxations are assigned as  and -relaxation and attributed to molecular motion of the polar acetate groups, C2H3O2 and polarization of the space charges, respectively. TStechnique has been carried out to decompose global TSDC spectra of all samples into its elementary peaks and the molecular parameters such as, activation energy and pre-exponential factor are calculated for each TS peak. Relaxation map (RM) of all samples has been analyzed using Eyring transformation and thermodynamic parameters such as, enthalpy activation (H), entropy activation (S) and Gibbs free energy (G) are estimated. The compensation phenomenon was verified by the linear relationship between both enthalpy and entropy.

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Section: Substitution Of Equation (3) Into Equation (2)supporting

confidence: 68%

TSDC of Irradiated and Non-Irradiated Cellulose Acetate

et al. 2021

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“…In a recent article Guerra et al [36] investigate Enthalpy‐Entropy Compensation in Partial Amide Bond Rotation using N,N‐Diethyl‐m‐toluamide (DEET) as a model system to exploit chemical exchange caused by restricted rotation about the amide bond. As application of our method we consider the 12 molecules with an amine substitution by pyrrolidine and also by piperidine.…”

Section: Application To Some Examplesmentioning

confidence: 99%

Simple Accurate Verification of Enthalpy‐Entropy Compensation and Isoequilibrium Relationship

Griessen

Dam

2021

ChemPhysChem

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In many experimental investigations of thermodynamic equilibrium or kinetic properties of series of similar reactions it is found that the enthalpies and entropies derived from Van ′t Hoff or Arrhenius plots exhibit a strong linear correlation. The origin of this Enthalpy‐Entropy compensation, which is strongly related to the coalescence tendency of Van ′t Hoff or Arrhenius plots, is not necessarily due to a physical/chemical/biological process. It can also be a merely statistical artefact. A new method, called Combined K‐CQF makes it possible both to quantify the degree of coalescence of experimental Van ‘t Hoff lines and to verify whether or not the Enthalpy‐Entropy Compensation is of a statistical origin at a desired confidence level. The method is universal and can handle data sets with any degree of coalescence of Van ‘t Hoff (or Arrhenius) plots. The new method requires only a standard least square fit of the enthalpyΔH versus entropy ΔS plot to determine the two essential dimensionless parameters K and CQF. The parameter K indicates the position (in inverse temperature) of the coalescence region of Van ‘t Hoff plots and CQF is a quantitative measure of the smallest spread of the Van ‘t Hoff plots. The position of the (K, CQF) couple with respect to universal confidence contours determined from a large number of simulations of random Van ‘t Hoff plots indicates straightforwardly whether or not the ΔH‐ΔS compensation is a statistical artefact.

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“…The spectral characterization is consistent with the previous studies on this molecule (Figure S1). 32,33 Figure 2a shows the first NMR spectrum in the spectrometer ($10 min), representing the system close to a crossover or coalescence limit, k ex $ jν A À ν B j = Δν under a two-site exchange situation. As evidenced by the traces in the stacked plot (Figure 2a), the chemical shift difference between the methylene protons increases, and spectral features sharpen with time.…”

Section: Resultsmentioning

confidence: 99%

“…23,24,27,31 Molecule (1) (1-(3-methylbenzoyl) pyrrolidine) (Figure 2 insert) is another molecule that is shown to have similar double-bond characteristics. 32 The line shape changes due to the chemical exchange process in this model system (1) in chloroform is employed to investigate the combined effect of thermal convection and liquid-vapor thermal equilibrium process. Experiments were performed at multiple experimental conditions, including variation in sample temperatures in both sealed and unsealed samples.…”

Section: Introductionmentioning

confidence: 99%

To flame‐seal or not to flame‐seal NMR tubes: The role of liquid–vapor equilibria on the accuracy of variable temperature experiments

Morrelli,

Maitra,

Krishnan

2023

Magnetic Reson in Chemistry

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In NMR experiments, it is crucial to control the temperature of the sample, especially when measuring kinetic parameters. Usually, it takes 2 to 5 min for the temperature of the sample inside the NMR probe to stabilize at a fixed value set for the experiment. However, the NMR sample tubes are flame‐sealed in some cases, such as when working with volatile solvents, atmosphere‐sensitive samples, or calibration samples for long‐term use. When these samples are placed inside the NMR probe, the spectrometer controls the lower portion (liquid phase) of the NMR sample tube with a gas flow at a fixed temperature, while the upper portion (vapor) is at ambient temperature. This probe design creates a unique temperature gradient across the sample, leading to vapor pressure build‐up, particularly inside a sealed NMR tube. By analyzing the temperature‐dependent spectral line shape changes of a chemical exchange process, we report that under standard experimental conditions, the sample temperature can take up to 2 to 3 h (instead of minutes) to stabilize. The time scale of the liquid–vapor equilibrium process is much slower, with a half‐life exceeding 35 min, in contrast to the 2‐min duration required to obtain each spectrum. This phenomenon is exclusively due to the liquid–vapor equilibrium process of the flame‐sealed NMR tube and is not observable otherwise.

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Validation of Enthalpy–Entropy Compensation Mechanism in Partial Amide Bond Rotation

Cited by 8 publications

References 35 publications

TSDC of Irradiated and Non-Irradiated Cellulose Acetate

TSDC of Irradiated and Non-Irradiated Cellulose Acetate

Simple Accurate Verification of Enthalpy‐Entropy Compensation and Isoequilibrium Relationship

To flame‐seal or not to flame‐seal NMR tubes: The role of liquid–vapor equilibria on the accuracy of variable temperature experiments

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