Effects of Substituents on the Barriers to Rotation in Phenyl and Benzyl Carbamates

1986 ◽  
Vol 39 (3) ◽  
pp. 457 ◽  
Author(s):  
C Yamagami ◽  
N Takao ◽  
Y Takeuchi
Keyword(s):  
Free Energy ◽  
Steric Effect ◽  
Inductive Effect ◽  
Resonance Effect ◽  
Substituent Effects ◽  
Energy Of Activation ◽  
Resonance Effects ◽  
Free Energy Of Activation

The free energy of activation for rotation about the C-N bond (ΔG‡Tc) in substituted phenyl and benzyl N,N- dimethylcarbamates was determined by the 13C dynamic n.m.r. method. The ΔG‡Tc value depended linearly on Hammett's σ with positive p. We have separated the substituent effects into inductive and resonance effects by using dual substituent parameter ( d.s.p .) analysis, and found that the resonance effect is more important than the inductive effect for para derivatives, and vice versa for meta derivatives. General trends of electronic substituent effects on barriers to rotation in carbamates and structurally related amides are also discussed. The ortho steric effect was small.

Viscosity of Dimethyl Sulfoxide + 1,4 Dimethylbenzene System

2008 ◽  
Vol 59 (1) ◽  
pp. 45-48
Author(s):  
Oana Ciocirlan ◽  
Olga Iulian
Keyword(s):  
Free Energy ◽  
Dimethyl Sulfoxide ◽  
Atmospheric Pressure ◽  
Entire Range ◽  
Polynomial Equation ◽  
Energy Of Activation ◽  
Excess Gibbs Free Energy ◽  
Experimental Measurements ◽  
Gibbs Energy Of Activation ◽  
Free Energy Of Activation

This paper reports the viscosities measurements for the binary system dimethyl sulfoxide + 1,4-dimethylbenzene over the entire range of mole fraction at 298.15, 303.15, 313.15 and 323.15 K and atmospheric pressure. The experimental viscosities were correlated with the equations of Grunberg-Nissan, Katti-Chaudhri, Hind, Soliman and McAllister; the adjustable binary parameters have been obtained. The excess Gibbs energy of activation of viscous flow (G*E) has been calculated from the experimental measurements and the results were fitted to Redlich-Kister polynomial equation. The obtained negative excess Gibbs free energy of activation and negative Grunberg-Nissan interaction parameter are discussed in structural and interactional terms.

The crystal structure of ethyl-Z-3-amino-2-benzoyl-2-butenoate and measurement of the barrier to E,Z-isomerization

1980 ◽  
Vol 58 (17) ◽  
pp. 1821-1828 ◽  
Author(s):  
Gary D. Fallon ◽  
Bryan M. Gatehouse ◽  
Allan Pring ◽  
Ian D. Rae ◽  
Josephine A. Weigold
Keyword(s):  
Crystal Structure ◽  
Nuclear Magnetic Resonance ◽  
Hydrogen Bond ◽  
Free Energy ◽  
Magnetic Resonance ◽  
Energy Of Activation ◽  
X Ray ◽  
X Ray Crystallography ◽  
Free Energy Of Activation ◽  
Nuclear Magnetic

Ethyl-3-amino-2-benzoyl-2-butenoate crystallizes from pentane as either the E (mp 82–84 °C) or the Z-isomer (mp 95.5–96.5 °C). The E isomer is less stable, and changes spontaneously into the Z, which bas been identified by X-ray crystallography. The structure is characterised by an N–H/ester CO hydrogen bond and a very long C2—C3 bond (1.39 Å). Nuclear magnetic resonance methods have been used to measure the rate of [Formula: see text] isomerization at several temperatures, leading to the estimate that the free energy of activation at 268 K is 56 ± 8 kJ.

Article

1999 ◽  
Vol 77 (5-6) ◽  
pp. 934-942
Author(s):  
J Peter Guthrie
Keyword(s):  
Carbon Dioxide ◽  
Free Energy ◽  
Equilibrium Constants ◽  
Marcus Theory ◽  
Energy Of Activation ◽  
Free Energies ◽  
Orbital Theory ◽  
Activation Free Energy ◽  
Free Energy Of Activation ◽  
Rms Error

Rate constants for hydration of carbon dioxide and ketene can be calculated by applying No Barrier Theory, which needs only equilibrium constants and distortion energies, the latter calculated using molecular orbital theory. The calculated free energies of activation are in satisfactory agreement with experiment: the rms error in free energy of activation is 2.38 kcal/mol. These compounds can also be described using Marcus Theory or Multidimensional Marcus Theory using the transferable intrinsic barrier appropriate to simple carbonyl compounds; in this case the rms error in free energy of activation is 2.19 kcal/mol. The two methods agree on preferred mechanistic path except for uncatalyzed hydration of ketene where Multidimensional Marcus Theory leads to a lower activation free energy for addition to the C=O, while No Barrier Theory leads to a lower free energy of activation for addition to the C=CH2. A rate constant for hydroxide ion catalyzed hydration of ketene can be calculated and is in accord with preliminary experimental results.Key words: ketene, carbon dioxide, hydration, Marcus Theory, No Barrier Theory.

SOME THEORETICAL ASPECTS OF ELECTRON-TRANSFER PROCESSES IN AQUEOUS SOLUTION

1959 ◽  
Vol 37 (1) ◽  
pp. 138-147 ◽  
Author(s):  
Keith J. Laidler
Keyword(s):  
Aqueous Solution ◽  
Electron Transfer ◽  
Free Energy ◽  
Energy Of Activation ◽  
Theoretical Treatment ◽  
Free Energy Of Activation ◽  
Diffusion Controlled ◽  
Entropy Of Activation ◽  
Pass Through ◽  
Electron Transfer Processes

A theoretical treatment has been developed for the rates of electron-transfer reactions in aqueous solution, with particular reference to the ferric–ferrous system. The reactions are considered to be diffusion-controlled processes, the approach of the ions being hindered by the electrostatic repulsion between them. Calculations have been made of the free energy of the diffusion process and for the repulsion, account being taken of the variation in dielectric constant with the electric field. The form of the potential-energy barrier between the ions is calculated for various separations, and the transmission coefficient calculated using the quantum-mechanical expression corresponding to a rectangular barrier. The total free energy of activation for the reaction, which is the sum of the contributions due to diffusion, repulsion, and tunnelling, is found to pass through a minimum at a separation of about 4 Å. The calculated free energy of activation for the reaction is 15.4 kcal, in good agreement with the experimental value of 16.8 kcal. The energy and entropy of activation for the reaction are also briefly discussed.

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