Effect of Different Substituents on Uracil and its 2-Hydroxy-4-oxo Enol Tautomer – A Theoretical Study

2008 ◽  
Vol 63 (10-11) ◽  
pp. 693-702
Author(s):  
Hamzeh S. M. Al-Omari
Keyword(s):  
Free Energy ◽  
Gibbs Free Energy ◽  
Theoretical Study ◽  
Equilibrium Constants ◽  
Semiempirical Method ◽  
Forward Direction ◽  
Heat Of Formation ◽  
Geometrical Parameters ◽  
Homo And Lumo ◽  
Enol Tautomer

The uracil/2-hydroxy-4-oxo uracil tautomeric system was studied by employing the MNDO semiempirical method for the calculations. The uracil structure was found to be energetically favourable as indicated by the calculated heat of formation, the Gibbs free energy, the HOMO and LUMO energies, and charges. The substitution by F, OH, NH2, CH3, and BH2 at the carbon-6 position was found to affect the geometrical parameters of the substituted molecules. All of the substituents were found to shift the equilibrium in forward direction compared to the unsubstituted tautomeric pair as indicated by the calculated values for the equilibrium constants.

Theoretical Study of the Effect of Different α-Substituents on the Acetaldimine-Vinylamine Tautomeric System

2004 ◽  
Vol 59 (6) ◽  
pp. 382-388
Author(s):  
Hamzeh S. M. Al-Omari
Keyword(s):  
Free Energy ◽  
Proton Transfer ◽  
Gibbs Free Energy ◽  
Theoretical Study ◽  
Semiempirical Method ◽  
Heats Of Formation ◽  
Geometrical Parameters

The Acetaldimine-Vinylamine tautomeric system has been studied by employing the MNDO semiempirical method. The imine structure was found to be energetically favorable, as indicated by the calculated heats of formation, Gibbs free energy, LUMO and HOMO, and charges. The substitution of F, Cl, CN, CH3, CF3, NO2 and BH2 at the α-position was found to affect the geometrical parameters. F and Cl substituents are found to favor the imine formation, while CF3, NO2, CN2 and BH2 favor the amine formation. The proton transfer in this tautomeric system is found to be easier (ΔH = 5.224 kcal/mol) than that in the keto-enol tautomeric system (ΔH = 11.1 kcal/mol).

scholarly journals A Theoretical Study of Substituted Cyclobutanones and Their Enols

2004 ◽  
Vol 59 (11) ◽  
pp. 838-844
Author(s):  
Mohammad I. Sway ◽  
Iyad D. Al-Shawabkeh ◽  
Salim M. Khalil
Keyword(s):  
Free Energy ◽  
Gibbs Free Energy ◽  
Theoretical Study ◽  
Theoretical Calculations ◽  
Heats Of Formation ◽  
Geometrical Parameters ◽  
Electron Densities ◽  
Complete Optimization ◽  
Electron Withdrawing Substituents

MINDO-Forces calculations have been performed with complete optimization of the geometry on cyclobutanone and its enol counterpart, perfluorination of cyclobutanones and enol counterparts, and X-cycolobutanones and their X-enols, where X is NO2, CF3, CN, OH, NH2 and F. It was found that ketone is more stable than its enol counterpart. Perfluorination destabilizes ketone on the expense of enol. These results agree with experimental and theoretical calculations. Electron releasing substituents (NH2, OH, F) stabilize cyclobutanone, while electron withdrawing substituents (CF3, NO2) destabilize it. CN substituents have almost no effect on the stabilization of this keto-enol system. Geometrical parameters, heats of formation, electron densities and Gibbs free energy are reported

Semiempirical Method MNDO for the Evaluation of the Effect of Different Substituents at the Imine-Carbon Position on the Acetaldemine-Vinylamine Tauotomerization and Comparison to the Substitution at α-Position

2004 ◽  
Vol 59 (12) ◽  
pp. 987-996
Author(s):  
Hamzeh S. M. Al-Omari
Keyword(s):  
Free Energy ◽  
Charge Distribution ◽  
Energy Gap ◽  
Semiempirical Method ◽  
Free Energy Change ◽  
Isodesmic Reactions ◽  
Mndo Calculations ◽  
Homo And Lumo ◽  
Resonance Stabilization

MNDO calculations have been employed to study the effect of some substituents of the acetaldemine-vinylamine tautomeric system at the imine-carbon position of CH3CXNH, where X = H, F, CN, NH2, NO2, BH2, CH3 and CF3. It is found that the substitutents F, NH2 and NO2 encourage the formation of the enamine tautomer. The substitutents CN, CH3, CF3 and BH2 encourage the formation of the imine tautomer. Isodesmic reactions, free energy change (ΔG), charge distribution and energy gap (Eg) between HOMO and LUMO were used to prove these findings. Resonance stabilization was a major factor in the determination of the most stable tautomer. These results were compared with previous work on the substitution at the σ -carbon position.

Thermodynamics of CuInO2Preparation by Cation Exchange Reaction

2014 ◽  
Vol 33 (4) ◽  
pp. 355-361
Author(s):  
Yun Yao ◽  
Gang Xie ◽  
Ning Song ◽  
Yanqing Hou ◽  
Xiaohua Yu ◽  
...  
Keyword(s):  
Free Energy ◽  
Vapor Pressure ◽  
Cation Exchange ◽  
Exchange Reaction ◽  
Gibbs Free Energy ◽  
Equilibrium Constants ◽  
Thermal Capacity ◽  
Standard Entropy ◽  
Cation Exchange Reaction ◽  
The Way

AbstractTo investigate the optimum conditions of the CuInO2 (CIO) preparation by cation exchange reaction method, the standard entropy, thermal capacity at constant pressure, standard enthalpy and standard Gibbs free energy of formation were estimated. The relations of temperature (T) and thermodynamic equilibrium constants (K), the conditions for three independent reactions were analyzed in CuInO2 preparation. The curves of Gibbs free energy-T, K − T and PCuCl − T for those reactions have been plotted. The results showed that the CIO powder could be synthesized by cation exchange reaction. There were two main reactions through the way of NaInO2 reacting with CuCl. One was NaInO2(s) reacting with CuCl(s) at T ≥ 1698 K. The cost was higher in the way. The other was NaInO2(s) reacting with CuCl(g) at T < 1698 K. However, the yield of CIO would be decreased because CuInO2 powder decomposed into Cu2O(s) and In2O3(s) with the temperature reduced, especially when T ≤ 573 K. And the higher vapor pressure of CuCl(g) was necessary for the process, which needs the higher temperature since the vapor pressure of CuCl(g) increases with increasing temperature, especially when T > 973 K. It was recommended that NaInO2(s) react with CuCl(g) for preparing CIO under conditions of 973 < T ≤ 1698 K and the vacuum in the reactor.

THEORETICAL STUDY OF THE EFFECT OF GEOMETRICAL PARAMETERS AND LOCATION OF ROTOR IMPACT ELEMENTS OF AN IMPACT-CENTRIFUGAL GRINDER ON SPEED AND ANGLES OF CRUSHED PARTICLES FLIGHT

2020 ◽  
Keyword(s):  
Granulometric Composition ◽  
Theoretical Study ◽  
Process Efficiency ◽  
Geometrical Parameters ◽  
Grinding Process ◽  
Main Work ◽  
Impact Element ◽  
The Impact ◽  
Positive Effect ◽  
Efficiency Indicators

One of efficiency indicators of grain grinders is grain granulometric composition. The basis of mixed fodder is crushed grain, the particles of which must have a leveled granulometric composition for subsequent mixing and obtaining a high-quality feed mixture. In agricultural production, hammer crushers are widely used, in which the destruction of grain occurs due to the impact of a hinged hammer. The main disadvantage of these crushers is that not the entire surface of the hammers is involved in grinding, thus reduces grinding process efficiency. A slightly different principle of material destruction is laid down in the basis of the proposed design of the shock-centrifugal grinder. Main work is performed by flat impact elements located on the rotor, which serve to accelerate crushed particles with subsequent impact of them on the bump elements. An important step in the design of new constructions of shock-centrifugal grinders is to determine size and location of the impact elements on the rotor, without which the grinding process is not possible. In the calculation method presented, the dependencies for determining the velocities and angles of a single particle flight from the surface of a flat impact element for its specified dimensions are proposed. Two variants of an impact element location on the rotor are considered and analyzed: radial and at an angle in the direction of rotor rotation. As a result of research carried out, it is noted that in the case of inclined position of an impact element on the rotor an increase in flight speed and flight angles change in crushed particles, which gives the opportunity to have a positive effect on grinding process.

Influence of solvent polarity on the dual fluorescence of p-N,N-dimethylaminobenzonitrile: An AM1 theoretical study

1990 ◽  
Vol 55 (8) ◽  
pp. 1891-1895 ◽  
Author(s):  
Peter Ertl
Keyword(s):  
Excited State ◽  
Theoretical Study ◽  
Solvent Polarity ◽  
Semiempirical Method ◽  
Dual Fluorescence ◽  
Long Wavelength ◽  
Polar Media ◽  
Wavelength Emission ◽  
Ground State Geometry ◽  
Influence Of Solvent

Twisting of the NMe2 group in p-N,N-dimethylaminobenzonitrile (DMABN) was investigated using AM1 semiempirical method with configuration interaction. Effect of polar media was considered by placing + and - charge centers ("sparkles") at appropriate places opposite the molecule. Optimized ground state geometry of DMABN is slightly twisted with the lowest vertical excited state of 1B character. As the polarity of media increases and/or the - NMe2 group twists, the symmetric 1A excited state having considerable charge separation becomes energetically favorable. Anomalous long-wavelength emission of DMABN comes from this state.

Thermodynamics of Flowing Systems: with Internal Microstructure

1994 ◽  
Author(s):  
Antony N. Beris ◽  
Brian J. Edwards
Keyword(s):  
Free Energy ◽  
Theoretical Study ◽  
Flow Behavior ◽  
Irreversible Thermodynamics ◽  
Hamiltonian Mechanics ◽  
Complex Interplay ◽  
Microscopic Models ◽  
Flow Phenomena ◽  
The Subject ◽  
The Continuum

This much-needed monograph presents a systematic, step-by-step approach to the continuum modeling of flow phenomena exhibited within materials endowed with a complex internal microstructure, such as polymers and liquid crystals. By combining the principles of Hamiltonian mechanics with those of irreversible thermodynamics, Antony N. Beris and Brian J. Edwards, renowned authorities on the subject, expertly describe the complex interplay between conservative and dissipative processes. Throughout the book, the authors emphasize the evaluation of the free energy--largely based on ideas from statistical mechanics--and how to fit the values of the phenomenological parameters against those of microscopic models. With Thermodynamics of Flowing Systems in hand, mathematicians, engineers, and physicists involved with the theoretical study of flow behavior in structurally complex media now have a superb, self-contained theoretical framework on which to base their modeling efforts.

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