Relative stability of benziporphyrin and naphthiporphyrin tautomers and the emergence of macrocyclic diatropicity

2014 ◽  
Vol 12 (43) ◽  
pp. 8719-8736 ◽  
Author(s):  
Deyaa I. AbuSalim ◽  
Timothy D. Lash
Keyword(s):  
Relative Stability ◽  
Relative Stabilities ◽  
Good Agreement

The conformations and relative stabilities of a series of benziporphyrin and naphthiporphyrin tautomers were calculated and the diatropic properties of each of these species were assessed. The results were in good agreement with experimental observations and allow favorable delocalization pathways to be identified.

STUDIES ON REACTIONS RELATING TO CARBOHYDRATES AND POLYSACCHARIDES: LXI. PROPERTIES OF THE FRACTIONATED NITRATES OF TWO FRACTIONS OF CORN STARCH

1946 ◽  
Vol 24b (5) ◽  
pp. 246-253 ◽  
Author(s):  
W. R. Ashford ◽  
T. H. Evans ◽  
Harold Hibbert
Keyword(s):  
Relative Stability ◽  
Corn Starch ◽  
Chain Structure ◽  
Linear Type ◽  
Relative Stabilities ◽  
Preferential Adsorption ◽  
Chain Fraction ◽  
Branched Chain ◽  
Nitrogen Contents

Corn starch has been separated into two individual components, arbitrarily designated as amylose (linear fraction) and amylopectin (branched-chain fraction) by means of preferential adsorption on cellulose (Tanret–Pacsu method). These components have been nitrated and their nitrates fractionated by dissolution in ethanol. The relative stabilities and nitrogen contents of the nitrated fractions have been studied.Unfractionated amylose nitrate has greater stability than unfractionated amylopectin nitrate as judged by the Bergmann–Junk test. Dissolution methods of fractionation showed a much higher solubility of the amylopectin nitrate, the greater relative stability of the amylose fractions, and the somewhat greater stabilizing action of ethanol in the case of the latter.The widely different solubilities of amylose and amylopectin nitrates in conjunction with the lower ethanol solubility of whole starch nitrate are in accordance with the theory of a branched-chain structure for amylopectin and the linear type for amylose.

Dodecahedron- and Bowl-Shaped Structures C20

1992 ◽  
Vol 270 ◽  
Author(s):  
Zdenék Slanina ◽  
Ludwik Adamowicz
Keyword(s):  
High Temperature ◽  
Temperature Region ◽  
Relative Stability ◽  
Three Dimensional ◽  
Two Dimensional ◽  
High Temperature Region ◽  
Relative Stabilities ◽  
One Dimensional ◽  
Very High ◽  
Quantumchemical Method

ABSTRACTPurely carbonaceous aggregates C20 have been studied by the AM1 quantumchemical method. In addition to one dodecahedron-shaped structure possessing C1 symmetry another three-dimensional species is revealed, viz. a bowl-shaped structureof C5v symmetry (and also one two-dimensional and two one-dimensional species). Temperature dependence of the relative stabilities of both three-dimensional structures is evaluated, showing that in the relevant temperature region the fullerenic species is prevailing. However, in a very high temperature region a relative-stability interchange has been predicted.

Energetics of Intra- and Inter-molecular Bonds in the Three Nitrophenols

1994 ◽  
Vol 47 (9) ◽  
pp. 1651 ◽  
Author(s):  
R Sabbah ◽  
M Gouali
Keyword(s):  
Thermal Analysis ◽  
Hydrogen Bond ◽  
Heat Capacity ◽  
Differential Thermal Analysis ◽  
Relative Stability ◽  
Intermolecular Bond ◽  
Resonance Energies ◽  
Heat Capacity Measurements ◽  
Intramolecular Hydrogen ◽  
Good Agreement

A thermodynamic study of the three nitrophenol isomers (general formula C6H5NO3) was realized by combustion calorimetry of small amounts of substance (a few milligrams), sublimation calorimetry, differential thermal analysis and heat capacity measurements. The experimental enthalpies of combustion, sublimation and fusion of these compounds are as follows: ortho para -ΔcH�m(s,298.15K)/kJ mol-1 2871.0�1.3 2875.1�0.9 2868.5�1.0 ΔsubH�m(298.15K)/kJ mol-1 72.30�0.28 91.23�0.49 92.39�0.43 ΔfusHm/kJ mol-1 18.32�0.35 20.54�0.34 17.33�0.10 Ttriple point/K 318.40�0.01 370.51�0.01 387.26�0.05   The strength of the intramolecular hydrogen bond in the ortho isomer was estimated equal to 20.09 kJ mol-1. The relative stability of the three isomers is discussed, and the intermolecular bond enthalpies have been determined. The experimental resonance energies Eexp,conj are 168.7, 142.8 and 148.2 kJ mol-1 for ortho -, meta- and para-nitrophenol respectively, and are in good agreement with theoretical values. The experimental atomization enthalpies Δa,expH°m(298.15K) are 6742.5�1.9, 6719.5�1.7 and 6724.9�1.8 kJ mol-1 for ortho -, meta- and para-nitrophenol respectively.

Ab Initio Theoretical Studies of Relative Stabilities and IR Spectrum of 5-Methylcytosine Tautomers

2003 ◽  
Vol 2003 (4) ◽  
pp. 195-199 ◽  
Author(s):  
Lida Ghassemzadeh ◽  
Majid Monajjemi ◽  
Karim Zare
Keyword(s):  
Density Functional Theory ◽  
Gas Phase ◽  
Density Functional ◽  
Relative Energy ◽  
Theoretical Studies ◽  
Functional Theory ◽  
Relative Stabilities ◽  
B3lyp Method ◽  
Wide Range ◽  
Good Agreement

The structure and relative energies of the tautomers of 5-methylcytosine in the gasphase and in different solvents are predicted using MP2 and density functional theory methods. The order of stability for these tautomers is C3>C1>C2>C4>C5>C6 calculated by MP2 and C1>C3>C2>C4>C5>C6 calculated by the B3LYP method. Relative energy calculations are performed in wide range of solvent dielectrics and in all solvents the oxo-amino C1 is predicted as the most stable tautomer. The infrared spectra of two dominant tautomers are calculated in the gas phase using HF and density functional theory. Good agreement between calculated (DFT) and experimental harmonic vibrational frequencies is found.

MINDO-Forces Study on the Relative Stabilities of Hydroxy- and Aminopyridine Tautomers

1985 ◽  
Vol 40 (12) ◽  
pp. 1278-1282 ◽  
Author(s):  
Salim M. Khalil
Keyword(s):  
Relative Stabilities ◽  
Experimental Values ◽  
Good Agreement

Relative stabilities of monosubstituted hydroxy- and aminopyridine tautomers have been calculated using the semiempirical MINDO-Forces MO method with full geometries optimization. The lactim tautomers proved to be more stable except in the case of 2-hydroxypyridine. The results are in good agreement with some theoretical and experimental values.

Isomeric Higher and Smaller Fullerenes: A Profound Enthalpy/Entropy Interplay

1999 ◽  
Vol 593 ◽  
Author(s):  
X. Zhao ◽  
Z. Slanina ◽  
E. Ōsawa
Keyword(s):  
Harmonic Oscillator ◽  
Ab Initio ◽  
Quantum Chemical ◽  
Temperature Effects ◽  
Rigid Rotator ◽  
Relative Stabilities ◽  
Rotator Model ◽  
Complete Set ◽  
Good Agreement

ABSTRACTComputations of isomeric fullerenes are performed at semiempirical and ab initio quantum-chemical levels: C36, C72, C88. C36 fullerenes and quasi-fullerenes are computed at the SAM1 level, and then at the B3LYP/6-31G* level. Altogether 598 cages are considered. The SAM1 method is also applied to C72, i.e., the solitary isolated-pentagon-rule (IPR) structure and several non-IPR isomers. Finally, the complete set of thirty five topologically different IPR isomers of C88 is computed. In all the cases, energetics is combined with entropy contributions based on the harmonic-oscillator and rigid-rotator model. Considerable temperature effects on the relative stabilities in the systems are found. Relationships to available observed data are discussed throughout and a good agreement is found.

Modélisation classique de champs de forces d’interactions additives dans les agrégats de type X+ Arn, (X = Li et K); mécanisme de croissance

2008 ◽  
Vol 86 (7) ◽  
pp. 911-918 ◽  
Author(s):  
F Ben Salem ◽  
F Taarit ◽  
M Ben El Hadj Rhouma ◽  
Z Ben Lakhdar
Keyword(s):  
Monte Carlo ◽  
Mass Spectrum ◽  
Potential Energy ◽  
Relative Stability ◽  
Potential Energy Surfaces ◽  
Point Of View ◽  
Magic Numbers ◽  
Energy Surfaces ◽  
Structural Point ◽  
Good Agreement

The structure and stability of the Li+Arn and K+Arn clusters are studied using pair additive potentials adapted to reproduce the ab initio calculations that we estimate as the most accurate for the Li+Ar, K+Ar, and Ar–Ar dimers. The exploration of the potential energy surfaces of the Li+Arn and K+Arn systems was carried out with Wales’ method, which includes Monte-Carlo and deformation methods. From a structural point of view, one identifies a construction mechanism in very good agreement with the interpretation of the mass spectrum done by Velegrakis, including a difference for the n = 10 case. The study of the relative stability of these structures yields magic numbers for n = 8, 10, 14, 16, 18, 20, 22, 30, 32, and 34, which are in good agreement with the experiment. [Journal translation]

Molecular conformations of ortho-substituted benzophenones

1976 ◽  
Vol 54 (2) ◽  
pp. 226-230 ◽  
Author(s):  
Felice Zuccarello ◽  
Salvatore Millefiori ◽  
Salvatore Trovato
Keyword(s):  
Electrostatic Interactions ◽  
Minimum Energy ◽  
Molecular Conformations ◽  
Relative Stabilities ◽  
Contour Maps ◽  
Semiempirical Approach ◽  
Relevant Role ◽  
Geometrical Data ◽  
Highly Strained ◽  
Good Agreement

The minimum energy conformations of some mono- and di-substituted benzophenones were determined from contour maps of potential energy calculated by a semiempirical approach. The electrostatic interactions play a relevant role in the relative stabilities when different minima are possible. Comparison with the available experimental data reveals a good agreement with geometrical data, and a poorer agreement with energies in highly strained conformations.

Relative stabilities of M/NHC complexes (M = Ni, Pd, Pt) against R–NHC, X–NHC and X–X couplings in M(0)/M(ii) and M(ii)/M(iv) catalytic cycles: a theoretical study

2019 ◽  
Vol 48 (45) ◽  
pp. 17052-17062 ◽  
Author(s):  
Alexander V. Astakhov ◽  
Safarmurod B. Soliev ◽  
Evgeniy G. Gordeev ◽  
Victor M. Chernyshev ◽  
Valentine P. Ananikov
Keyword(s):  
Dft Calculations ◽  
Relative Stability ◽  
Theoretical Study ◽  
Reductive Elimination ◽  
Catalyst Stability ◽  
Relative Stabilities ◽  
Elimination Reactions ◽  
Catalytic Cycles

DFT calculations reveal relative stability of MII/NHC and MIV/NHC complexes of nickel, palladium and platinum against the R–NHC coupling and various reductive elimination reactions that influence catalyst stability/decomposition.

Structure, vibrations and relative stability of 1-methylcyclobutene and methylenecyclobutane tautomers using DFT and CCSD methods

2017 ◽  
Vol 16 (05) ◽  
pp. 1750041 ◽  
Author(s):  
Mohammed I. Alomari ◽  
Taher S. Ababneh ◽  
Tareq M. A. Alshboul
Keyword(s):  
Experimental Data ◽  
Spectroscopic Analysis ◽  
Geometrical Parameters ◽  
Stable Isomer ◽  
Relative Stabilities ◽  
Infrared Spectroscopic Analysis ◽  
Energy Formula ◽  
High Level ◽  
Ab Initio And Dft ◽  
Good Agreement

In this study, geometrical optimizations, infrared spectroscopic analysis and relative stabilities of 1-methylcyclobutene and methylenecyclobutane tautomers were investigated by utilizing high-level ab initio and DFT calculations. The thermodynamic data showed that 1-methylcyclobutene is the more stable isomer with enthalpy [Formula: see text][Formula: see text]kcal/mol and Gibbs energy [Formula: see text][Formula: see text]kcal/mol lower than that for methylenecyclobutane at the M06/aug-cc-PVTZ level of theory. These results are in good agreement with the available experimental data. Additionally, the geometrical parameters and vibrational frequencies agree well with the recorded results in literatures.

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