Electronic effects on enol acidity and keto-enol equilibrium constants for ring-substituted 2-tetralones

1999 ◽  
Vol 77 (5-6) ◽  
pp. 634-638 ◽  
Author(s):  
Xudong Yao ◽  
Ralph M Pollack
Keyword(s):  
Aqueous Solution ◽  
Charge Transfer ◽  
Systematic Study ◽  
Free Electron ◽  
Electron Pair ◽  
Equilibrium Constants ◽  
Hydroxyl Group ◽  
Negative Deviation ◽  
Electronic Effects ◽  
Free Electron Pair

Equilibrium constants for the ionization of a variety of phenyl-substituted 2-tetralones (pKaK), for the ionization of their enols (pKaE), and for keto-enol tautomerization (pKE) were determined. Hammett plots of pKaK and pKaE vs. σ- are linear with slopes (-ρ) of -1.66 ± 0.06 and -0.90 ± 0.03, respectively, except for deviations of the points corresponding to 6-nitro-2-tetralone (1b) and its enol. We have previously attributed the negative deviation of 1b from the correlation for the acidities of the ketones obtained with the more limited set of data to the lack of a free electron pair on C-1 of the free tetralone (Nevy et al.). The negative deviation of the point for 1b from the correlation for the acidities of the enols suggests that charge transfer from the hydroxyl group of the enol to the nitro group is less important than it is for phenols. This study represents the first systematic study of electronic effects on equilibria among ketone, enol, and enolate in aqueous solution. Key words: enol, acidity, equilibrium, substituent, conjugation.

scholarly journals Structure and hydrogen bonding of the hydrated selenite and selenate ions in aqueous solution

2014 ◽  
Vol 43 (17) ◽  
pp. 6315-6321 ◽  
Author(s):  
Lars Eklund ◽  
Ingmar Persson
Keyword(s):  
Aqueous Solution ◽  
Hydrogen Bonding ◽  
Free Electron ◽  
Electron Pair ◽  
Bound Water ◽  
Water Molecules ◽  
Hydration Sphere ◽  
Free Electron Pair

The selenite ion has an asymmetric hydration sphere with loosely electrostatically bound water molecules outside the free electron pair.

Organic Sulfur Mechanisms. 17. A Brief Study of the Photolysis of an Unsaturated Cyclic Sulfone

1975 ◽  
Vol 53 (23) ◽  
pp. 3656-3659 ◽  
Author(s):  
J. F. King ◽  
E. G. Lewars ◽  
D. R. K. Harding ◽  
R. M. Enanoza
Keyword(s):  
Free Electron ◽  
Ring Opening ◽  
Electron Pair ◽  
Heterocyclic Ring ◽  
Organic Sulfur ◽  
Free Electron Pair

Photolysis of 3-phenyl-2H-thiopyran 1,1-dioxide (3) in methanol gives a mixture of 3-phenyl-5-methoxy-5,6-dihydro-2H-thiopyran 1,1-dioxide (4) and methyl 4-phenyl-2,4-pentadiene-1-sulfonate (5). Formation of 5 shows that the photochemical ring opening of cyclohexadienic sulfonyl compounds (1) does not require an atom bearing a free electron pair in the heterocyclic ring, and therefore argues in favor of a mechanism involving cycloreversion to the sulfene (1 → 2).

Darstellung und Kristallstruktur von K2Sb4S7 · H2O / Preparation and Crystal Structure of K2Sb4S7 · H2O

1979 ◽  
Vol 34 (3) ◽  
pp. 383-385 ◽  
Author(s):  
Brigitte Eisenmann ◽  
Herbert Schäfer
Keyword(s):  
Crystal Structure ◽  
Free Electron ◽  
Electron Pair ◽  
Three Dimensional ◽  
The Other ◽  
Water Molecules ◽  
Triclinic System ◽  
Dimensional Network ◽  
Free Electron Pair

Abstract K2Sb4S7 · H2O crystallizes in the triclinic system with a = 1171.4(5) pm, b = 952.0(5) pm, c = 715.6(5) pm and α = 99.36(5)°, β = 86.80(5)°, γ= 103.48(5)°. One half of the Sb atoms has three sulfur neighbours forming with the free electron pair a ψ-ShS3 tetrahedron, while the other half is coordinated by four S atoms to build a ψ-trigonal SbS4 bipyramid. These polyhedra are connected by common edges and corners to a three-dimensional network with two types of channels, in which either K+ ions only or K+ ions and water molecules are located.

scholarly journals Carbonyl Addition Reactions: Factors Affecting the Hydrate–Hemiacetal and Hemiacetal–Acetal Equilibrium Constants

1975 ◽  
Vol 53 (6) ◽  
pp. 898-906 ◽  
Author(s):  
J. Peter Guthrie
Keyword(s):  
Aqueous Solution ◽  
Carbonyl Compounds ◽  
Equilibrium Constants ◽  
Substituent Effects ◽  
Steric Effects ◽  
Addition Reactions ◽  
Free Energies ◽  
Electronic Effects ◽  
Factors Affecting ◽  
Analogous Formula

Equilibrium constants for hydrate–hemiacetal interconversion in aqueous solution at 25° have been measured for four fluorinated carbonyl compounds: compound, alcohol, K4 (M−1): CF3CHO, C2H5OH, 2.3; CF3COCH3, CH3OH, 1.0; CF3COPh, CH3OH, 3.5; CF3COCF3, CH3OH, 0.14. These values, combined with values from the literature, permit an examination of substituent effects upon the equilibrium constant for[Formula: see text]The free energy change for this process, corrected for symmetry and steric effects, follows the equation[Formula: see text]Thus electronic effects upon this equilibrium are generally small and in fact are often smaller than steric effects.This analysis permits and justifies the calculation of free energies of formation of [Formula: see text] compounds from the (more generally measurable) free energies of formation of the analogous [Formula: see text] compounds.

Influence of protonation of peripheral substituents on photophysical and photochemical properties of tetrapyrazinoporphyrazines

2010 ◽  
Vol 14 (07) ◽  
pp. 582-591 ◽  
Author(s):  
Veronika Novakova ◽  
Eva H. Mørkved ◽  
Miroslav Miletin ◽  
Petr Zimcik
Keyword(s):  
Charge Transfer ◽  
Sulfuric Acid ◽  
Singlet Oxygen ◽  
Electron Pair ◽  
Intramolecular Charge Transfer ◽  
Quantum Yields ◽  
Considerable Decrease ◽  
Fluorescence Quantum Yields ◽  
Photochemical Properties ◽  
Free Electron Pair

Octasubstituted zinc tetrapyrazinoporphyrazines with four N,N-dimethylaminophenyls and four phenyl or pyridin-3-yl substituents were synthesized and fully characterized. Their fluorescence quantum yields in DMF or pyridine were very low, almost undetectable, as a consequence of ultrafast intramolecular charge transfer. Titration of their DMF solutions with sulfuric acid led to increase of the fluorescence quantum yields by two orders of magnitude when the full protonation of peripheral substituents was achieved. Intramolecular charge transfer is no longer a favorable way of excited-state relaxation at full protonation of N,N-dimethylaminophenyl substituents because of loss of donor centers (free electron pair on its nitrogen). Similarly, singlet oxygen quantum yields also increased by two orders of magnitude when sulfuric acid was added to tetrapyrazinoporphyrazine solutions in DMF. Protonation at azomethine nitrogens of tetrapyrazinoporphyrazine macrocycle was observed at higher acid concentrations and it led to considerable decrease of fluorescence quantum yields. Octaphenyl zinc tetrapyrazinoporphyrazine and octa(pyridin-3-yl) zinc tetrapyrazinoporphyrazine were used as controls without intramolecular charge transfer. Their fluorescence and singlet oxygen quantum yields were high in DMF and decreased at higher concentrations of sulfuric acid due to protonation of azomethine nitrogens. The results suggest that the photophysical and photochemical properties of studied compounds may be controlled by changes of pH of medium.

Zum Bindungszustand des fünf- und sechsbindigen Siliciums in kationischen und anionischen o-Arylendioxychelaten / (d ← n) π-Bonding in Anionic and Cationic o-Arylenedioxy Chelates of Hexacoordinate and Pentacoordinate Silicon Studied by Means of ESCA

1974 ◽  
Vol 29 (1-2) ◽  
pp. 72-74 ◽  
Author(s):  
Heinrich Meyer ◽  
Günter Nagorsen
Keyword(s):  
Linear Correlation ◽  
Free Electron ◽  
Linear Relation ◽  
Good Yield ◽  
Electron Pair ◽  
Binding Energies ◽  
Considerable Extent ◽  
Silicon Compounds ◽  
Back Donation ◽  
Free Electron Pair

The “Si-2s- and Si-2p-binding energies” of 5 o-arylenedioxy complexes containing penta- and hexacoordinate silicon have been obtained from their ESCA-spectra. The data have been compared to those of tetracovalent silicon compounds. A linear correlation between calculated Pauling charges and binding energies has been found for compounds where no (d ← n) -interaction should exist. Characteristic deviations from the linear relation were found both in tetravalent silicon compounds containing Si-O-bonds, the (d ← n)π-interaction of which is well established, and in the anionic tris(o-phenylenedioxy) siliconate and in the bis(o-phenylenedioxy) organosiliconates. No deviations were observed in case of the cationic 6-coordinate complexes of silicon with acetylacetone and 2-hydroxypyridine-N-oxide. We conclude that an additional back donation from the free electron pair (dSi ← nOo) only exists to a considerable extent in tetracovalent silicic ester derivatives, in the hexa- and pentacoordinate tris(o-phenylendioxy) siliconate and in the bis(o-phenylenedioxy) organosiliconates. A method is given to obtain crystalline tris(2-oxypyridine-N-oxy) siliconium chloride in good yield.

Difficulties in the interaction of the free electron pair in diacetophosphides and diacetamides

1968 ◽  
Vol 17 (2) ◽  
pp. 377-380
Author(s):  
R. G. Kostyanovskii ◽  
V. V. Yakshin ◽  
S. L. Zimont ◽  
I. I. Chervin
Keyword(s):  
Free Electron ◽  
Electron Pair ◽  
Free Electron Pair

Kinetics and mechanism of gold(III) incorporation into tetrakis(1-methylpyridium-4-yl)porphyrin in aqueous solution

2004 ◽  
Vol 08 (11) ◽  
pp. 1269-1275 ◽  
Author(s):  
Ahsan Habib ◽  
Masaaki Tabata ◽  
Ying Guang Wu
Keyword(s):  
Aqueous Solution ◽  
Rate Constants ◽  
Kinetic Data ◽  
Ph Dependence ◽  
Equilibrium Constants ◽  
Hydroxyl Group ◽  
Net Charge ◽  
First Order ◽  
Kinetics Of ◽  
Hydrolysis Of

The kinetics of the reaction of the tetrakis(1-methylpyridium-4-yl)porphyrin tetracation, [ H 2( TMPyP )]4+, with gold(III) ions were studied along with equilibria of gold(III) species in aqueous medium at 25°C, I = 0.10 M ( NaNO 3). The equilibrium constants for the formation of [ AuCl 4-n( OH ) n ]- ( n = 0,…,4), defined as β n = [ AuCl 4- n ( OH ) n ]- [ Cl -] n / [ AuCl 4-][ OH -] n were found to be that log β1 = 7.94 ± 0.03, log β2 = 15.14 ± 0.03, log β3 = 21.30 ± 0.05 and log β4 = 26.88 ± 0.05. The overall reaction was first order with respect to each of the total [ Au (III)] and [ H 2 TMPyP 4+]. On the basis of pH dependence on rate constants and the hydrolysis of gold(III), the rate expression can be written as d [ Au ( TMPyP )5+]/ dt = ( k 1[ AuCl 4-] + k2[ AuCl 3( OH )-] + k3[ AuCl 2( OH )2-] + k4[ AuCl ( OH )3-])[ H 2 TMPyP 4+], where k1, k2, k3 and k4 were found to be (2.16 ± 0.31) × 10-1, (6.56 ± 0.19) × 10-1, (1.07 ± 0.24) × 10-1, and (0.29 ± 0.21) × 10-1 M -1. s -1, respectively. The kinetic data revealed that the trichloromonohydroxogold(III) species, [ AuCl 3( OH )]-, is the most reactive. The higher reactivity of [ AuCl 3( OH )]- is explained by hydrogen bonding formation between the hydroxyl group of [ AuCl 3( OH )]- and the pyrrole hydrogen atom of [ H 2( TMPyP )]4+. Furthermore, applying the Fuoss equation to the observed rate constants at different ionic strengths, the apparent net charge of [ H 2( TMPyP )]4+ was calculated to be +3.5.

Eine pentagonal pyramidale Koordination des Bismuts. Kristallstruktur von Methylbismutbis( diethyldithiocarbamat) / A Pentagonal Pyramidal Coordination of Bismut. Crystal Structure of Methylbismuthbis( diethyldithiocarbamate)

1979 ◽  
Vol 34 (7) ◽  
pp. 1037-1039 ◽  
Author(s):  
Christian Burschka ◽  
Markus Wieber
Keyword(s):  
Crystal Structure ◽  
Free Electron ◽  
Title Compound ◽  
Crystalline State ◽  
Electron Pair ◽  
Benzene Solution ◽  
X Ray Diffraction ◽  
X Ray ◽  
Free Electron Pair

Abstract Methylbismuth-bis(diethyldithiocarbamate), X-ray The crystal structure of the title compound, recrystallized from ethanol, was solved by means of X-ray diffraction methods and could be refined to an i?-value of 0.050 with 2126 reflections observed. In contrast to its behaviour in benzene solution, where the compound is monomeric, in the crystalline state dimeric units are formed by intermolecular Bi-S-interactions. The bismuth atoms are coordinated in form of a slightly distorted pentagonal pyramid with the free electron pair presumably directed opposite the apical C-atom.

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