ChemInform Abstract: QUATERNARY NITROGEN HETEROCYCLES PART 5, SUBSTITUENT EFFECTS ON THE EQUILIBRIUM CONSTANTS FOR PSEUDOBASE FORMATION FROM QUINOLINIUM AND ISOQUINOLINIUM CATIONS

1974 ◽  
Vol 5 (23) ◽  
pp. no-no
Author(s):  
JOHN W. BUNTING ◽  
WILLIAM G. MEATHREL
Keyword(s):  
Equilibrium Constants ◽  
Nitrogen Heterocycles ◽  
Substituent Effects ◽  
Quaternary Nitrogen

Quaternary Nitrogen Heterocycles. V. Substituent Effects on the Equilibrium Constants for Pseudobase Formation from Quinolinium and Isoquinolinium Cations

1974 ◽  
Vol 52 (6) ◽  
pp. 962-974 ◽  
Author(s):  
John W. Bunting ◽  
William G. Meathrel
Keyword(s):  
Aqueous Solution ◽  
Magnetic Resonance ◽  
Spectral Data ◽  
Proton Magnetic Resonance ◽  
Equilibrium Constants ◽  
Nitrogen Heterocycles ◽  
Substituent Effects ◽  
Stopped Flow ◽  
Substituent Constant ◽  
Quaternary Nitrogen

Equilibrium constants (pKROH) have been measured for pseudobase formation from the 1-methyl-x-nitroquinolinium cations (x = 5–8), the N,N′-dimethyl-1,5-, -1,6-, and -2,7-naphthyridinium dications and various N-substituted quinolinium, isoquinolinium, 5-nitroisoquinolinium, and 1,8-naphthyridinium cations. The pKROH values for N-substituted 5-nitroisoquinolinium and 1,8-naphthyridinium cations are correlated by the equations pKROH = −3.7σ* + 11.6 and pKROH = −4.9σ* + 12.5, respectively (σ* is Taft's substituent constant for the substituent on nitrogen).Proton magnetic resonance and u.v. spectral data have been used to assign the structures of the pseudobases formed from each of the above cations. In several cases ylide formation rather than pseudobase formation has been observed. The N,N′-dimethylnaphthyridinium dications are shown to form zwitterionic alkoxide ions in strongly basic aqueous solution, rather than undergoing attack by a second hydroxide ion.Equilibration between cation and pseudobase occurs at rates near or beyond the limit of the stopped-flow technique for all the above cations, except the 2-cyanomethyl-5-nitroisoquinolinium cation. An analysis of the pH-rate profiles for reversible pseudobase formation from this latter cation is given.

Quaternary Nitrogen Heterocycles. I. Equilibrium and Spectral Data for Pseudobase Formation by the N-Methyl Cations of Diazanaphthalenes

1972 ◽  
Vol 50 (6) ◽  
pp. 917-931 ◽  
Author(s):  
John W. Bunting ◽  
William G. Meathrel
Keyword(s):  
Spectral Data ◽  
Ring Opening ◽  
Lithium Aluminum Hydride ◽  
Equilibrium Constants ◽  
Nitrogen Heterocycles ◽  
Aluminum Hydride ◽  
Ionization Constants ◽  
Lithium Aluminum ◽  
Quaternary Nitrogen ◽  
Hydride Reduction

Equilibrium constants have been measured at 25° for the formation of pseudobases from the 2-methyl-phthalazinium, 1-methylquinoxalinium, 1-methyl- 1,5-naphthyridinium, 6-methyl-1,6-naphthyridinium, 7-methyl-1,7-naphthyridinium, 1-methyl-1,8-naphthyridinium, 1-methyl-3-nitroquinolinium, and 2-methyl-4-nitroisoquinolinium cations. Ionization constants have also been obtained for ionization of some of these pseudobases to alkoxide anions. For each cation the site of hydroxide attack has been determined by comparison of the u.v. and p.m.r. spectra of the pseudobases, the corresponding methoxide adducts, and the lithium aluminum hydride reduction products. In all cases, except for the 1-methylquinoxalinium cation, only one major pseudobase species is present in solution, and ring-opening does not occur to any appreciable extent. The pseudobase of the 1-methylquinoxalinium cation exists in equilibrium with a considerable amount of its covalent hydrate from addition of water across the C3—N4 bond.

Quaternary Nitrogen Heterocycles. VI. Equilibria and Kinetics of Pseudobase Formation from some Heteroaromatic Dications

1974 ◽  
Vol 52 (6) ◽  
pp. 975-980 ◽  
Author(s):  
John W. Bunting ◽  
William G. Meathrel
Keyword(s):  
Equilibrium Constants ◽  
Nitrogen Heterocycles ◽  
Spectral Studies ◽  
Alkaline Solutions ◽  
Quaternary Nitrogen ◽  
Kinetics Of

Equilibrium constants (pKROH) and the kinetics of cationpseudobase equilibration have been measured for pseudobase formation by the 5,6-dihydropyrazino[1,2,3,4-lmn]-1,10-phenanthrolinium (1; pKROH = 9.54), 5H-6,7-dihydro-1,4-diazepino[1,2,3,4-lmn]-1,10-phenanthrolinium (2; pKROH = 9.17), and pyrazino[1,2,3,4-lmn]-1,10-phenanthrolinium (3; pKROH = 6.22) dications. Ultraviolet and p.m.r. spectral studies indicate that in strongly basic methanolic solutions 1 and 2 form bismethoxide adducts whereas in aqueous alkaline solutions these cations form the monopseudobase alkoxide ions (zwitterions) rather than the dipseudobases. The lower pKROH value for 2 than for 1 is suggested to arise from strain in the dication 2, which is relieved upon pseudobase formation.

Separation of the Enthalpic and Entropic Contributions to Substituent Effects for the Equilibrium Constants of Aromatic Acids

1975 ◽  
Vol 53 (23) ◽  
pp. 3622-3633 ◽  
Author(s):  
T. M. Krygowski ◽  
W. R. Fawcett
Keyword(s):  
Substituent Effect ◽  
Equilibrium Constants ◽  
Substituent Effects ◽  
Point Of View ◽  
Aromatic Acids ◽  
Resonance Effects ◽  
Equation Analysis ◽  
Reaction Constant ◽  
Enthalpy And Entropy Changes ◽  
Substituent Constants

Separation of the substituent effect ρσ into entropie ρSσS and enthalpic ρHσH contributions is presented within the framework of the general Hammett equation. Analysis of the experimental data for aromatic acids shows that, in general, entropie effects are the major contribution to the total substituent effect, the entropic reaction constant being approximately equal to the normal Hammett ρ A comparison of the present results with those based on a separation of inductive and resonance effects shows that the entropie and inductive effects are directly related. On the other hand, strongly resonance interacting substituents were found to be enthalpy controlled. The substituent effect on enthalpy and entropy changes is discussed from a molecular point of view and related to inductive and resonance effects. A list of 16 enthalpic (σH) and entropie (σS) substituent constants are presented.

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.

Kinetic and thermodynamic control of pseudobase formation from C-3 substituted 1-methylquinolinium cations

1984 ◽  
Vol 62 (7) ◽  
pp. 1301-1307 ◽  
Author(s):  
John W. Bunting ◽  
Norman P. Fitzgerald
Keyword(s):  
Aqueous Solutions ◽  
Rate Constants ◽  
Kinetic Data ◽  
Mixing Time ◽  
Equilibrium Constants ◽  
Substituent Effects ◽  
Stopped Flow ◽  
Thermodynamic Control ◽  
Preferred Species ◽  
Substituted 1

The kinetic and thermodynamic control of pseudobase formation from 3-W-1-methylquinolinium cations has been studied for a variety of substituents (W). Spectral data indicate that, in both aqueous and methanolic solution, the C-2 pseudobases predominate at equilibrium for W = H and Br, while the C-4 pseudobases are the thermodynamically preferred species for W = CONH2, CO2CH3, CN, and NO2. Stopped-flow studies indicate that in all cases the C-2 pseudobases are the kineticallycontrolled products upon basification of the aqueous solutions of these cations. Equilibrium constants (pKR+) have been measured for pseudobase formation at both C-2 and C-4 for each W in all cases where they are experimentally accessible. Substituent effects upon [Formula: see text] correlate with σm for W, while [Formula: see text] depends upon σp−. These substituent effects allow the prediction of [Formula: see text] and [Formula: see text] for the 1-methylquinolinium cation. Rates of C-2 to C-4 pseudobase equilibration have been measured in all cases where the latter species is thermodynamically more stable. These kinetic data allow the evaluation of rate constants for C-4 pseudobase equilibration with each cation. In all cases except W = CN, C-2 pseudobase formation is complete within the mixing time of the stopped-flow instrument.

scholarly journals Proton transfer equilibria, temperature and substituent effects on hydrogen bonded complexes between chloranilic acid and anilines

2000 ◽  
Vol 14 (3) ◽  
pp. 99-107 ◽  
Author(s):  
Gamal A. Gohar ◽  
Moustafa M. Habeeb
Keyword(s):  
Hydrogen Bond ◽  
Complex Formation ◽  
Proton Transfer ◽  
Equilibrium Constants ◽  
Bond Formation ◽  
Substituent Effects ◽  
Substituted Anilines ◽  
Chloranilic Acid ◽  
Hydrogen Bond Formation ◽  
Linear Relationships

The proton transfer equilibrium constants (KPT) for 1 : 1 complex formation between Chloranilic Acid (CA) and a series ofp- andm‒substituted anilines have been measured in 1,4-dioxane spectrophotometrically. The results supported the concept of amine-solvent hydrogen bond formation (short range solvation effect). Beside, this effect, theKPTvalues were apparently affected by the electron donation power of the aniline ring substituent, which was transmitted to the interaction center via resonance and inductive effects. Linear relationships betweenKPTand σ-Hammett substituent constants, or pKvalues formandpanilines,were obtained verifying the above conclusions. The solute-solvent hydrogen bond formation might increase the reactivity of the aniline nitrogen than would the inductive effect of the alkyl group, in case of CA-N-alkyl aniline complexes. The thermodynamic parameters for the proton transfer complex formation were estimated and it was indicated that the solvent–aniline hydrogen bond formation was preferred in the case ofp-substituted aniline complexes more than in the case of the correspondingm‒isomer. It has been found that the proton transfer process was enthalpy and entropy controlled.

Substituent Effects on Enthalpies of Formation of Nitrogen Heterocycles:  2-Substituted Benzimidazoles and Related Compounds

2006 ◽  
Vol 110 (7) ◽  
pp. 2535-2544 ◽  
Author(s):  
Lourdes Infantes ◽  
Otilia Mó ◽  
Manuel Yáñez ◽  
María Victoria Roux ◽  
Pilar Jiménez ◽  
...  
Keyword(s):  
Nitrogen Heterocycles ◽  
Substituent Effects ◽  
Enthalpies Of Formation ◽  
Related Compounds
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