Substituent effects on the gas phase basicities of acetophenones

The gas phase basicities of m- and p-substituted acetophenones have been determined by the ion cyclotron resonance (ICR) equilibrium constant method. The application of the LArSR Eq. to these substituent effects provides a ϱ=12.2 and an r⁺=0.76 with excellent precision.     

Concerning the optimum scaling of the inductive substituent constants in substituted benzene reactivities. Aspects from the analysis of quinuclidine basicities

Grob's basicity data sets of 4-substituted quinuclidines are successfully correlated with the LArSR Eq. 1, the correlation parameters of which indicate that the inductive substituent constants involved in δ^o_p just correspond to 0.74°_I.     

Selectivity of hydrogenations. Part 4 6- and 8-substituted quinaldines yield of tetrahydroderivatives and basicities of quinolines

Hydrogenation of 6- or 8-R-substituted quinaldines [R=H, CH₃, CH(CH₃)₂, C(CH₃)₃, or CF₃] over platinum in trifluoroacetic acid gave higher yields (90%) of 5,6,7,8-tetrahydroderivatives than hydrogenation of the corresponding quinolines. ThepKa-values of 20 quinolines and quinaldines were determined by measuring the half-neutralization potentials in acetic anhydride. More basic quinolines gave higher yields of 5,6,7,8-tetrahydroproduct; exceptions are 6- and 8-methylquinoline and 8-tert. butylquinoline. Explanations for these observations are suggested.Dedicated to Prof. Dr.K. Schlögl on the occasion of his 60th birthday.     

A quantum-mechanical study of inductive and steric effects in isoalkanes

The method of “quantum mechanics of atoms in molecules” was used to find the parameters of functional groups in isopropylalkanes. The relation between such concepts of the classic theory of the structure of molecules as inductive and steric effects and electron density distribution was shown. Branching could cause deformation of the shape of an atom in a molecule accompanied by changes in volume and energy with charge conservation. The degree of damping of intramolecular steric and inductive effects was substantiated and described. An analysis of transferability of groups and the corresponding parameters was performed to obtain procedures for calculating properties by additive methods.     

Preparative separation of quinolines by centrifugal partition chromatography with gradient elution

Centrifugal partition chromatography has been successfully applied to the separation of 2-alkylquinolines from liquid combinatorial synthesis crude samples. Original gradient elution using the ternary two-phase solvent systems heptane-water-acetonitrile and heptane-acetonitrile-methanol were used to separate them with high purity degrees. Part of the effluent was monitored with evaporative light scattering detection, for direct control, and the collected fractions were analyzed by thin-layer chromatography, GC, nuclear magnetic resonance spectroscopy and MS. It was thus possible to purify in one run more than 3 g of crude mixture using only 1.31 of solvents to obtain more than 300 mg of several alkylquinolines homologues with 99% purity and in less than 7 h.     

Substituent effects on the gas phase basicities of methyl benzoates. Effects of resonance demand on susbtituent effects

The gas phase basicities of m,p-substituted methyl benzoates have been determined by means of the pulsed ICR mass spectrometer. LArSR analysis of the subtituent effect provides a smaller r⁺ of 0.45 compared to that of acetophenone basicities, indicating a reduced resonance demand of the conjugate acid ion of methyl benzoate.     

Steric effects of substituted quinolines on lithium coordination geometry

The X-ray crystal structures of a series of lithium quinolates – lithium 8-hydroxyquinolinate (Liq), lithium 2-methyl-8-hydroxyquinolinate (MeLiq), and 2-phenyl-8-hydroxquinolinate (PhLiq), are compared. The substitution at the 2-position of the 8-hydroxyquinoline ligand has significant impact on the aggregation of the lithium complex in the crystalline state. Liq and MeLiq molecules crystallize as hexamers, whereas PhLiq crystallizes as a tetramer. The possible influence of crystal-packing forces on the preferred cluster structure was probed using density functional theory calculations on a systematically varied set of Liq, MeLiq, and PhLiq clusters. For Liq and MeLiq, the observed structures match the most stable computed structures. In the PhLiq case, the observed tetrameric structure is computed to be less stable (+1.2 kcal/mol/monomer) than the lowest energy structure, a hexamer. In this case, solid-state effects probably outweigh small differences in cluster stability.     

Magnitudes of the inductive effects of the nitro and nitrate groups

Conclusions The value of the induction constant for the nitrate group has been calculated (^*(–CH₂ONO₂)=1.34) and the value of the induction constant of the nitro group has been refined (^*(–CH₂NO₂)=1.73).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1488–1490, August, 1966.     

Geometrical substituent parameters for benzene derivatives: inductive and resonance effects

A full set of geometrical parameters describing the effect of 21 substituents on the internal angles of the benzene ring has been derived by linear regression from many structural results. The parameters are shown to reflect the inductive and resonance effects of the substituents.     

A general Poisson-Boltzmann model with position-dependent dielectric permittivity for electric double layer analysis

In this paper, we propose a general Poisson-Boltzmann model for electric double layer (EDL) analysis with the position dependence of dielectric permittivity considered. This model provides physically reasonable property profiles in the EDL region, and it is then utilized to investigate the depletion layer effect on EDL structure and interaction near hydrophobic surfaces. Our results show that both the electric potential and the interaction pressure between surfaces decrease due to the lower permittivity in the depletion layer. The reduction becomes more profound at larger variation magnitude and range. This trend is in general agreement with that observed from the previous stepwise model; however, that model has overestimated the influence of permittivity variation effect. For the thin depletion layer and the relative thick EDL, our calculation indicates that the permittivity variation effect on EDL usually can be neglected. Furthermore, our model can be readily extended to study the permittivity variation in EDL due to ion accumulation and hydration in the EDL region.     

An efficient catalytic system for the hydrogenation of quinolines

A new catalytic system ([Ru(p-cymene)Cl₂]₂/I₂) has been developed for the hydrogenation of quinoline derivatives with high reactivity. For the 2-methyl-quinoline, the hydrogenation reaction can proceed smoothly at an S/C of 20,000/1 with complete conversion. The iodine additive is important for the reactivity.     

A mild and efficient one-step synthesis of quinolines

[reaction: see text] The Friedl?nder synthesis of quinolines is an extensively employed protocol, yielding the desired heterocycle in a two-step reduction-condensation sequence. We have developed a mild, efficient, high-yielding single-step variant of this methodology, which employs SnCl(2) and ZnCl(2) to effect the reaction.     

A simple synthesis of trisubstituted quinolines through transesterification

An efficient and simple method has been reported for the synthesis of 2,3,4‐trisubstituted quinolines through zwitterion intermediate under reflux condition in presence of sulfuric acid. The formed dicarboxylate subsequently undergoes transesterification in various alcohols with good yields. Most of the synthesized compounds are newly reported characterized by spectroscopic method. J. Heterocyclic Chem., (2011).     

A mild and efficient one-step synthesis of quinolines

2-Aminoaryl ketones undergo condensation with α-methylene ketones in the presence of a catalytic amount of Y(OTf)₃ at room temperature under mild conditions to afford the corresponding polysubstituted quinolines in excellent yields.     

Facile one-pot method for the synthesis of novel glycosylidene-based quinolines

A one-pot approach to the synthesis of novel glycosylidene-based quinolines is described. The reaction involves a Lewis acid catalyzed Povarov addition followed by oxidation of the resulting spiroanellated tetrahydroquinoline intermediates to yield the open-ring glycosylidene-derived quinoline.     

CNDO/2 calculations on the relative basicities of alkyl benzenes

CNDO/2 calculations were performed for toluene, ethyl benzene, iso-propyl benzene, t-butyl benzene, and neo-pentyl benzene, and the corresponding ortho, meta, and para protonated species. All rotational conformers against the benzene ring were examined and detailed energy differences and charge analyses are presented and discussed. The calculated energy differences suggest that for gas phase species the order of alkyl substituent rate enhancement for electrophilic aromatic reactions is t-Bu>i-Pr>Et>Me>H, thus the inductive order is found, rather than the hyperconjugative or Baker-Nathan order.     

The connection between the ionization constants of alkaloids and their basicities

Summary 1. The pK_a values of a number of indole alkaloids ofVinca erecta in aqueous ethanolic solution and in chloroform have been determined.2. It has been shown that the pK_a value of an alkaloid in water or in chloroform is not connected with the pH of the transition from chloroform into a buffer solution.3. It is impossible to estimate the basicity of an alkaloid from its pK_a value.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 57–59, January–February, 1973.     

Comparative basicities of substituted pyridines and electronegativity series for substituents in the pyridine series

Relationships between basicity of the pyridine ring and the nature and position of substituents are found. Comparative electronegativity series are constructed for substituents (, , and ) in the pyridine series. In isolated cases transmission of an effect from the position by a M effect is found.