Electronic Influence Of Substituents Research Articles

N-(2,2-Dimethyl-1-(quinolin-2-yl)propylidene) arylaminonickel Complexes and Their Ethylene Oligomerization.

A series of N-(2,2-dimethyl-1-(quinolin-2-yl)propylidene) arylamines was sophisticatedly synthesized and reacted with nickel(II) bromine for the formation of the corresponding nickel complexes. All the organic compounds were characterized by IR, NMR spectra and elemental analysis, while all the nickel complexes were characterized by IR spectra and elemental analysis. On activation with ethylaluminium sesquichloride (EASC) and modified methylaluminoxane (MMAO), all nickel precatalysts exhibited good activities toward ethylene oligomerization, indicating the positive efficiency of gem-dimethyl substitutents; in which major hexenes were obtained with MMAO. The catalytic parameters were verified, and the steric and electronic influences of substituents with ligands were observed, with a slight change of activities under different ethylene pressures.

Library design, synthesis and biological exploration of novel 3,4′-bicarbostyril derivatives as potent antimicrobial, antitubercular and antimalarial agents

A library comprises diversely substituted novel 3,4′-bicarbostyril derivatives have been designed by molecular hybridization technique and synthesized via multi-component reaction . Compounds G22 (MIC = 12.5 µg/mL) and G38 (MIC = 25 µg/mL) exhibited 99% inhibition against Mycobacterium tuberculosis, while compounds G40 (IC50 = 0.019 µg/mL) and G20 (IC50 = 0.028 µg/mL) found to have excellent activity against Plasmodium falciparum. Compounds G37 (MIC = 25 µg/mL) and G8, G18, and G38 (MIC = 50 µg/mL) elicited excellent antimicrobial activity compared to standard drugs. Biological results revealed that the potency of the title compounds strongly depends on the length and flexibility of various spacers at N−1, the electronic influence of substituent at R1 and lipophilicity of CH3 group at R2 position on bicarbostyril system.

Assessing Catalytic Activities Through Modeling Net Charges of Iron Complex Precatalysts

The potential activities for two series of iron complex precatalysts on ethylene reactivity are evaluated by the density functional theory (DFT)–charge equilibration (DFT–QEq) method on the basis of the molecular mechanics (MM–QEq) method. All three spin states on the central iron atom are calculated through the two charge methods to obtain the effective net charge, in addition to the QEq method alone. The results show that reasonable charge values are obtained by the QEq method, well reflecting the influence of substituents and revealing correlations between the activity and the effective net charge. All these series of iron complex precatalysts present the same tendency: the potential activities are elevated along with a decreasing effective net charge on the iron atom. Relying on the electronic influence of substituents on the ligands, the variation trends are grouped into two classes, which present the same correlation. image

Formation of the Dimer Radical Cation of Aromatic Sulfide on the TiO2 Surface during Photocatalytic Reactions

The formation of the dimer radical cation (D*+) of 4-(methylthio) benzoic acid on a TiO2 surface is demonstrated using the time-resolved diffuse reflectance technique. The observed time-resolved diffuse reflectance spectral shape significantly depends on the substrate concentrations. The substrate concentration dependences of the initial transient signal intensity (%abs.(t=0)) and the amount of adsorbates (n(ad)) clearly suggest that the formation of D*+ is attributableto the high local substrate concentration on the TiO2 surface. The electronic influence of substituents on the formation of D*+ is also discussed.

Hammett Type Correlations for Intramolecular Charge Transfer (ICT) Dipole Moments of 4’-Substituted 9-Styrylacridines in the Ground State and in the Excited State

9-Styrylacridine(1a) and a series of 4'-substituted 9-styrylacridines (1b-f) (substituent: Me, OMe, NMe 2 , Cl, NO 2 ) have been prepared to study their spectroscopic properties in several solvents of different dipolarity. They show strong Stokes shifts from the ground state to the S 1 excited state (Δ ν - 5400 to -8700 cm - 1 ) which denotes an important change of conformation in the fluorescing state. AM1 calculations suggest that the coplanarity increases in the S 1 state. The fluorescence spectra exhibit a positive solvatochromism, allowing the determination of excited state dipole moment (μ E ). Hammett correlations between σ p and μ G (ground state dipole moments) and μ E respectively, show that the electronic influence of substituent on the internal charge transfer (ICT) is ca. 3 times stronger in the S 1 excited state than in the ground state.

Studies on controlled radical polymerisation using 5-membered cyclic PROXYL nitroxides and corresponding alkoxyamines

2,2',5,5'-tetramethylpyyridine-N-oxyl (PROXYL) and derivatives bearing one α-aryl substituent (Ph, p-CF 3 Ph, p-Me 2 NPb) were prepared and converted to alkoxyamines by reaction with di-tert-butyl peroxalate (DTBPO) and excess styrene. Both the nitroxides (plus DTBPO as is radical source) and alkoxyamines were investigated in the controlled radical polymerisation (CRP) of styrene, and their behaviour was compared to that of TEMPO. Polymerization mediated by each nitroxide displayed a linear relationship between molecular weight and conversion, producing material of low polydispersity indicating a controlled process. However, a comparison of kinetic behaviour was complicated by the unknown concentration of active species present. Polymerisation with preformed alkoxyamines at a known concentration also displayed controlled behaviour (polydispersities 1.25-1.5), and an influence of nitroxide substituent on the overall rate of polymerisation could be determined. PROXYL and the dimethylanilino-substituted nitroxide gave smillar CRP rates to TEMPO, whereas a Ph or to a lesser extent p-CF 3 Ph substituent resulted in significantly faster reactions. These results are discussed in terms of the likely steric and electronic influence of substituents on the nitroxide radical centre, and the resulting influence on polymerization rate. It is concluded that the steric bulk of the Ph substituent is the most likely cause of the rate enhancement displayed by the corresponding mediator.

Evidence for Concert in the Thermal Unimolecular Vinylcyclopropane to Cyclopentene Sigmatropic 1,3-Shift

Gas phase pyrolysis of cis-2,3-dideuterio-trans-(1‘-tert-butyl-2‘-(Z)-deuteriovinyl)cyclopropane at 290 °C gives trans,trans-3,4,5-trideuterio-1-tert-butylcyclopentene as the major 1,3-shift product with greater than 90% stereospecificity in an orbital symmetry “allowed” suprafacial-inversion sense after correction for the geometric isomerization of starting material and the other materials present. The isotopic substitution at the critical sites of rearrangement eliminates steric or electronic influences of substituents on a biradical pathway as a source of the suprafacial-inversion stereochemistry observed with more highly substituted derivatives. The stereochemical results coupled with a normal deuterium kinetic isotope effect (kH/2kD = 1.14 at 311.6 °C) at the exo-methylene carbon are best interpreted in terms of a concerted pathway for rearrangement. A less likely alternative is a stereospecific disrotatory ring opening to a biradical followed by rate-determining closure to a five-membered ring. Acco...

Relative reactivities and stereochemistry for free-radical eliminations of 2-(aryloxy)-1-phenylpropyl radicals

The steric and electronic influence of substituents on the rate of addition of free radicals to multiple bonds has been much studied and reviewed. From the results of hydrogen-abstraction studies, it was expected that the ..beta..-scission reactions would exhibit substantial substituent effects. The study for which the results are reported here was undertaken to examine the effects of ..beta..-scission reactions and to gain an estimate of the energetics of ..beta..-scission. 2-(aryloxy)-1-phenylpropyl radicals generated from the reaction of the corresponding chlorides with trimethylstannane and azobisisobutyronitrile at 80/degrees/C were found to undergo reactivities for scission. This provides the first opportunity for evaluation of the steric and electronic factors that control this reaction.

13C‐NMR‐Untersuchungen an 4‐Amino‐2,6‐dialkyl‐pyrimidinen und ihren Sulfonamidderivaten

Carbon‐13 N.M.R. Studies on 4‐Amino‐2,6‐dialkyl Pyrimidines and Their Sulfonamide DerivativesCarbon‐13 n.m.r. studies on 4‐amino‐2,4‐dialkyl pyrimidines and their sulfonamide derivatives have shown that the known additivity rules for the assignment of signals are not valid. The reason is a tautomerism as demonstrated by changes of the chemical shifts of the alkyl groups. The electronic influence of substituents at the amino group on the alkyl C‐atoms are neglegible compared to changes due to tautomerism.

Influence of substituents on the chemical shift of fluorine in certain fluorosubstituted arylphenylmercury compounds and N-arylmercury derivatives of benzenesulfonanilide

1. In a comparative investigation by the19F-{1H} NMR method of a series of mono- and binuclear bridge systems containing 3- and 2-fluorophenyl indicator groups ArHgC6H4F-3(2) and ArHgN(SO2Ph)C6H4F-(2), it was established that in both types of systems the chemical shift (CS) of fluorine in the 3 position, in contrast to the CS of fluorine in the 2 position, is determined chiefly by the electronic influence of the substituents. 2. The 3-fluorophenyl indicator group in the compounds studied is less sensitive to the electronic influence of substituents than the 4-fluorophenyl group. 3. In the presence of the effects of π- or σ,π-conjugation along the bonds of the bridge atom to the aromatic ring, the comparative transmission capacity of the bridge groups may vary with changing position of the indicator group in the aromatic ring.

13C‐kernmagnetische Resonanzspektren der Phenylfulgide

Carbon‐13 Nuclear Magnetic Resonance Spectra of PhenylfulgidesThe carbon‐13 chemical shifts are determined in a series of phenylfulgides in order to investigate steric and electronic influences of substituents. By means of the shift differences between suitably substituted compounds results can be obtained as to the relative variation of the rotation angles of the phenyl rings as well as to te angle alterations between the exocyclic double bonds and the anhydride ring. Introducing 4‐CH3O‐ and 4‐NO2‐groups at the phenyl rings the substituent induced alterations of the carbon‐13 chemical shifts and the π‐polarization effects related with it are discussed.

Comparative study by the19F method of the influence of polar and coordinating solvents on the efficacy of transfer of the electronic influences of substituents in N-arylmercuri- and substituted N-benzyl derivatives of 4?-fluorobenzenesulfanilide

1. In a comparative Investigation by the19F NMR method of two series of model compounds of the type of ArQN(SO2Ph)C6H4,F-4 (Q=Hg, CH2), it was established that the Hg-N binuclear bridge grouping (BNG) possesses a greater transmission capacity (TC) than the CH2-N BNG. 2. The efficiency of the transfer of the electronic influence of substituents to an indicator F atom through the Hg-N BNG depends substantially on the direction of transmission. 3. The decrease in the TC of the Hg-N BNG in coordinating solvents is the result of both dipole-dipole and coordination interactions with the solvent the contributions of which are practically equal.

A study of the transfer of the electronic influence of substituents in o-carboranes by nuclear quadrupole resonance

The 35Cl NQR spectra of 2-substituted 1-chloromethyl-o-carboranes and of 1-chloromethyl-9,12-dihalogeno-o-carboranes have been investigated. The anomalous influence of two halogen atoms present in positions 9 and 12 of the carborane nucleus on the electron density of the chlorine atom in the CH2Cl group is explained by the combined action of their −I and +M effects, and also by the effect of p → d conjugation. The comparatively high 35Cl NQR frequency for o-ClCH2CB10H10CH is due to the large −I effect of the carboranyl group. The induction constants of a number of groups attached to the carborane ring have been evaluated. In the molecules of the 2-substituted 1-chloromethyl-o-carboranes spatial interaction between X and Cl clearly appears. The substituents X in compounds of this series can be divided into three types according to their electronic influence: 1) electron-donating substituents, 2) substituents containing a mobile hydrogen atom (capable of forming a hydrogen bond), and 3) substituents possessing an unshared pair of electrons capable of passing into the vacant 3d orbital of a chlorine atom.

Investigation of the electronic influence of substituents in the series of benzoic, butyric, and acetic acids by the Hoffman MO LCAO method

1. A quantum-chemical calculation of the molecules of a number of substituted benzoic, acetic, and butyric acids was conducted by the Hoffman MO LCAO method. 2. The charge on the carbon atom bonded to the carboxyl group changes negligibly for meta-substituted acids, while in the case of para-benzoic acids it is correlated with the MacDaniel and Brown thermodynamicσ-constants. 3. In the molecules of unbranched aliphatic acids, the electronic influence of substituents is practically quenched on the third carbon atom.