Sites For Nucleophilic Attack Research Articles

Conjugate Addition of Alkyllithium Reagents to α,β-Unsaturated N, N',N'-Trimethylhydrazides

Abstract The site of nucleophilic attack by an alkyllithium reagent upon an α,β-unsaturated carbonyl compound is governed by, among other factors, the nature of the group attached to the carbonyl.1 Thus the amount of carbonyl addition decreases in favor of conjugate addition for the α,β-unsaturated series: aldehyde, ketone, ester, amide. We wish to report that α,β-unsaturated carboxylic acid trimethylhydrazides, which have an exceptionally unreactive carbonyl group2, undergo exclusive conjugate addition with simple alkyllithium reagents.3 Furthermore, the derived hydrazide lithium enolates can be transformed in convenient and useful ways.

Structure and reactivities of six-co-ordinate first-row transition-metal nitrosyl complexes

A molecular-orbital study of the [ML5(NO)] complexes [Fe(CN)5(NO)]2–, [Mn(CN)5(NO)]3–, and [V(CN)5-(NO)]3– as well as of the presently non-existent model compound [FeCl5(NO)]2– has been made using the INDO approximation. It has been shown that the highest occupied molecular orbital (h.o.m.o.) is an orbital of π symmetry localised on the ligands and the lowest unoccupied molecular orbital (l.u.m.o.) is a degenerate π*(MNO) orbital localised mainly on the nitrogen, but with varying amounts of metal and cis, but no trans, ligand character. Analysis of the composition of this l.u.m.o. orbital as a function of ligand electronegativity, number of electrons in the complex, and nature of the metal shows that nucleophilic attack or reduction at the nitrogen atom is favoured over the same reactions at the metal site for complexes to the right of the transition-metal series with a high formal charge on the metal. For four to six [metal d+π*(NO)] electrons the site of nucleophilic attack or reduction is independent of the number of electrons, and of the nature of the L ligand. As the L ligand becomes less electronegative the contribution of cis-ligand orbitals to the l.u.m.o. orbital increases, and it is shown that addition of electrons to the l.u.m.o. results in the expected bending of the MNO group and destabilisation of the cis M–L bond in the plane of the MNO bending. Hence, with an electropositive L ligand, loss of a cis ligand is favoured by reduction or nucleophilic attack. The energy of the l.u.m.o. decreases with the number of electrons, with increasing electro-negativity of the L ligands, and on going from left to right across the transition-metal series, making nucleophilic attack, at any site, more facile in the order given. It is shown that the trans influence of the NO ligand in these complexes cannot be measured by bond-distance data because the energy required for M–L bond-distance changes of up to 0.15 Å is extremely small. Overlap criteria cannot be used since they are dependent on the M–L distance assumed. Comparison of the total energy of [ML5(NO)], cis-[ML4(NO)], and trans-[ML4(NO)] indicates that the trans M–L bond is stronger than the cis M–L bond in [ML5(NO)] complexes.

Correlation of the reactivity of coordinated π-hydrocarbons with electronic parameters: IV. Indo molecular orbital calculations on the cations [(C 6H 5)Fe(C 5H 5)] + (X = H, Me, OMe, COOMe)

Molecular orbital calculations have been made for the series of cations [(C 6H 5X)Fe(C 5H 5)] + (X = H, Me, OMe, COOMe). The results provide some support for recent proposals concerning the relationship between the site of nucleophilic attack and the even or odd hapticity of the π-hydrocarbon ligands. However, the factors which determine the position of attack in a particular ring appear to be neither charge controlled nor influenced by the LUMO in the complex.

Reactivity of nucleophiles toward and the site of nucleophilic attack on phenyl benzenethiolsulfinate

Reactivity of nucleophiles toward and the site of nucleophilic attack on phenyl benzenethiolsulfinate

Kinetics of ligand-displacement reactions of copper(II) complexes of deprotonated linear and macrocyclic dioxotetra-amines. Comparative studies with glycylglycylglycine and glycylglycylhistidine

The kinetics of displacement of doubly deprotonated linear (X1) and 13–15-membered macrocyclic dioxotetra-amines (X2–X4), compared with glycylglycylglycine (X5) and glycylglycylhistidine (X6), from their copper(II) complexes (all commonly expressed as [CuH–2X]) have been studied with ligands of various degrees of nucleophilicity including a linear tetra-amine (L1), macrocyclic tetra-amines (L2 and L3), or ethylenediaminetetra-acetate (edta) in borate (pH 8–9.5) or lutidine buffers (pH 6–7.5). The proposed mechanisms for X1–X4 are analogous to that reported for X6, where proton assistance is needed to aid cleavage of the non-terminal copper–imide bonds and provide open sites for nucleophilic attack. The effects of cyclization of the X ligands and ring size on the relative stability of the [CuH–2X] complexes are well manifested in the ligand-replacement kinetics. Thus, the 14-membered X3 which forms the most stable complex among X1–X6 is the most inert to the substitution reactions.

ChemInform Abstract: POLAROGRAPHIC REDUCTION OF ADENINE AND ITS 9‐(α,Ω‐DIHYDROXY‐2‐ALKYL) DERIVATIVES

The polarographic reduction of adenine and its 9-(α,ω)-dihydroxy-2-alkyl) derivatives on a short-period mercury electrode in strongly acidic media is determined by the rate of diffusion of the corresponding cations and, at pH values that exceed the pKa values, by the kinetics of surface protonation of the uncharged molecules; this was proved by the dependence of the limiting current on the height of the mercury column, the temperature, and the depolarizer concentration. The polarographic reduction of adenine, adenosine, 9-(α,ω-di-hydroxy-2-alkyl)adenines, and the corresponding phosphates in acidic media proceeds with the loss of sic electrons per molecule. The similar trends of the change in the half-wave potentials and the numerical pKa values is associated with the fact that the site of protonation is simultaneously the site of nucleophilic attack by the electron during electrical reduction.

Polarographic reduction of adenine and its 9-(?,?-dihydroxy-2-alkyl) derivatives

The polarographic reduction of adenine and its 9-(α,ω)-dihydroxy-2-alkyl) derivatives on a short-period mercury electrode in strongly acidic media is determined by the rate of diffusion of the corresponding cations and, at pH values that exceed the pKa values, by the kinetics of surface protonation of the uncharged molecules; this was proved by the dependence of the limiting current on the height of the mercury column, the temperature, and the depolarizer concentration. The polarographic reduction of adenine, adenosine, 9-(α,ω-di-hydroxy-2-alkyl)adenines, and the corresponding phosphates in acidic media proceeds with the loss of sic electrons per molecule. The similar trends of the change in the half-wave potentials and the numerical pKa values is associated with the fact that the site of protonation is simultaneously the site of nucleophilic attack by the electron during electrical reduction.

Correlation of the reactivity of coordinated π-hydrocarbons with electronic parameters : II. Indo calculations on the cations [(C 7H 6X)Cr(CO) 3](X  H, OMe, COOMe)

INDO calculations show that, despite an increase in ring carbon positive charge, the decrease in reactivity of the C 7H 7 + ion towards nucleophiles upon coordination to Cr(CO) 3 can be explained in terms of increased bond index values; the site of nucleophilic attack in [(C 7H 6X)Cr(CO) 3] + (X : OMe, COOMe) systems does not in general correlate with any specific electronic parameter, and several factors may be involved.

Site of nucleophilic attack on acylpentacarbonylmanganese(I) compounds

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSite of nucleophilic attack on acylpentacarbonylmanganese(I) compoundsCharles P. Casey and Charles A. BunnellCite this: J. Am. Chem. Soc. 1976, 98, 2, 436–441Publication Date (Print):January 1, 1976Publication History Published online1 May 2002Published inissue 1 January 1976https://doi.org/10.1021/ja00418a018RIGHTS & PERMISSIONSArticle Views99Altmetric-Citations59LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (721 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

MO calculations on metal carbene complexes and metal acyl complexes. The importance of the LUMO in determining the site of nucleophilic attack

MO calculations on metal carbene complexes and metal acyl complexes. The importance of the LUMO in determining the site of nucleophilic attack

Reactions of Transition-Metal-Olefin Complexes. III. Kinetics of the Oxidation of Substituted Styrenes Catalyzed by Palladium Salts in an Aqueous Tetrahydrofuran Solution

Abstract The kinetics of the oxidation of ring-substituted styrenes catalyzed by palladium(II) salts in a homogeneous aqueous tetrahydrofuran solution containing p-benzoquinone have been investigated at 30°C under a nitrogen atmosphere. The rate equation was found to be identical with the one previously found for styrene, i.e., −d[olefin]⁄dt=(kI+kII[Pd2+][olefin], where kI is the rate constant for ketone-formation and kII is the rate constant for aldehyde-formation. It was found that both the proton and the chloride ion affect the rate inhibition at high concentrations and the rate acceleration at low concentrations. The product ratio of the ketone to the aldehyde decreased monotonously with the increase in proton concentration and with the increase in chloride ion concentration. An increase in the ionic strength from 0.052 to 0.787 increased the rate constants, but the ratio of the products scarcely changed at all. The substituent effects for the sites of nucleophilic attack were specific; i.e., the electron-releasing substituents facilitated the formation of substituted acetophenone and diminished the formation of substituted phenylacetaldehyde. The reverse trend was found for the electron-withdrawing substituents. From these results, there is proposed a mechanism in which two active species, [ArCH=CH2Pd(H2O)-(OH)Cl] and [ArCH=CH2Pd(H2O)(OH)Cl2]−, are involved and in which the rate-determining step is the decomposition of the σ-complexes with the hydride shift to the carbonyl products.

Assay of protein-quinone coupling involving compounds structurally related to the active principle of poison ivy

An experimental procedure, employing the techniques of column chromatography, has been developed by which the reactivity of waterinsoluble o-quinones toward protein can be evaluated semiquantitatively. This procedure has been used to study the effect of ring methylation on the ability of 3-pentadecyl- o-quinones to react to form protein conjugates. In this way it has been found that 3-pentadecyl- o-quinone is most reactive of all the compounds tested, whereas 4,5-dimethyl- and 4,5,6-trimethyl-3-pentadecyl- o-quinones, in which both of the normal sites for nucleophilic attack by the protein are blocked, do not react to any appreciable extent. The reactivity of all three monomethyl-3-pentadecyl- o-quinones has been found to be similar to that of the unblocked quinone, but the data for these compounds also indicate that there is some loss of reactivity resulting from steric interference by the lone methyl group in each case.