Addition-elimination Mechanism Research Articles

Phosphonylation and aging mechanisms of mipafox and butyrylcholinesterase: A theoretical study

Phosphonylation and aging processes between butyrylcholinesterase with mipafox have been studied at the B3LYP/6-311G(d,p) level of theory. The calculated results indicate that the phosphonylation process employs a two-step addition-elimination mechanism with the addition (the first step) as the rate-limiting step. Two different calculation models revealed that the catalytic triad of butyrylcholinesterase plays an important role in accelerating the reaction. This is the same mechanism as the phosphonylation reaction of acetylcholinesterase by sarin reported by Wang et al. However, the energy barrier of the rate-limiting step in the present reaction is higher than that in phosphonylation reaction of acetylcholinesterase by sarin. This indicates the differences in the phosphonylation activity of sarin and mipafox. The aging process occurs through a two-step addition-elimination mechanism similar to the phosphonylation process with the addition as the rate-limiting step. The solvent effects have been evaluated by using a CPCM model and the results show that the stationary structures and the negative charges around some important atoms involved in the two processes are not significantly different. However, the energy barrier of the phosphonylation process is remarkably decreased, revealing that this process is feasible in solution.

Modular Palladium Bipyrazoles for the Isomerization of Allylbenzenes – Mechanistic Considerations and Insights into Catalyst Design and Activity, Role of Solvent, and Additive Effects

AbstractThe catalytic activity of novel bidentate N,N‐chelated palladium complexes derived from electron excessive, backbone fused 3,3′‐bipyrazoles in the selective isomerization of terminal arylpropenoids and 1‐alkenes is described. The catalysts are easily modified by appropriate wing tip substitution, while maintaining the same bulky, rigid unreactive aliphatic backbone. Eleven novel palladium complexes with different electronic and steric properties were investigated. Their performance in the palladium(II)‐catalyzed isomerization of a series of substituted allylbenzenes was evaluated in terms of electronic as well as steric effects. Besides the clear finding of a general trend towards higher catalyst activity with more electron‐donating properties of the coordinated N,N‐bidentate ligands, we found that the catalytic process strongly depends on the choice of solvents and additives. Extensive solvent screening revealed that reactions run best in a 2:1 toluene‐methanol mixture, with the alcohol employed being a crucial factor in terms of electronic and steric factors. A reaction mechanism involving a hydride addition–elimination mechanism starting with a palladium hydride species generated in situ in alcoholic solutions, as corroborated by experiments using deuterium labeled allylbenzene, seems to be most likely. The proposed mechanism is also supported by the observed reaction rate orders of κobs[cat.]≈1 (0.94), κobs [substrate]=0.20→1.0 (t→∞) and κobs [methanol]=−0.51 for the isomerization of allylbenzene. Furthermore, the influence of acid and base, as well as the role of the halide coordinated to the catalyst, are discussed. The system catalyzes the isomerization of allylbenzenes very efficiently yielding high E:Z selectivities under very mild conditions (room temperature) and at low catalyst loadings of 1 mol% palladium even in unpurified solvents. The integrity and stability of the catalyst system were confirmed by multiple addition reaction cycles, successive filtration and isolation experiments, and the lack of palladium black formation.

On the role of Cys150 in the mechanism of maleamate amidohydrolase (NicF)

The oxidative degradation of nicotinate (vitamin B3) to fumarate is considered a model system for the bacterial degradation of N‐heterocyclic compounds, yet only recently has the complete set of genes corresponding to the enzymes involved in this pathway been identified. The identification of these six genes has enabled structural and functional analyses of the enzymes of this catabolic pathway to be undertaken. Maleamate amidohydrolase (NicF), catalyzes the penultimate reaction of the pathway ‐ the hydrolytic deamination of maleamate to maleate. The crystal structure of NicF, determined at 2.4 Å using molecular replacement, shows that the enzyme belongs to the cysteine hydrolase superfamily. The crystal structure offers insight into the roles of potential catalytically important residues, notably a conserved triad (Asp29, Lys117, Cys150) hypothesized to catalyze an addition‐elimination mechanism. In an effort to examine the functional importance of Cys150 in the mechanism iodoacetamide was discovered to be a potent inactivator. To test whether inhibition of NicF by sulfhydryl blocking reagents is reversible a study with methyl methanethiolsulfonate (MMTS) will be conducted. In addition, results of the kinetic analyses of NicF variants, Cys150Ser/Ala and Asp29Asn/Ala, are reported. This work was supported by a HHMI Undergraduate Science Education Program Award to the College of Wooster.

Switching Pathways: Room‐Temperature Neutral Solvolysis and Substitution of Amides

Stick or twist: By introducing steric hindrance at the nitrogen atom, stable linear amides bearing an electron-withdrawing α-substituent (Z = Ar, PhSO(2), P(O)(OR)(2), CN, or CO(2)R) can be induced to undergo solvolysis and substitution reactions through an elimination-addition mechanism (see picture). Key to this process is a low barrier to rotation around the amide bond and the α-substituent Z.

Base-Promoted Selective Aryl C–Cl Cleavage by Iridium(III) Porphyrins via a Metalloradical Ipso Addition–Elimination Mechanism

Base-promoted aryl carbon–chlorine bond (Ar–Cl) cleavage by iridium(III) porphyrin carbonyl chloride (IrIII(ttp)(CO)Cl; ttp = 5,10,15,20-tetrakis(p-tolyl)porphyrinato dianion) was achieved in the presence of K2CO3 to give iridium(III) porphyrin aryls (IrIII(ttp)Ar). Mechanistic studies revealed that K2CO3 promotes the reduction of Ir(ttp)(CO)Cl to give the iridium(II) porphyrin dimer intermediate [IrII(ttp)]2. [Ir(ttp)]2 is the source of IrII(ttp) metalloradical, which cleaves Ar–Cl to give Ir(ttp)Ar and a chlorine radical (Cl•) via radical ipso substitution in an addition–elimination pathway. Cl• reacts with [Ir(ttp)]2 to yield Ir(ttp)Cl for subsequent base-promoted reduction and Ir(ttp) for radical chain propagation. Additionally, the base-promoted Ar–Cl cleavage of chlorobenzene (PhCl) by Ir(ttp)(CO)Cl gives both Ir(ttp)Ph and 1,4-bis-iridium(III)-porphyrin benzene, IrIII(ttp)(p-C6H4)IrIII(ttp). The reactive Cl• can simultaneously react with PhCl via homolytic aromatic substitution to give 1,4-dichlorobenzene, which further undergoes double Ar–Cl cleavage to form Ir(ttp)(p-C6H4)Ir(ttp).

Detailed Analysis for the Solvolysis of Isopropenyl Chloroformate.

The specific rates of solvolysis (including those obtained from the literature) of isopropenyl chloroformate (1) are analyzed using the extended Grunwald-Winstein equation, involving the N(T) scale of solvent nucleophilicity (S-methyldibenzothiophenium ion) combined with a Y(Cl) scale based on 1-adamantyl chloride solvolysis. A similarity model approach, using phenyl chloroformate solvolyses for comparison, indicated a dominant bimolecular carbonyl-addition mechanism for the solvolyses of 1 in all solvents except 97% 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP). An extensive evaluation of the outcomes acquired through the application of the extended Grunwald-Winstein equation resulted in the proposal of an addition-elimination mechanism dominating in most of the solvents, but in 97-70% HFIP, and 97% 2,2,2-trifluoroethanol (TFE), it is proposed that a superimposed unimolecular (S(N)1) type ionization is making a significant contribution.

Reactivity and selectivity of charged phenyl radicals toward amino acids in a Fourier transform ion cyclotron resonance mass spectrometer.

The reactivity of 10 charged phenyl radicals toward several amino acids was examined in the gas phase in a dual-cell Fourier transform ion cyclotron resonance mass spectrometer. All radicals abstract a hydrogen atom from the amino acids, as expected. The most electrophilic radicals (with the greatest calculated vertical electron affinities (EA) at the radical site) also react with these amino acids via NH(2) abstraction (a nonradical nucleophilic addition-elimination reaction). Both the radical (hydrogen atom abstraction) and nonradical (NH(2) abstraction) reaction efficiencies were found to increase with the electrophilicity (EA) of the radical. However, NH(2) abstraction is more strongly influenced by EA. In contrast to an earlier report, the ionization energies of the amino acids do not appear to play a general reactivity-controlling role. Studies using several partially deuterium-labeled amino acids revealed that abstraction of a hydrogen atom from the α-carbon is only preferred for glycine; for the other amino acids, a hydrogen atom is preferentially abstracted from the side chain. The electrophilicity of the radicals does not appear to have a major influence on the site from which the hydrogen atom is abstracted. Hence, the regioselectivity of hydrogen atom abstraction appears to be independent of the structure of the radical but dependent on the structure of the amino acid. Surprisingly, abstraction of two hydrogen atoms was observed for the N-(3-nitro-5-dehydrophenyl)pyridinium radical, indicating that substituents on the radical not only influence the EA of the radical but also can be involved in the reaction. In disagreement with an earlier report, proline was found to display several unprecedented reaction pathways that likely do not proceed via a radical mechanism but rather by a nucleophilic addition-elimination mechanism. Both NH(2) and (15)NH(2) groups were abstracted from lysine labeled with (15)N on the side chain, indicating that NH(2) abstraction occurs both from the amino terminus and from the side chain. Quantum chemical calculations were employed to obtain insights into some of the reaction mechanisms.

Mechanistic Evaluation of MelA α-Galactosidase from Citrobacter freundii: A Family 4 Glycosyl Hydrolase in Which Oxidation Is Rate-Limiting

The MelA gene from Citrobacter freundii, which encodes a glycosyl hydrolase family 4 (GH4) α-galactosidase, has been cloned and expressed in Escherichia coli. The recombinant enzyme catalyzes the hydrolysis of phenyl α-galactosides via a redox elimination-addition mechanism involving oxidation of the hydroxyl group at C-3 and elimination of phenol across the C-1-C-2 bond to give an enzyme-bound glycal intermediate. For optimal activity, the MelA enzyme requires two cofactors, NAD(+) and Mn(2+), and the addition of a reducing agent, such as mercaptoethanol. To delineate the mechanism of action for this GH4 enzyme, we measured leaving group effects, and the derived β(lg) values on V and V/K are indistinguishable from zero (-0.01 ± 0.02 and 0.02 ± 0.04, respectively). Deuterium kinetic isotope effects (KIEs) were measured for the weakly activated substrate phenyl α-D-galactopyranoside in which isotopic substitution was incorporated at C-1, C-2, or C-3. KIEs of 1.06 ± 0.07, 0.91 ± 0.04, and 1.02 ± 0.06 were measured on V for the 1-(2)H, 2-(2)H, and 3-(2)H isotopic substrates, respectively. The corresponding values on V/K were 1.13 ± 0.07, 1.74 ± 0.06, and 1.74 ± 0.05, respectively. To determine if the KIEs report on a single step or on a virtual transition state, we measured KIEs using doubly deuterated substrates. The measured (D)V/K KIEs for MelA-catalyzed hydrolysis of phenyl α-D-galactopyranoside on the dideuterated substrates, (D)V/K((3-D)/(2-D,3-D)) and (D)V/K((2-D)/(2-D,3-D)), are 1.71 ± 0.12 and 1.71 ± 0.13, respectively. In addition, the corresponding values on V, (D)V((3-D)/(2-D,3-D)) and (D)V((2-D)/(2-D,3-D)), are 0.91 ± 0.06 and 1.01 ± 0.06, respectively. These observations are consistent with oxidation at C-3, which occurs via the transfer of a hydride to the on-board NAD(+), being concerted with proton removal at C-2 and the fact that this step is the first irreversible step for the MelA α-galactosidase-catalyzed reactions of aryl substrates. In addition, the rate-limiting step for V(max) must come after this irreversible step in the reaction mechanism.

Experimental and Theoretical Investigation of the Kinetics of the Reaction of Atomic Chlorine with 1,4-Dioxane

The rate coefficients for the reaction of 1,4-dioxane with atomic chlorine were measured from T = 292-360 K using the relative rate method. The reference reactant was isobutane and the experiments were made in argon with atomic chlorine produced by photolysis of small concentrations of Cl2. The rate coefficients were put on an absolute basis by using the published temperature dependence of the absolute rate coefficients for the reference reaction. The rate coefficients for the reaction of Cl with 1,4-dioxane were found to be independent of total pressure from p = 290 to 782 Torr. The experimentally measured rate coefficients showed a weak temperature dependence, given by k(exp)(T) = (8.4(-2.3)(+3.1)) × 10(-10) exp(-(470 ± 110)/(T/K)) cm3 molecule (-1) s(-1). The experimental results are rationalized in terms of statistical rate theory on the basis of molecular data obtained from quantum-chemical calculations. Molecular geometries and frequencies were obtained from MP2/aug-cc-pVDZ calculations, while single-point energies of the stationary points were computed at CCSD(T) level of theory. The calculations indicate that the reaction proceeds by an overall exothermic addition-elimination mechanism via two intermediates, where the rate-determining step is the initial barrier-less association reaction between the chlorine atom and the chair conformer of 1,4-dioxane. This is in contrast to the Br plus 1,4-dioxane reaction studied earlier, where the rate-determining step is a chair-to-boat conformational change of the bromine-dioxane adduct, which is necessary for this reaction to proceed. The remarkable difference in the kinetic behavior of the reactions of 1,4-dioxane with these two halogen atoms can be consistently explained by this change in the reaction mechanism.

Theoretical Study of the Decomposition of BCl3 Induced by a H Radical

We report on a theoretical study of the gas-phase decomposition of boron trichloride in the presence of hydrogen radicals using ab initio energetic calculations coupled to TST, RRKM, and VTST-VRC kinetic calculations. In particular, we present an addition-elimination mechanism (BCl(3) + H → BHCl(2) + Cl) allowing for a much more rapid consumption of BCl(3) than the direct abstraction reaction (BCl(3) + H → BCl(2) + HCl) considered up to now. At low temperatures, T ≤ 800 K, our results show that a weakly stabilized complex BHCl(3) is formed with a kinetic law compatible with the consumption rate measured in the former experiments. At higher temperatures, this complex is not stable and then easily eliminates a chlorine atom. Our work also shows that a very similar mechanism, involving the same intermediate and sharing the same transition state, allows for the elimination of HCl. A dividing coefficient between these two elimination pathways is obtained from both a potential energy surface based statistical analysis and an ab initio molecular dynamics transition path sampling simulation. It finally allows partitioning of the global consumption rate of BCl(3) in terms of the formation of (i) BHCl(3), (ii) BHCl(2) + Cl through a H addition/Cl elimination mechanism, (iii) BCl(2) + HCl through a H addition/HCl elimination mechanism, and (iv) BCl(2) + HCl through direct abstraction.

Theoretical Analysis of the Detailed Mechanism of Native Chemical Ligation Reactions

The method of native chemical ligation between an unprotected peptide α-thioester and an N-terminal cysteine-peptide to give a native peptide in aqueous solution is one of the most effective peptide ligation methods. In this work, a systematic theoretical study was carried out to fully understand the detailed mechanism of ligation. It was found that for the conventional native chemical ligation reaction between a peptide thioalkyl ester and a cysteine in combination with an added aryl thiol as catalyst, both the thiol-thioester exchange step and the transthioesterification step proceed by an anionic concerted S(N)2 displacement mechanism, whereas the intramolecular rearrangement proceeds by an addition-elimination mechanism, and the rate-limiting step is the thiol-thioester exchange step. The theoretical method was then extended to study the detailed mechanism of the auxiliary-mediated peptide ligation between a peptide thiophenyl ester and an N-2-mercaptobenzyl peptide in which both the thiol-thioester exchange step and intramolecular acyl-transfer step proceed by a concerted S(N)2-type displacement mechanism. The energy barrier of the thiol-thioester exchange step depends on the side-chain steric hindrance of the C-terminal amino acid, whereas that of the acyl-transfer step depends on the side-chain steric hindrance of the N-terminal amino acid.

Basic hydrolysis of quinolinyl N,N‐dimethylcarbamates: a two‐step mechanism

AbstractThe reactivity of 6‐quinolinyl and 8‐quinolinyl N,N‐dimethylcarbamates was examined in several aqueous basic media. A quadratic dependence was observed for the constant rates upon hydroxide concentration for both compounds, which is a typical behaviour of a mechanism involving a base‐catalysed deprotonation of the tetrahedral intermediate with the formation of a dianion at high concentrations of hydroxide ion, while at lower concentrations a specific‐base catalysed addition–elimination mechanism seems to be predominant. The reactivity of 8‐quinolinyl N,N‐dimethylcarbamate was also studied in several amine buffers, showing specific base catalysis. The reactivity of 6‐quinolinyl N,N‐dimethylcarbamate was studied in H2O and in D2O and the solvent isotope effect supports the proposal of a mechanism involving a specific‐base hydrolysis. All results confirm the existence of a mechanism with a rate determining step involving the substrate anion and a second mole of hydroxide ion. This mechanism was so far unknown for carbamate reactivity, being only known to occur with amides. Copyright © 2011 John Wiley & Sons, Ltd.

Design, synthesis and evaluation of 3-methylene-substituted indolinones as antimalarials

The design, synthesis and evaluation of 3-methylene-substituted indolinones as falcipain inhibitors and antiplasmodial agents are described. These compounds react readily with thiols via an addition-elimination mechanism, indicating their potential as cysteine protease inhibitors. Several indolinones containing a Leu-i-amyl recognition moiety were found to be moderate inhibitors of the Plasmodium falciparum cysteine protease falcipain-2, but not of the related protease falcipain-3, and displayed antiplasmodial activity against the chloroquine-resistant P. falciparum W2 strain in the low micromolar range. Coupling a 7-chloroquinoline moiety to the 3-methylene-substituted indolinone scaffold led to a significant improvement in antiplasmodial activity.

DFT and ab initio theoretical study for the CF 3S + CO reaction

The potential energy surface for the reaction of CF 3S with CO is calculated at the G4//B3LYP/6–311++G(d,p) level of theory. The results show that F-abstraction and addition–elimination mechanisms are involved, and the latter one is dominant thermodynamically and kinetically. The dominant channel is the reactant addition to form CF 3SCO, and then decomposes to CF 3 + OCS. While the direct F-abstraction channel and CF 3SCO isomerization channel are not significant for the title reaction due to higher barriers involved. The comparisons among four reactions of C X 3 Y + CO ( X = H, F; and Y = O, S) are made to imply the similar and different properties and reactivities of the same family elements and the F- and S-substituted derivatives.

A theoretical analysis of the kinetics of the reaction of atomic bromine with tetrahydrofuran

The kinetic behaviour for the reaction of atomic bromine with tetrahydrofuran has been analysed using the information from quantum chemical calculations. Structures and energy profiles were first obtained using density functional theory (DFT) employing the Dunning’s basis sets of triple-zeta quality, and then for an accurate energetic description, single-point calculations were carried out at the coupled-cluster with single and double excitations (CCSD) and the fourth-order Møller–Plesset (MP4(SDQ)) levels of theory. The rate coefficients and the equilibrium constants for the potential reaction channels were obtained from the statistical rate theories and statistical thermodynamics, respectively, using the results of quantum chemical calculations; and the results were compared with our recently published experimental data. In terms of reaction mechanism, this reaction was found to be analogous to the reactions of the Br atom with 1,4-dioxane and with methanol, where the reaction proceeds via an addition–elimination mechanism. The dominant reaction channel involved coordination of the approaching Br atom to one of the hydrogen atoms adjacent to the ether oxygen atom, i.e., β-hydrogen abstraction is uncompetitive. Although the complexes formed by direct coordination of the Br atom to the ether oxygen atom appeared in the reaction mechanism, we were not able to link them specifically to any reaction. The density functional theory predicted an activation energy and enthalpy of reaction that were much smaller than the experimental values, which led to an overestimation of the theoretical rate coefficients. The source of this discrepancy could be attributed to the overbinding of the transition states and of the tetrahydrofuranyl radical by DFT. Single-point calculations at the DFT structures using the CCSD and MP4(SDQ) methods yielded an accurate energetic description of the reaction of tetrahydrofuran with bromine, resulting in rate coefficients that showed excellent agreement with the experimental values.

ChemInform Abstract: The Kinetics and Mechanism of the Thallium(III) Ion Promoted Hydrolysis of Thiolurethanes in Aqueous Solution. A Metal Ion Promoted Elimination.

The hydrolysis of thiolurethanes R1C6H4NHCOSC6H4R2(1), in dilute aqueous perchloric acid, under conditions where the spontaneous hydrolysis is negligible, is promoted by Tl3+ ions. The organic products are the corresponding anilinium ion and the thallium salt of the thiophenol. The effects of substituent changes (R1,R2) of changes in [H3O+], temperature, ionic strength, and of replacement of the NH proton by Me, are all compatible with hydrolysis occurring by elimination–addition mechanisms via the isocyanate as a reactive intermediate; thallium ion-promoted E1 cb and E2 routes are implicated. In effect the elimination–addition type of mechanism which is important for these esters at higher pH has been made available at low pH by complexation with Tl3+ ions. With the thiolurethanes RC6H4NHCOSEt, (2) which are less susceptible to the sponataneous and base-catalysed elimination–addition mechanisms of hydrolysis than are thiolurethanes (1), the presence of Tl3+ ions can also lead to promoted hydrolysis via elimination, but an AAC1-like route (with Tl3+ taking the role of H+) seems to be available to the N-Me derivatives.

ChemInform Abstract: Stereochemical Aspects on the Formation of Chiral Allenes from Propargylic Ethers and Epoxides

Chiral propargylic ethers react with organocopper reagents to afford optically active allenes by a u addition to the triple bond followed by an anti p- elimination of the resulting alkenyl copper species. However, the same reaction, run with a Grignard reagent and a catalytic amount of copper (I) salt affords allenes through an anti or svn process. The crucial step is the p-elimination of the intermediate alkenyl metal species, which is of & type with FWa and of type with RMgCJ. Propargylic acetates, which also afford allenes in this reaction, but through a Cu(II1) intermediate, are not sensitive to this halogen effect. By close analogy to ethers, propargylic epoxides react with Grignard reagents and catalytic amount of Cu(1) salt, leading to a-allenic alcohols. The reaction is highly diastereoselective and its stereochemical outcome can be fully controlled.The diastereomer, probably arising through an addition-elimination mechanism, is better obtained with RM&l and copper (I) bromide, whereas the anti diastereomer is best obtained with RM& and a complexed copper (I) salt.

ChemInform Abstract: 1,2-Carbamoyl Migration on Enantio-Enriched α-Lithioalkyl Carbamates Generated with s-Butyllithium/Sparteine: Steric Course and Mechanism.

Alkyl N,N-diisopropylcarbamates, when lithiated with s-BuLi/(−)-sparteine in ether at −78 °C followed by warming to room temperature, are shown to undergo the 1,2-carbamoyl migration to give the α-hydroxy amides in >95% ee with complete retention of configuration at the Li-bearing carbanion terminus. An addition-elimination mechanism is proposed.

H-Atom Yields from the Photolysis of Acetylene and from the Reaction of C2H with H2, C2H2, and C2H4

The photolysis of acetylene at 193 nm has been investigated as a source of the ethynyl radical, C(2)H, for product branching ratio studies, particularly the formation of H atom product as the photolysis, producing a 1:1 ratio of C(2)H and H, provides an internal calibration. Previous literature had suggested that C(2)H and H may only be a minor component of acetylene photolysis at 193 nm. Acetylene was photolyzed at low laser energy densities (<7 mJ cm(-2)), with H atoms being observed as a function of time by VUV laser induced fluorescence. When C(2)H was reacted with C(2)H(2), a reaction that is known to produce H atoms with unit yield, the ratio of photolytic H atom production to chemical production was 0.96 +/- 0.03. The rate coefficient for the reaction of C(2)H with C(2)H(2) could accurately be retrieved from the time evolution of the H atom signal. The results suggest that acetylene photolysis at low laser energies is a good source of C(2)H for product branching studies, and the technique has been applied to the reactions of C(2)H with ethene and propene. For the reaction with ethene between 23 and 81 Torr, the yield of H is 0.94 +/- 0.06, suggesting that an addition elimination mechanism dominates with the formation of vinylacetylene and H atoms. For the reaction of C(2)H with propene, no H atom product was observed, putting a lower limit of <5% for H atom production. Possible explanations for the low H atom yield are discussed. The implications of these results in combustion and planetary atmospheres are briefly considered.

SN2’ versus SN2 Reactivity: Control of Regioselectivity in Conversions of Baylis-Hillman Adducts

TiCl(4)-induced Baylis-Hillman reactions of alpha,beta-unsaturated carbonyl compounds with aldehydes yield the (Z)-2-(chloromethyl)vinyl carbonyl compounds 5, which react with 1,4-diazabicyclo[2.2.2]octane (DABCO), quinuclidine, and pyridines to give the allylammonium ions 6. Their combination with less than one equivalent of the potassium salts of stabilized carbanions (e.g. malonate) yields methylene derivatives 8 under kinetically controlled conditions (S(N)2' reactions). When more than one equivalent of the carbanions is used, a second S(N)2' reaction converts 8 into their thermodynamically more stable allyl isomers 9. The second-order rate constants for the reactions of 6 with carbanions have been determined photometrically in DMSO. With these rate constants and the previously reported nucleophile-specific parameters N and s for the stabilized carbanions, the correlation log k (20 degrees C)=s(N + E) allowed us to calculate the electrophilicity parameters E for the allylammonium ions 6 (-19 < E < -18). The kinetic data indicate the S(N)2' reactions to proceed via an addition-elimination mechanism with a rate-determining addition step.