Acetonitrile Exchange Research Articles

Rapid, sensitive, and reliable quantitation of nicotine and its main metabolites cotinine and trans-3′-hydroxycotinine by LC-MS/MS: Method development and validation for human plasma

New nicotine delivery products are gaining market share. For evaluation of their characteristics, toxicokinetic investigations are in current research focus. For reliable determination of blood plasma levels of nicotine and its main metabolites cotinine and trans-3′-hydroxycotinine, a quantitation method based on LC-ESI-MS/MS was developed and validated. Addition of isotope labeled internal standards prior to rapid sample preparation using protein precipitation with methanol was chosen for sample preparation. Different stationary phases were tested and phenyl-hexyl separation was found to be superior to HILIC, C18, and C8 stationary phases. Ion suppression effects caused by hydrophilic early eluting matrix were eliminated by the adjustment of an adequate retention utilizing a phenyl-hexyl separation stationary phase. Exchange of acetonitrile as organic mobile phase by methanol and elevation of pH value of aqueous mobile phase containing 5 mM NH4Ac to 4.50 improved the chromatographic resolution. The limits of quantitation for nicotine, cotinine, and hydroxycotinine were 0.15, 0.30, and 0.40 ng/mL, respectively. Linearity was proven by matrix matched calibration for the whole working range from 0.50 ng/mL to 35.0 ng/mL for nicotine and from 6.00 to 420 ng/mL for cotinine and hydroxycotinine (Mandel’s fitting test with R2 > 0.995). Quality control samples at four different levels (0.50, 1.50, 17.5, 28.0 ng/mL for nicotine and 6.00, 18.0, 210, 336 ng/mL for cotinine and hydroxycotinine) in plasma were analyzed six times on three days. Mean accuracies ranged from 87.7% to 105.8% for nicotine, from 90.3% to 102.9% for cotinine, and from 99.9% to 109.9% for hydroxycotinine. Intra- and inter-day precisions (RSD %) were below 15% for all analytes (<20% for LLOQ). As proof of concept, the method was successfully applied to a real plasma sample from a cigarette smoking volunteer.

A straightforward synthesis of cationic nitrile ligated transition metal complexes with the [B(C 6F 5) 4] − anion

Nitrile ligated transition metal complexes bearing polyfluorinated tetra(aryl)borates as counter anions are highly active initiators/mediators for various polymerization reactions. However, the methods for their preparation are still far too inefficient for widespread use in applied research or in industry. Accordingly, an improved synthesis for two of the most promising species in this assemblage of complexes, namely [Cu(C 6H 5CN) 5][B(C 6F 5) 4] 2 and [Zn(CH 3CN) 4/6][B(C 6F 5) 4] 2, has been developed. This route provides easy access to pure products on a gram scale, by the reaction of copper(II)acetate and diethyl zinc with [H(OEt 2) 2][B(C 6F 5) 4]. Additionally, a new route for the synthesis of the oxonium acid as precursor has been developed, allowing a fast preparation of this compound. Elementary analysis and X-ray crystal structures are in accordance with earlier results on the ease of solvent loss and theoretical studies dealing with acetonitrile–exchange reactions.

Theoretical study of acetonitrile‐exchange reactions on hexasolvated divalent cations in the first transition series elements

AbstractPenta‐, hexa‐, and heptaacetonitrile complexes of divalent cations of the first transition series are studied by ab initio molecular orbital calculations. The factors that determine the structural stability and the reaction mechanism of solvent‐exchange reactions are discussed. All the penta‐ and hexaacetonitrile species are at local minima, whereas the geometrical stability of the heptacoordinated species depends on the 3d electron configurations. The structural stability of heptaacetonitrile species is intermediate between those of hydrogen cyanide complexes and hydrates. Acetonitrile exchange reactions have more dissociative character than hydrogen cyanide exchange reactions because the inductive effect of the methyl group in CH3CN destabilizes the heptacoordinated structures. The successive binding energies show that associative mechanisms are favorable for acetonitrile exchange with earlier members of the first transition series, whereas dissociative mechanisms become favorable for later members. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009

Homogeneous Decomposition of Aryl- and Alkylimido Precursors for the Chemical Vapor Deposition of Tungsten Nitride: A Combined Density Functional Theory and Experimental Study

MOCVD growth of tungsten nitride (WN(x)()) and tungsten carbonitride (WN(x)()C(y)()) thin films has been reported from the complexes Cl(4)(CH(3)CN)W(NR) (1: R = Ph; 2: R = (i)Pr; 3: R = C(3)H(5)). To evaluate the role of the imido substituent in film growth, gas-phase homogeneous decomposition of precursor molecules was investigated using density functional theory (DFT) calculations. Computational results and NMR kinetics of acetonitrile exchange by 2 in solution verified that dissociation of the acetonitrile ligand should be facile for 1-3 in the temperature range used for film growth (>450 degrees C). A computational search for transition states for cleavage of W-Cl bonds in the presence of H(2) carrier gas was consistent with a sigma-bond metathesis pathway. Natural bonding orbital (NBO) analysis and bond energy calculations indicated that 1 has a stronger N-C(imido) bond and a slightly weaker W-N bond than 2 and 3, suggesting a greater role for W-N bond cleavage in depositions from 1. These results are consistent with mass spectrometric fragmentation patterns from 1-3 and low nitrogen content in films deposited from 1 as compared to those from 2 and 3.

Direct Determination of the Anisotropy and Exchange Splittings in the Dimeric Single-Molecule Magnet [Mn4O3Cl4(O2CEt)3(py)3]2·8MeCN by Inelastic Neutron Scattering

Energy splittings resulting from anisotropy and exchange interactions in the dimer of single-molecule magnets [Mn4O3Cl4(O2CEt)3(py)3]2.8MeCN are determined for both an undeuterated and a partially deuterated sample using inelastic neutron scattering. The antiferromagnetic (AF) exchange coupling between the two Mn4 subunits strongly depends on their separation. The Cl...Cl distance between the two subunits can be modified either by exchanging the solvent of crystallization or by deuteration of the C-H...Cl hydrogen bonds. The exchange of acetonitrile for n-hexane leads to a five times greater shortening of the Cl...Cl separation than does full deuteration of all the hydrogen bonds. As a result, the AF exchange coupling constants between the subunits are 0.0073(4) and 0.0103(9) meV in the samples with acetonitrile and n-hexane solvent molecules, respectively, in the crystal structure. On the other hand, the effect of C-H...Cl deuteration on the AF exchange coupling is not detectable within the experimental accuracy of INS.

Preparation of poly(methyl methacrylate) films containing silica particle array structure from colloidal crystals

The incorporation of monodisperse, polymer-modified silica into poly(methyl metharylate) to prepare polymer films containing particle array structure was investigated. The preparation was carried out by a two-step radical polymerization for gelation and solidification. The colloidal crystallization of poly(methyl metharylate)-modified silica, in 78 nm size, in acetonitrile and successive copolymerization of methyl methacrylate and 1,2-dimethacryloylethane by UV light irradiation gave the polymer gel containing the colloidal crystal structure. The exchange of acetonitrile in the gel with methyl methacrylate and further photo-radical polymerization gave the durable polymer film composed of silica particle array.

Cooperative bimetallic reactivity: hydrogen activation in two-electron mixed-valence compounds.

Reversible dihydrogen uptake by a two-electron mixed-valence di-iridium complex is examined with nonlocal density-functional calculations. Optimized metrics compare favorably with crystal structures of isolated species, and the calculated activation enthalpy of acetonitrile exchange is accurate within experimental error. Dihydrogen attacks the Ir(2) core at Ir(II); the Ir(0) center is electronically saturated and of incorrect orbital parity to interact with H(2). Isomeric eta(2)-H(2) complexes have been located, and harmonic frequency calculations confirm these to be potential energy minima. A transition state links one such complex with the final dihydride; calculated atomic charges suggest a heterolytic H(2) bond scission within the di-iridium coordination sphere. This investigation also establishes a ligand-design criterion for attaining cooperative bimetallic reactivity, namely, that the supporting ligand framework has sufficient mechanical flexibility so that the target complex can accommodate the nuclear reorganizations that accompany substrate activation.

Calix[6]arene-based cuprous "funnel complexes": a mimic for the substrate access channel to metalloenzyme active sites.

Two calixarene-based model systems (a and b) for monocopper enzymes are compared. Both present a tris(pyridine) coordination site for Cu that mimics the imidazole-rich neutral binding site in enzymes. Upon reaction with 1 equiv of copper(I), the tridentate ligands gave rise to ill-defined unsymmetrical complexes. However, in the presence of an organonitrile RCN (R = Me, Et, Ph), tetrahedral species were obtained, with the nitrilo ligand included in the calixarene hydrophobic cone. System b presents a larger cavity than system a, with a wider opening thanks to the removal of three tBu groups from the calixarene structure. As a result, the recognition pattern for MeCN vs PhCN is inverted, and the relative affinity constants differ by 3 orders of magnitude. The mechanism of the acetonitrile exchange at the cuprous centers was studied by (1)H NMR spectroscopy. Thermodynamic and kinetic data show that it follows a dissociative pathway in both cases. The main differences between systems a and b stem from the presence of a door that entraps the guest in case a. In system b indeed, the removal of three calixarene tBu groups led to a 100-fold acceleration of the MeCN exchange rate. Hence, these supramolecular systems provide a rare and interesting model for the hydrophobic substrate channel giving access to a metalloenzyme active site.

C [bond] H activation by cationic platinum(II) complexes: ligand electronic and steric effects.

A series of bis(aryl)diimine-ligated methyl complexes of Pt(II) with various substituted aryl groups has been prepared. The cationic complexes [(ArN=CR [bond] CR=NAr)PtMe(L)](+)[BF(4)](-) (Ar = aryl; R = H, CH(3); L = water, trifluoroethanol) react smoothly with benzene at approximately room temperature in trifluoroethanol solvent to yield methane and the corresponding phenyl Pt(II) cations, via Pt(IV)-methyl-phenyl-hydrido intermediates. The reaction products of methyl-substituted benzenes suggest an inherent reactivity preference for aromatic over benzylic C [bond] H activation, which can however be overridden by steric effects. For the reaction of benzene with cationic Pt(II) complexes bearing 3,5-disubstituted aryl diimine ligands, the rate-determining step is C [bond] H activation, whereas for the more sterically crowded analogues with 2,6-dimethyl-substituted aryl groups, benzene coordination becomes rate-determining. This switch is manifested in distinctly different isotope scrambling and kinetic deuterium isotope effect patterns. The more electron-rich the ligand is, as assayed by the CO stretching frequency of the corresponding carbonyl cationic complex, the faster the rate of C [bond] H activation. Although at first sight this trend appears to be at odds with the common description of this class of reaction as electrophilic, the fact that the same trend is observed for the two different series of complexes, which have different rate-determining steps, suggests that this finding does not reflect the actual C [bond] H activation process, but rather reflects only the relative ease of benzene displacing a ligand to initiate the reaction; that is, the change in rates is mostly due to a ground-state effect. The stability of the aquo complex ground state in equilibrium with the solvento complex increases as the diimine ligand is made more electron-withdrawing. Several lines of evidence, including the mechanism of degenerate acetonitrile exchange for the methyl-acetonitrile Pt(II) cations in alcohol solvents, suggest that associative substitution pathways operate to get the hydrocarbon substrate into, and out of, the coordination sphere; that is, the mechanism of benzene substitution proceeds by a solvent (TFE)-assisted associative pathway.

A 1H NMR study of the kinetics of the acetonitrile exchange in the complex decakis(acetonitrile)dirhenium(II,II)

The pseudo-first-order rate constant, k, for the substitution of the eight equatorial acetonitrile ligands in the complex [Re 2(NCCH 3) 10] 4+ with acetonitrile has been determined by 1H NMR in CD 3CN solution in the temperature range 298–333 K. The results obtained were: k=(8.3±0.5)×10 −7 s −1 (half-life: 9.6±0.5 days) at 298.0 K, Δ H ‡=109±2 kJ mol −1 and Δ S ‡=6±6 J mol −1 K −1. The exchange of the two axially coordinated acetonitrile ligands was found to be fast on the NMR time-scale.

H/D Exchange of Amines and Acetonitrile over Transition Metal Catalysts

H/D exchange of acetonitrile, mono-, di-, and triethylamine was carried out at 75 °C over zeolite supported transition metal catalysts in a fixed-bed microflow reactor. In order to identify the location of the D atoms, the product of this primary exchange was, subsequently, subjected to secondary exchange with liquid D2O, which affects exclusively the N-bonded hydrons. 1H-NMR and mass spectrometry were used for product analysis. The results reveal a rather dramatic difference in exchange behavior between ruthenium and the group of metals including Pt, Pd, and Ni, while Rh displays an intermediate behavior. Pt, Pd, and Ni show stepwise exchange starting with the N-bonded hydrons. In contrast, multiple exchange is found for Ru; this exchange leads to preferential formation of d3 acetonitrile. With primary, secondary, and tertiary amines, the hydrons bonded to the methylene C atom are most rapidly exchanged over Ru, followed by the hydrons in methyl groups. Surprisingly, the N-bonded hydrons are only negligi...

Crystal Structures and Acetonitrile Exchange of Palladium(II) Complexes with Bis(3-aminopropyl)amine and Diethylenetriamine. Effects of Ion-Pair Formation

Abstract The crystal structures of palladium(II) complexes with tridentate amine and acetonitrile, [Pd(CH3CN)(dptn)](CF3SO3)2 (1) and [Pd(CH3CN)(dien)](CF3SO3)2 (2) (dptn = bis(3-aminopropyl)amine and dien = diethylenetriamine), have been determined by X-ray crystal structure analysis. The central palladium(II) ion has a distorted square-planar geometry. The five-membered chelate rings of the dien ligand in 2 are more strained than the six-membered chelate rings of the dptn ligand in 1, as indicated from the difference in the angles of terminal N–Pd–terminal N and the averaged Pd–N–C angles around the terminal nitrogens. The kinetics of acetonitrile exchange of 1, 2, and [Pd(CH3CN)(dien)](BF4)2 (3) have been investigated by the 1H NMR line-broadening technique. The observed rate constants can be expressed by kobs = k1 + k2 [CH3CN] from the dependence of kobs on the acetonitrile concentration. It has been indicated that the k1 and k2 paths proceed via the dissociative and associative modes of activation, respectively. The dissociative k1 path is promoted by the ion-pair formation where the bound ligand effect is enhanced by the electrostatic interaction between the counter anions and amine protons. The reaction mechanisms are discussed in terms of the steric and electronic factors of the bound ligands (dptn and dien) and the effect of the ion-pair formation with the counter anions (CF3SO3− and BF4−).

Dissociative Path Promoted by Ion Pair Formation for Acetonitrile Exchange Reaction of the Palladium(II) Complex with Diethylenetriamine

Abstract The acetonitrile exchange rates at the palladium(II) complex with diethylenetriamine have been measured at various temperatures by the NMR line-broadening method. The dependence of the exchange rate on the concentration of the free solvent indicates the two reaction paths with dissociative and associative mechanisms. This unique concerted mechanism has been ascribed to the promotion of the dissociative path by the ion pair formation with tetrafluoroborate.

High-pressure proton NMR study of acetonitrile exchange kinetics on [Rh 2(CH 3CN) 10] 4+ and 17O NMR investigation of aqueous solutions of [Rh 2(H 2O) 10] 4 +

The 1H NMR spectrum of [Rh 2(e-CH 3CN) 8(a-CH 3CN) 2](BF 4) 4 supports the presence in solution of this dinuclear species with a 4/1 equatorial/axial ratio. The lability of the axial acetonitrile is high on the NMR time scale, suggesting a dissociative mechanism of exchange with bulk acetonitrile. In contrast the equatorial acetonitrile exchange rate is slow and has been followed by 1H NMR isotopic labelling: k 298=3.1×10 −5 s −1, δ H‡=65.6 kJ mol −1, δ S‡=−111.0 J K −1 mol −1, and δ V=−4.9 cm 3 mol −1. It is suggested that a concerted migration of the a-CH 3CN molecule to the equatorial plane and release of an e-CH 3CN molecule to the bulk takes place through a contracted transition state. The 17O NMR spectrum of the dinuclear Rh(II) aqua-ion is consistent with the entity [Rh 2(e-H 2O) 8(a-H 2O) 2] 4+. This aqua-ion is not very stable and decomposes, within 1 h at 339 K, forming metallic Rh and [Rh(H 2O) 6] 3+. The equatorial water exchange rate constant is estimated to be 10< k 298 <50 s −1, whereas the axial water exchange rate is larger than 10 4 s −1 at 298 K. It is believed that the water exchange mechanisms for the dinuclear Rh(II) aqua-ion are similar to those suggested for the acetonitrile analogue.

Investigation of alkali metal-water interactions in acetonitrile

The exchange of acetonitrile into and out of the coordination sphere of alkali metal ions is fast on the NMR time scale and slow on the vibrational time scale. This results in separate infrared and Raman spectra for coordinated and non-coordinated solvents in solutions of alkali metal salts in acetonitrile. The 1H NMR spectra, on the other hand, are averages of coordinated and non-coordinated environoments. Addition of water to solutions of alkali metal salts in acetonitrile indicates that the cation is again preferentially solvated by water. The water completely replaces acetonitrile in the lithium coordination sphere until four waters have been added. Water also displaces the first acetonitrile from the coordination sphere of sodium and potassium ions. However, when additional water is added there is an equilibrium mixture of various species. Spectroscopic study of these solutions allows one to gain insights about the energetics and geometry of the cation. Experimental results from NMR, Raman and IR measurements along with extended Hückel molecular orbital calculations are used to discuss the alkali metal cation- water-acetonitrile system.

Acetonitrile exchange reactions of [WI 2(CO)(NCMe)(η 2-RC 2R) 2] (R = Me or Ph) and [WI(CO)(NCMe){(Ph 2PCH 2)PPh 2}(η 2-MeC 2Me)[BF 4] with thiophene-3-acetonitrile. X-ray crystal structure of [WI 2(CO){(NCCH 23-C 4H 3S)}(η 2-MeC 2Me) 2

The complexes [WI 2(CO)(NCMe)(η 2-RC 2R) 2] (R = Me or Ph) and [WI(CO)(NCMe)(Ph 2P(CH 2)PPh 2)(η 2-MeC 2Me)][BF 4] react with equimolar quantities of thiophene-3-acetonitrile (NCCH 2(3-C 4H 3S)) in dichloromethane at room temperature to give the acetonitrile-exchanged products [WI 2(CO){(NCCH 23-C 4H 3S)}(η 2-RC 2R) 2] ( 1 and 2) and [WI(CO){(NCCH 23-C 4H 3S)}{(Ph 2PCH 2)PPh 2}(η 2-MeC 2Me)][BF 4] ( 3) respectively in good yields. The crystal structure of [WI 2(CO){(NCCH 2(3-C 4H 3S)}(η 2-MeC 2Me) 2] ( 1) was determined. The coordination geometry about the tungsten may be regarded as octahedral, with the but-2-yne ligands parallel to each other and trans to the iodide ligands. The carbon monoxide and thiophene-3-acetonitrile ligands are mutually trans to each other. 13C NMR spectroscopy indicates that the alkyne ligands in 1 are donating a total of six electrons to the tungsten, whereas the but-2-yne ligand in 3 is donating four electrons to the tungsten. The barrier to but-2-yne rotation of 3 was calculated to be 51.3 kJ mol −1.

Structure and reactivity of ruthenium half-sandwich compounds: crystal and molecular structure and acetonitrile exchange kinetics and mechanism of tris(acetonitrile)(.eta.6-benzene)ruthenium(2+) and tris(acetonitrile)(.eta.5-cyclopentadienyl)ruthenium(+)

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStructure and reactivity of ruthenium half-sandwich compounds: crystal and molecular structure and acetonitrile exchange kinetics and mechanism of tris(acetonitrile)(.eta.6-benzene)ruthenium(2+) and tris(acetonitrile)(.eta.5-cyclopentadienyl)ruthenium(+)Werner Luginbuehl, Pascal Zbinden, Pierre A. Pittet, Thomas Armbruster, Hans Beat Buergi, Andre E. Merbach, and Andreas LudiCite this: Inorg. Chem. 1991, 30, 10, 2350–2355Publication Date (Print):May 1, 1991Publication History Published online1 May 2002Published inissue 1 May 1991https://doi.org/10.1021/ic00010a024RIGHTS & PERMISSIONSArticle Views467Altmetric-Citations86LEARN 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 (659 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

ChemInform Abstract: Variable‐Temperature and ‐Pressure Proton Nuclear Magnetic Resonance Studies of the Rates and Mechanisms of N,N‐Dimethylformamide and Acetonitrile Exchange with the Square‐Pyramidal Complexes Mono(solvent)(3,7,11‐tribenzyl‐3,7,11,17‐tetraazabicyclo(11.3.1)heptadeca‐1(17),13,15‐triene)nickel(II)

ChemInformVolume 20, Issue 36 Organoelement Compounds ChemInform Abstract: Variable-Temperature and -Pressure Proton Nuclear Magnetic Resonance Studies of the Rates and Mechanisms of N,N-Dimethylformamide and Acetonitrile Exchange with the Square-Pyramidal Complexes Mono(solvent)(3,7,11-tribenzyl-3,7,11,17-tetraazabicyclo(11.3.1)heptadeca-1(17),13,15-triene)nickel(II) L. FIELDING, L. FIELDING Dep. Chem., Univ. Warwick, Coventry CV4 7AL, UKSearch for more papers by this authorP. MOORE, P. MOORE Dep. Chem., Univ. Warwick, Coventry CV4 7AL, UKSearch for more papers by this author L. FIELDING, L. FIELDING Dep. Chem., Univ. Warwick, Coventry CV4 7AL, UKSearch for more papers by this authorP. MOORE, P. MOORE Dep. Chem., Univ. Warwick, Coventry CV4 7AL, UKSearch for more papers by this author First published: September 5, 1989 https://doi.org/10.1002/chin.198936307Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume20, Issue36September 5, 1989 RelatedInformation

Investigation of lithium-water interactions in acetonitrile solutions using proton nuclear magnetic resonance, Raman, and infrared spectroscopies and extended Hueckel molecular orbital calculations

Exchange of acetonitrile into and out of the coordination sphere of lithium ion is shown to be fast on the NMR time scale and slow on the vibrational time scale. Addition of water to solutions of lithium perchlorate in acetonitrile indicates that lithium is preferentially solvated by water and reveals that the solvation number of lithium ion is 4. Results from NMR, IR, Raman, and extended Huckel molecular orbital calculations are used to discuss the LiClO 4 -H 2 O-CH 3 CN system

Variable-temperature and -pressure proton nuclear magnetic resonance studies of the rates and mechanisms of N,N-dimethylformamide and acetonitrile exchange with the square-pyramidal complexes mono(solvento){3,7,11-tribenzyl-3,7,11,17-tetra-azabicyclo [11.3.1]heptadeca-1(17),13,15-triene}nickel(II)

Rates and activation parameters have been determined for solvent (solv) exchange with square-pyramidal complexes [Ni(L1)(solv)]2+[L1 is the pyridine-containing tetra-aza macrocycle, 3,7,11-tribenzyl-3,7,11,17-tetra-azabicyclo[11.3.1]heptadeca-1 (17),13,15-triene; solv =N,N-dimethylformamide or acetonitrile] using variable-temperature and -pressure 1H n.m.r. spectroscopy. At 298.2 K 10–2kex/s–1= 32.7 ± 1.9 and 3.82 ± 0.29, ΔH‡sol;kJ mol–1= 36.3 ± 1.1 and 68.9 ± 3.8, ΔS‡/J K–1 mol–1=–55.8 ± 3.3 and +35.6 ± l2.3, and at 323 K, ΔV‡/cm3mol–1=+10.6 ± 0.8 and –3.5 ± 0.9 for solv =N,N-dimethylformamide and acetonitrile respectively. The mechanistic significance of these data is discussed.