Strong Solvent Dependence Research Articles

Photophysics of 1,8-Bis(dimethylamino)naphthalene in Solution: Internal Charge Transfer with a Twist

The photophysical properties of the excited states of 1,8-(bisdimethylamino)naphthalene have been investigated by a combination of experimental spectroscopic methods and quantum chemical calculations. The experiments show that vertical excitation occurs to an 1La-type state from which internal conversion occurs to a state with dominant internal charge-transfer character. This character gives rise to weak emissive properties, a strong solvent dependence of the emission, and transient absorption spectra that carry the signature of the steady-state absorption spectra of the naphthalene radical anion. The quantum chemical calculations support the interpretation of the experimental studies, and enable us to put their results into a broader perspective. They explain the order of the lower excited states of 1,8-(bisdimethylamino)naphthalene and related compounds as well as the role of intramolecular relaxation upon excitation, thereby elucidating the large Stokes shift already observed in nonpolar solvents.

Exciplex formation of copper(II) octaethylporphyrin revealed by pulsed X-rays

Abstract The triplet excited structures of Cu(II) octaethylporphyrin (CuOEP) in toluene and in 1:1 mixture of toluene and tetrahydrofuran (THF) were investigated by time-domain laser pulse pump, X-ray pulse probe X-ray absorption spectroscopy (pump–probe XAS) at room temperature using X-rays from a third generation synchrotron source with 100-ps time resolution. The transient optical absorption measurements indicate a strong solvent dependency of the triplet excited state lifetime due to the presence of oxygen-containing solvent molecules. While the ground state CuOEP molecules remain square-planar in both solvents, the attenuation of a peak attributed to the 1s → 4p z transition at the Cu K-edge for the laser excited CuOEP in the THF/toluene mixture revealed the penta-coordinated exciplex formation which is responsible for the shortening of the triplet excited state lifetime. Meanwhile, the average Cu–N distance in the triplet excited state is lengthened by 0.03 A due to ligation with a THF solvent molecule, which agrees with a domed coordination structure for copper in the penta-coordinated exciplex.

Experimental studies of the 13C NMR of iodoalkynes in Lewis-basic solvents.

The (13)C NMR spectra of two different iodoalkynes, 1-iodo-1-hexyne (1) and diiodoethyne (2), exhibit a strong solvent dependence. Comparisons of the data with several common empirical models, including Gutmann's Donor numbers, Reichardt's E(N)(T), and Taft and Kamlet's beta and pi, demonstrate that this solvent effect arises from a specific acid-base interaction. Solvent basicity measures such as Donor numbers and beta values correlate well with the alpha-carbon chemical shift of 1, but polarity measures such as E(N)(T) and pi do not correlate. The similarity of the solvent effect for 1 and 2 suggests that carbon-carbon bond polarization may not play a role in the change in chemical shift, as previously hypothesized.

Nuclear magnetic resonance and optosensing properties of di-2-thienyl ketone p-nitrophenylhydrazone (DSKNPH) in non-aqueous media

The compound di-2-thienyl ketone p-nitrophenylhydrazone (DSKNPH) melting point 168–170 °C was isolated in good yield from the reaction between di-2-thienyl ketone (DSK) and p-nitrophenylhydrazine in refluxing ethanol containing a few drop of concentrated HCl. Nuclear magnetic resonance studies on DSKNPH in non-aqueous solvents revealed strong solvent and temperature dependence due to solvent–solute interactions. Optical measurements on DSKNPH in DMSO in the presence and absence of KPF 6 gave extinction coefficients of 83,300±2000 and 25,600±2000 M −1 cm −1 at 612 and 427 nm at 295 K. In CH 2Cl 2, extinction coefficient of 34,000±2000 M −1 cm −1 was calculated at 422 nm. When DMSO solutions of DSKNPH were allowed to interact with DMSO solutions of NaBH 4 the low energy electronic state becomes favorable and when DMSO solutions of DSPKNPH where allowed to interact with DMSO solutions of KPF 6 or NaBF 4, the high energy electronic state becomes favorable. The reversible BH 4 −/BF 4 − interconversion points to physical interactions between these species and DSKNPH and hints to the possible use of DSKNPH as a spectrophotometric sensor for a variety of physical and chemical stimuli. Thermo-optical measurements on DSKNPH in DMSO confirmed the reversible interconversion between the high and low energy electronic states of DSKNPH and allowed for the calculations of the thermodynamic activation parameters of DSKNPH. Changes in enthalpy (Δ H ∅) of +57.67±4.20; 27.15±0.90 kJ mol −1, entropy (Δ S ∅) of +160±12.88; 83±2.91 J mol −1 and free energy (Δ G ∅) of −8.52±0.40; 2.66±0.25 kJ mol −1 were calculated at 295 K in the absence and presence of NaBH 4, respectively. Manipulation of the equilibrium distribution of the high and low energy electronic states of DSKNPH allowed for the use of these systems (DSKNPH and surrounding solvent molecules) as molecular sensors for group I and II metal ions. Group I and II metal ions in concentrations as low as 1.00×10 −5 M can be detected and determined using DSKNPH in DMSO.

Structural, electrochemical and optical properties of di-2-pyridyl ketone 2-furoic acid hydrazone (dpkfah)

Crystals of di-2-pyridyl ketone 2-furoic acid hydrazone (dpkfah), obtained from a dmso (dimethylsulfoxide) solution of dpkfah, are in the monoclinic space group, P2 1/ n. Structural analysis reveals planar hydrazone moiety, non-coplanar pyridine rings and infinite chains of anti-parallel dpkfah dimers interlocked via a web of hydrogen bonds. Electrochemical measurements on dpkfah in non-aqueous solvents show solvent dependence, single and multi-electronic transfers and electrochemical transformation(s) following the first oxidative or reductive electronic transfer. Optical measurements on dpkfah in non-aqueous solvents show strong solvent dependence. In non-polar solvent such as CH 2Cl 2 a single electronic absorption band with extinction coefficient of 18,600±2000 M −1 cm −1 appeared at 325 nm and in polar solvents a low-energy absorption band at ∼396 nm and a high-energy absorption band at ∼320–335 nm appeared that are concentration, temperature and salt dependent. In the presence and absence of NaBF 4 and NaBH 4, extinction coefficients of 21,000±2000 and 22,500 M −1 cm −1, and 17,200±2,000 and 23,000 M −1 cm −1 were calculated for the low and high energy electronic states of dpkfah in dmf and dmso, respectively at 295 K. Thermo-optical measurements on dpkfah in dmso and dmf confirmed the reversible interconversion between the high and low energy electronic states of dpkfah and allowed calculations of their thermodynamic activation parameters and gave changes in enthalpy (Δ H ∅) of +47.5±1.2 and −16.3±0.4 kJ mol −1, entropy (Δ S ∅) of +147.7±3.8 and −64.4±1.64 J mol −1 K −1 and free energy (Δ G ∅) of +3.49±0.2 and +2.85±0.2 kJ mol −1 and hence equilibrium constant ( K) of +0.25±0.05 and +0.32±0.05 in dmso and dmf, respectively. The reversible BH 4 −/BF 4 − interconversion of the electronic states of dpkfah points to weak non-covalent interactions between these species and dpkfah and possible use of dpkfah as a spectrophotometric sensor for a variety of physical and chemical stimuli. Chemical stimuli in concentrations <1.00×10 −6 M can be detected and determined using dpkfah in non-aqueous media.

Photochemical nitric oxide precursors: synthesis, photochemistry, and ligand substitution kinetics of ruthenium salen nitrosyl and ruthenium salophen nitrosyl complexes.

Described are syntheses, characterizations, and photochemical reactions of the nitrosyl complexes Ru(salen)(ONO)(NO) (I, salen = N,N'-ethylenebis(salicylideneiminato) dianion), Ru(salen)(Cl)(NO) (II), Ru((t)Bu(4)salen)(Cl)(NO) (III,(t)Bu(4)salen = N,N'-ethylenebis(3,5-di-tert-butylsalicylideneiminato) dianion), Ru((t)Bu(4)salen)(ONO)(NO) (IV), Ru((t)Bu(2)salophen)(Cl)(NO) (V, (t)Bu(2)salophen = N,N'-1,2-phenylenediaminebis(3-tert-butylsalicylideneiminato) dianion), and Ru((t)Bu(4)salophen)(Cl)(NO) (VI, (t)Bu(4)salophen = N,N'-1,2-phenylenebis(3,5-di-tert-butylsalicylideneiminato) dianion). Upon photolysis, these Ru(L)(X)(NO) compounds undergo NO dissociation to give the ruthenium(III) solvento products Ru(L)(X)(Sol). Quantum yields for 365 nm irradiation in acetonitrile solution fall in a fairly narrow range (0.055-0.13) but decreased at longer lambda(irr). The quantum yield (lambda(irr) = 365 nm) for NO release from the water soluble complex [Ru(salen)(H(2)O)(NO)]Cl (VII) was 0.005 in water. Kinetics of thermal back-reactions to re-form the nitrosyl complexes demonstrated strong solvent dependence with second-order rate constants k(NO) varying from 5 x 10(-4) M(-1) s(-1) for the re-formation of II in acetonitrile to 5 x 10(8) M(-1) s(-1) for re-formation of III in cyclohexane. Pressure and temperature effects on the back-reaction rates were also examined. These results are relevant to possible applications of photochemistry for nitric oxide delivery to biological targets, to the mechanisms by which NO reacts with metal centers to form metal-nitrosyl bonds, and to the role of photochemistry in activating similar compounds as catalysts for several organic transformations. Also described are the X-ray crystal structures of I and V.

Optical, electrochemical and structural studies on the first rhenium compound of di-2-pyridylketonephenylhydrazone (dpkphh), fac-Re(CO) 3(dpkphh)Cl

fac-Re(CO) 3(dpkphh)Cl isolated from the reaction between Re(CO) 5Cl and dpkphh in refluxing toluene exhibits rich physico-chemical properties. Spectroscopic measurements on fac-Re(CO) 3(dpkphh)Cl revealed strong solvent dependence as manifested by the high sensitivity of its 1H NMR and electronic absorption spectra to solvent variation. Electrochemical measurements on fac-Re(CO) 3(dpkphh)Cl in CH 2Cl 2 show irreversible/quasi-reversible redox processes pointing to electrochemical transformation(s) following electronic-transfer(s). Crystals of fac-Re(CO) 3(dpkphh)Cl·CH 3CN obtained from an acetonitrile solution of fac-Re(CO) 3(dpkphh)Cl are chiral and structural studies show racemic twins of fac-Re(CO) 3(dpkphh)Cl.CH 3CN with fac-Re(CO) 3(dpkphh)Cl molecules in distorted octahedral geometry. The molecules pack shows stacks of well separated strands of fac-Re(CO) 3(dpkphh)Cl·CH 3CN in double helix formation with a network of hydrogen bonds that include solvent–solute and solute–solute interactions. The interlocked helical structure of fac-Re(CO) 3(dpkphh)Cl·CH 3CN and weak bond energies of the non-covalent interactions may account for the optical behavior of fac-Re(CO) 3(dpkphh)Cl·CH 3CN as any slight interaction between this system ( fac-Re(CO) 3(dpkphh)Cl and surrounding solvent molecules) and its surroundings may disrupt the weak solvent–solute and solute–solute interactions.

Synthesis, Characterization and Structural Studies on the First Rhenium Complex with Di(2-pyridyl) Ketone 2,4-Dinitrophenylhydrazone (dpkdnph),fac-[Re(CO)3(dpkdnph)Cl

When di(2-pyridyl) ketone 2,4-dinitrophenylhydrazone (dpkdnph) was allowed to react with [Re(CO)5Cl] in refluxing toluene fac-[Re(CO)3(dpkdnph)Cl] was formed in good yield. Spectroscopic measurements on fac-[Re(CO)3(dpkdnph)Cl] revealed strong solvent dependence as manifested by the high sensitivity of its electronic absorption spectra to solvent variation. Electrochemical measurements on fac-[Re(CO)3(dpkdnph)Cl] in DMF show electrochemical properties with quasi-reversible reductions following an irreversible one-electron transfer. Structural studies on a brown crystal of fac-[Re(CO)3(dpkdnph)Cl]·CH3CN grown from an acetonitrile solution of fac-[Re(CO)3(dpkdnph)Cl] show well separated linear CH3CN and pseudo-octahedral fac[Re(CO)3(dpkdnph)Cl], with the major distortion about rhenium being due to the bidentate binding of dpkdnph to form a six-membered Re−N−C−C−C−N metallacyclic ring in a boat conformation. The molecular packing shows a web of fac-[Re(CO)3(dpkdnph)Cl]·CH3CN units interlocked via a network of intra- and intermolecular non-covalent interactions that include donor/acceptor and hydrogen bonds.

Unusual phenomena during the resolution of 6-fluoro-2-methyl-1,2,3,4-tetrahydroquinoline (FTHQ): thermodynamic-kinetic control

6-Fluoro-2-methyl-1,2,3,4-tetrahydroquinoline (FTHQ) was resolved in several different solvents by tartaric acid derivatives as the most common acidic resolving agents available in industrial quantities. Strong reaction kinetics and solvent dependence were observed, curiously without solvation. In possession of these findings, an economic resolution process is proposed, which is completed by the incorporation of a racemization step.

Synthesis, Structural Characterization, Solvatochromism, and Electrochemistry of Tetra-Osmium Carbonyl Clusters Containing Azo-Ligands

The reaction of [Os4(μ-H)4(CO)12] with 4-(2-pyridylazo)-N,N-dimethylaniline (PNNDA) in dichloromethane afforded the new clusters [Os4(μ-H)4(CO)11{NC5H4(N=N)C6H4NMe2}] (1) and [Os4(μ-H)4(CO)10{η2-NC5H4(N=N)C6H4NMe2}] (2) in 34% and 15% yields, respectively. Upon heating in toluene under reflux, compound 1 converted into 2 in 80% yield. The MLCT transition of compound 2 shows strong solvent dependency, displaying unusually large positive solvatochromism in different organic solvents. Treatment of [Os4(μ-H)4(CO)12] with 2-(5-bromo-2-pyridylazo)-5-(diethylamino)phenol (Br-PADAP) in dichloromethane gives [Os4(μ-H)3(CO)10{μ-η3-Et2NC6H3(O)(N=N)C5NH3Br}] (3). The O−H bond activation is observed and the azo-ligand behaves as a five-electron donor. The clusters [Os4(μ-H)2(CO)10{μ-η3-NC5H4(N=N)C5H4N}] (4) and [Os4(μ-H)4(CO)10{μ-η2-NC5H4(N=N)C5H4N}]2 (5) were isolated from the reaction of [Os4(μ-H)4(CO)10(NCMe)2] with 2,2′-azopyridine and 3,3′-azopyridine, respectively. In compound 4, both pyridine and azo nitrogen atoms were found to coordinate to the cluster core. Dehydrogenation was also observed in this compound. For compound 5, two tetra-osmium metal cores were connected by two azo ligands through their pyridyl nitrogen atoms to form a novel cyclic structure. The redox properties of the compounds described herein were investigated by means of cyclic voltammetry and controlled potential coulometry. Both compound 2 and 5 exhibit a reversible cathodic wave, which indicates that they undergo addition of one electron without significant structural changes. Furthermore, compound 5 displays an electronic interaction between two redox centers, the extra electrons are believed to delocalize throughout the cyclic structure.

Stereochemistry and Pseudosymmetries in Main Chain Polymeric Free Radicals

Main chain free radicals produced from 248 nm photolysis of poly(alkyl acrylate)s and poly(alkyl methacrylate)s have been unambiguously characterized for the first time by time-resolved electron paramagnetic resonance (TREPR) spectroscopy. Side chain cleavage via the Norrish I process dominates, leading to an oxo-acyl radical from the ester side chain and a main chain polymeric radical, the existence of which has been previously postulated but never confirmed by direct spectroscopic observation. There is a strong stereochemical influence on the methacrylate spectra, which manifests itself through changes in the TREPR spectra as a function of polymer tacticity and temperature. There is also a strong solvent dependence. Computer simulation provides unambiguous assignment of the signal carriers for the acrylate polymers at room temperature and above, and for PMMA main chain radicals at high temperature, where the fast motion limit for the β-methylene hyperfine coupling constants is achieved. The methacrylate spectra give remarkably similar coupling constants for all tacticities at high temperature, a phenomenon explained by an unexpected (and fortuitous) pseudosymmetry relationship between the diastereotopic protons in the radicals.

EPR properties of two new cyclic phosphinylhydrazyl radicals and of their inclusion complexes with cyclodextrins

Two phosphorus-containing hydrazines, namely morpholin-4-ylphosphoramidic acid diethyl ester (1a) and (2,2,6,6-tetramethylpiperidin-1-yl)phosphoramidic acid diethyl ester (2a), have been synthesized. The corresponding hydrazyl radicals (1b and 2b) have been obtained, by in situ oxidation, and their properties have been investigated by EPR spectroscopy. The 1b radical shows spectra strongly dependent on temperature due to the inversion of the morpholin ring and to rotation about the N-N bond. Since, in the investigated temperature range, both motions take place in the EPR time scale, a kinetic study of these process could be made by analyzing the spectral line-shape variations. The 2b radical is highly persistent and shows a strong temperature and solvent dependence of the phosphorus splitting. The latter property was usefully exploited to study the guest-host interaction of this radical with cyclodextrins. A method is also proposed for the determination of affinity constants for cyclodextrins of nonparamagnetic compounds.

Synthesis, characterization and crystal structures of some tungsten and triosmium carbonyl complexes with monopyridyl and dipyridyl azo ligands

Substitution reactions of [W(CO) 5(THF)] with the azo-functionalized monopyridyl and dipyridyl ligands, namely, 4-phenylazopyridine L 1 and 4,4′-azopyridine L 2 , readily afford two tungsten carbonyl complexes [W(CO) 5(NC 5H 4NNC 6H 5)] ( 1) and [(CO) 5W(μ-NC 5H 4NNC 5H 4N)W(CO) 5] ( 2) in good yields. Ligation of L 1 and L 2 with the activated triosmium carbonyl cluster [Os 3(CO) 10(NCMe) 2] by ortho-metallation reaction provides [Os 3(μ-H)(CO) 10(μ-NC 5H 3NNC 6H 5)] ( 3) and the linking cluster [Os 3(μ-H)(CO) 10(μ-NC 5H 3NNC 5H 3N)Os 3(μ-H)(CO) 10] ( 4) in satisfactory yields. All of the complexes have been fully characterized by IR, 1H-NMR, UV–vis spectroscopies, fast atom bombardment (FAB) mass spectrometry and electrochemical measurements. The solid-state molecular structures of 1– 4 have been ascertained by single-crystal X-ray diffraction methods. The structures of 1 and 3 involve the coordination of L 1 to one {W(CO) 5} and {Os 3(CO) 10} moieties, respectively. In the case of 2 and 4, two identical metal cores are linked together by the bridging ligand L 2 . Spectroscopic investigations revealed that the metal-to-ligand charge transfer (MLCT) transitions of 1 and 2 demonstrate strong solvent dependency, displaying a large negative solvatochromism in a wide range of organic solvents.

Stabilised (H2)Al–E(H)R species, E = P or As, R− = C(SiMe3)2(6-Me-2-pyridyl)−

Reaction of RECl2 (R− = C(SiMe3)2(6-Me-2-pyridyl)−, E = P or As) with LiAlH4 in THF affords directly bonded aluminium hydride–pnictide hydride complexes as weakly associated hydride bridged dimers, [RE(H)–Al(H)2]2; a strong solvent dependency of these reactions, which had previously been observed with the formation of the disecondary diphosphane in Et2O (E = P), is further confirmed by the formation of RAsH2 from RAsCl2 and LiAlH4 in Et2O.

Selective Photoexcitation of the Thione and Thiol Forms of N-Hydroxypyridine-4(1H)-Thione: A Tautomeric Heteroaromatic System

The strong solvent-dependence of the tautomeric equilibrium exhibited by N-hydroxypyridine-4(1H)-thione (4-NHPT) and the distinct absorption properties of the thione and thiol tautomers offer the r...

Photodissociation of I 2 in solution: the observation of solvent-dependent near-infrared emission associated with I( [formula omitted])–solvent interaction

The photolysis of molecular iodine in solution phase has been investigated by Fourier transform techniques coupled with an ultrasensitive near-infrared detecting system. The spectral features and relaxation dynamics of the resulting 1200–1600 nm emission revealed strong solvent dependence. Detailed analyses conclude that the emitting species are attributed to the iodine atom ( 2 P 1/2 → 2 P 3/2 ) magnetic dipole transition in the near infrared perturbed by iodine atom–solvent complexes.

Semiempirical studies of solvent effects on the intramolecular charge transfer of the fluorescence probe PRODAN

The organic chromophore 6-propanoyl-2-(N,N-dimethylamino)naphthalene (PRODAN) is widely used in biochemistry as an efficient fluorescence probe, due to its significant Stokes shift in polar solvents. The nature of the emissive states has not yet been established despite detailed experimental and theoretical investigations. The strong solvent dependence of PRODAN fluorescence requires a quantum mechanical study with explicit consideration of solvent effects. The excited-state properties of PRODAN have been investigated by means of the self-consistent reaction field (SCRF) method in combination with the semiempirical AM1 Hamiltonian. The geometrically unchanged planar conformation and the rotation of the dimethylamino (N) and the propanoyl (O) groups have been explored. Both geometrical relaxation pathways yield a highly polar twisted intramolecular charge-transfer state, the N-TICT and O-TICT states, respectively. These states are energetically stabilised in a polar environment at perpendicular geometries and become the lowest excited state. Based on the calculations, the experimentally observed red-shifted fluorescence is assigned to an emission from the propanoyl TICT state, for which a significantly reduced rotational barrier is found. Agreement with experimental results in various solvents is excellent.

Corrosion of gold by alkane thiols

AbstractSTM images of self assembled alkanethiol films on gold surfaces show holes which have been identified as vacancies in the topmost gold layer. We show that this vacancy formation is accompanied by a corrosion process of gold in ethanolic thiol solutions. The amount of dissolved gold from polycrystalline substrates as a function of immersion time, thiol concentration, chain length and solvent has been investigated by Atomic Absorption Spectroscopy (AAS). The results suggest that the thiol molecule itself is the active oxidant. In case of a 1 mmol solution of docosanethiol in ethanol a gold concentration corresponding to 6% of a gold monolayer has been detected after an immersion time of 24 h. By using hexane as a solvent the amount of dissolved gold is reduced to less than 0.2%, indicating a strong solvent (e.g. polarity) dependence for the corrosion process. The kinetics of the corrosion process have been measured and compared to kinetic data related to the formation of an ordered thiol film.

Solvent Dependence of the First Molecular Hyperpolarizability of p-Nitroaniline Revisited

The solvent effect on the molecular first hyperpolarizability, β, of p-nitroaniline (pNA) has been investigated. Using the hyper-Rayleigh scattering technique, we have also determined β of pNA in DMSO using 1064 nm laser radiation. This β value has not been previously reported. With the help of Onsager's theory, we have arrived at a correction factor to account for the solvent dependence of the values of the intrinsic hyperpolarizability β0. The Onsager model significantly removes the strong solvent dependence of β (or β0) on the dielectric constant.

Mechanism and Solvent Catalysis of the Degenerate 1,12-Metalations of [1.1]Ferrocenophanyllithium and [1.1]Ferrocenophanylsodium Studied by NMR Spectroscopy

Insight into the detailed mechanism of carbon lithiation by an organolithium reagent and of carbon sodiation by an organosodium reagent has been obtained using [1.1]ferrocenophanyllithium (1) and [1.1]ferrocenophanylsodium (3), respectively. In tetrahydrofuran (THF) 1 and 3 undergo rapid 1,12-proton transfer reactions which are coupled with 1,12-lithium ion and 1,12-sodium ion transfers, respectively. It is concluded that the degenerate rearrangement of 1 does not make use of a pseudorotation mechanism, but occurs by direct conversion of a syn-conformer to another syn-conformer. Activation parameters (ΔH⧧ = 19 kJ mol-1 and ΔS⧧ = −93 J K-1 mol-1) for the degenerate reaction of 1 in THF have been measured by dynamic NMR spectroscopy. The primary isotope effect (kH/kD) of the 1,12-hydron transfer is 7.4 ± 1.5 at 320 K. The degenerate rearrangement of 1 shows strong solvent dependence, e.g. the reaction is 4 × 103 times faster in THF than in dimethyltetrahydrofuran (DMTHF). Thus, the rearrangement may be catalyzed by THF in DMTHF. The catalysis is first order in THF at low concentrations of THF. The results show that in the rate-limiting activated complex the lithium ion is coordinating one solvent molecule more than in the initial state. It is paired with a carbanion in which the proton is symmetrically located between the bridge carbons. Compound 3 shows a behavior similar to that of 1, but it is more fluxtional. It also shows a solvent catalysis that is weaker than for 1. It is concluded that 3 also exchanges using an activated complex that contains one solvent molecule more than the initial complex.