14804-25-2Relevant academic research and scientific papers
Ludwig Boltzmann and the Norbornyl Cation
Kramer, G. M.,Scouten, C. G.,Kastrup, R. V.,Ernst, E. R.,Pictroski, C. F.
, p. 6257 - 6260 (1989)
The norbornyl cation is a fluxional species capable of rearranging to as many as 7!*11! degenerate configurations.The process has an associated entropy, depending on how many distinguishable structures are attainable under experimental conditions and this markedly effects the position of hydride-transfer equilibria observable in solution.The equilibration of norbornane with the tert-butyl cation has been observed to be endothermic by 9.6 kcal/mol and be driven toward the formation of the fluxional ion by an entropy change of 34.4 gibbs/mol in the 50-deg span from 193 to 243 K.
Hydride-Transfer Reactions. Temperature Dependence of Rate Constants for i-C3H7++HC(CH3)3=C3H8+C(CH3)3+. Clusters of i-C3H7+ and t-C4H9+ with Propane and Isobutane
Sunner, Jan A.,Hirao, Kimihiko,Kebarle, Paul
, p. 4010 - 4016 (1989)
The rate constant k1 for the hydride-tranfer reaction i-C3H7++i-C4H10=C3H8+t-C4H9+ was measured between 125 and 640 K with a pulsed electron beam high-pressure mass spectrometer.The results for k1 were in good agreement with earlier work of Meot-Ner and Field; however, the transition between the near-collision-limit near-temperature-independent rate constant at low temperature and the negative temperature dependence at high temperature was found to be more gradual.Theoretical calculations of the energy of the reaction complex with the STO-3G basis set, along the reaction coordinate obtained from the MNDO method, indicate that the potential does not have an internal barrier, i.e. is not of the double-well type.This result is consistent with the fact that no stabilised C3H7+*C4H10 complexes were found even at the lowest temperatures used.In mixtures of propane and isobutane, three other adducts were formed: C3H7+*C3H8, C4H9+*C4H10 and C4H9+*C3H8.The third-order rate constants and the ΔH0 and ΔS0 values for the formation of these complexes were determined.A semiempirical treatment of k1 based on the assumption that the back dissociation (kb) of the excited collision complex (C3H7+*C4H10)* can be approximated by that for (C3H7+*C3H8)* leads to a prediction for the temperature dependence of the rate constant for the unimolecular decomposition of (C3H7+*C4H10)* in the product channel (kp).This analysis indicates that only a gradual transition is expected for k1 and that the actual collision limit is reached only at very low temperatures.
Thermodynamic Stabilities of Phenonium Ions Based on Bromide-Transfer Equilibria in the Gas Phase
Mustanir,Mishima, Masaaki,Fujio, Mizue,Tsuno, Yuho
, p. 1401 - 1407 (2007/10/03)
The thermodynamic stabilities of the phenonium (ethylenebenzenium) ion and ring-substituted derivatives were determined based on the bromide-transfer equilibria in the gas phase. It has been shown that the phenonium ion is 2.4 kcal mol-1 more stable than the t-butyl cation, and that the substituent effect on its stability can be correlated with the Yukawa-Tsuno equation with a ρ value of -12.6 and an r+ of 0.62. An r+ value smaller than unity of the α-cumyl(1-methyl-1-phenylethyl) cation suggested that π-delocalization in the phenonium ion is essentially less effective than through a benzylic π-interaction. On the other hand, the ρ value of -12.6 is distinctly larger than that for the ordinary benzylic carbocation systems, but is comparable to that of the benzenium ion. In addition, it has been found that the r+ value of the phenonium ions in the gas phase is in complete agreement with that for the aryl-assisted process in the acetolysis of 2-arylethyl toluenesulfonates. This suggests that the degree of π-delocalization of the positive charge is the same in the transition state and the intermediate cation. It is concluded that an r+ value of 0.6, which is ranked at a unique position in the continuous spectrum of the resonance demand, is characteristic of the bridged structure of the phenonium ion intermediate and the transition state.
Gas-Phase Reactions of Fe(1-) and Co(1-) with Simple Thiols, Sulfides, and Disulfides by Fourier Transform Mass Spectrometry
Sallans, L.,Lane, K. R.,Freiser, B. S.
, p. 865 - 873 (2007/10/02)
Fe(1-) and Co(1-) are found to react with simple thiols, sulfides, and disulfides.The primary reaction products formed from these metal anions, M(1-), and thiols include MS(1-), MSH(1-), and MSH2(1-) and suggest a mechanism involving initial insertion of the metal into the weak C-S bond.Similarly, C-S insertion is the main mode of attack in the reactions with the sulfides and disulfides, in analogy to what is observed for the reaction of metal cations.Collision-induced dissociation is used to support the proposed structures for the primary products, H-Fe(1-)-SH andFe(1-)-SH.Some of the thermochemical data derived from this study include D0(M(1-)-S)>103 kcal/mol and D0(M(1-)-SH)=83 +/- 9 kcal/mol.Finally, a brief survey of the reactivity of V(1-), Cr(1-), and Mo(1-) with selected organosulfur compounds is also reported.
Precise Determination of Stabilities of Primary, Secondary, and Tertiary Silicenium Ions from Kinetics and Equilibria of Hydride-Transfer Reactions in the Gas Phase. A Quantitative Comparison of the Stabilities of Silicenium and Carbonium Ions in the Gas Phase
Shin, Seung Koo,Beauchamp, J. L.
, p. 900 - 906 (2007/10/02)
Fourier transform ion cyclotron resonance spectroscopy has been used to examine kinetics and equilibria of hydride-transfer reactions of methyl-substituted silanes with various hydrocarbons having well-established gas-phase hydride affinities.The derived hydride affinities, D(R3Si(1+)-H(1-)), for the silicenium ions SiMeH2(1+), SiMe2H(1+), and SiMe3(1+) are 245.9, 230.1, and 220.5 kcal/mol, respectively, to be compared with the values of 270.5, 251.5, and 233.6 kcal/mol for the corresponding carbonium ions.This indicates that the silicenium ions are significantly more stable than the corresponding carbonium ions in the gas phase with H(1-) as a reference base.
Hyperconjugation: Equilibrium Secondary Isotope Effect on the Stability of the tert-Butyl Cation. Kinetics of Thermoneutral Hydride Transfer
Meot-Ner, Michael (Mautner)
, p. 7947 - 7950 (2007/10/02)
The thermochemistry of the hydride transfer equilibrium (CD3)3C(1+) + (CH3)3CH ->/0 = -0.57 +/- 0.02 kcal/mol; ΔS0 = -0.57 +/- 0.08 cal/(mol.K); ΔG0298 = -0.40 +/- 0.07 kcal.mol; and K298 = 1.97 +/- 0.20.The direction of the observed isotope effect is consistent with C-H bond weakening in the ion due to hyperconjugation.The kinetics of the reaction show a slow rate and a large negative temperature coefficient, with k300 = 0.36 and k600 = 0.00625 x 1E-10 cm3 s-1, i.e., reaction efficiencies of about 0.03 to 0.0005.The observed negative temperature coefficient, k = AT-5.8, is larger than those observed for more exothermic hydride transfer reactions.The approach to collison rate is abrupt.
Stabilities of Halonium Ions from a Study of Gas-Phase Equilibria R(1+)+XR'=(RXR')(1+)
Sharma, Dilip K. Sen,Hoejer, Sarah Meza de,Kebarle, Paul
, p. 3757 - 3762 (2007/10/02)
The gas-phase ion equilibria R(1+)+B=RB(1+), where R(1+)=Et(1+), i-Pr(1+), c-Pe(1+), t-Bu(1+), 2-Me-2-Bu(1+), and 2-Nb(1+) and B=CH3Cl, CH2Cl2, CHCl2, CHCl3, SO2F2, CF3H, and CF4 were determined in a pulsed electron beam high pressure mass spectrometer. van't Hoff plots provide ΔG0300, ΔH0, and ΔS0.For the chloronium ions the following trends were observed.The bond energy D(R(1+)-ClR0), where R(1+) changes and R0 is constant, decreases with increasing electronic stabilization of R(1+), i.e., in the order Me(1+), Et(1+), i-Pr(1+), c-Pe(1+), t-Bu(1+), Nb(1+).The same order was observed earlier in this laboratory for D(R(1+)-Cl(1-)), i.e., the chloride affinity of R(1+).However, the changes of D(R(1+)-ClR0) for R(1+)=2-Me-2-Bu(1+), Nb(1+), and t-Bu(1+) are very small.This means that little differential, specific nucleophilic solvation of these ions in solution is to be expected when solvents of low nucleophilicity like CH2Cl2 and SO2ClF are used.The bond energies D(Me(1+)-ClR) increase in the order R=Me, Et, i-Pr, t-Bu.The bond energies D(t-Bu(1+)-B) decrease in the order B=C2H5Cl, CH2Cl2 ca.CH3Cl, CCl3H, SO2F2, CF3H, CF4.The significance of these trends is discussed.
Stability and reactivity of the benzyl and tropylium cations in the gas phase
Sharma, D. K. Sen,Kebarle, P.
, p. 1592 - 1601 (2007/10/02)
A measurement of equilibrium : t-C4H9+ + BzCl = t-C4H9Cl + C7H7+ led to equilibrium constants K4 which are fair agreement with earlier work by Abboud at al.However, the present temperature dependence predicts a ΔS40 which is sufficiently different from that by Abboud et al. to put in question the identification of C7H7+ as Bz+ on the basis of the measured ΔS40 value.Therefore experiments were made to confirm that C7H7+ produced in is Bz+ and not the tropylium cation.A C7H7+ cation was produced by hydrid abstraction from 1,3,5-cycloheptatriene.The behaviour of that C7H7+ ion was entirely different from C7H7+ produced by chloride abstraction from BzCl or hydride abstraction from toluene.While the benzyl derived C7H7+ engaged in a number of reactions like hydride abstraction, chloride abstraction, addition, condensation, etc., the C7H7+ from the heptatriene remained completely unreactive.On this basis the C7H7+ ions were identified as Bz+ and tropylium+, respectively.Rate constants for several reactions of Bz+ were determined.It is concluded that a rearrangement from benzyl to tropylium cations and vice versa does not occur at least up to 300 deg C.The ions also retain their identity if they are produced with considerable internal excitation energy.
