26811-28-9Relevant academic research and scientific papers
Threshold Formation of Benzylium (Bz+) and Tropylium (Tr+) from Toluene. Nonstatistical Behavior in Franck-Condon Gaps
Lifshitz, Chava,Gotkis, Yehiel,Laskin, Julia,Ioffe, Alexander,Shaik, Sason
, p. 12291 - 12295 (1993)
Benzylium (Bz+) and tropylium (Tr+) ion formation from toluene-h8 and toluene-α-d3 were studied by time-resolved photoionization mass spectrometry (TPIMS).Bz+ was distinguished from Tr+ through its ion/molecule reaction with toluene, which converts it quantitatively to C8H9+.The appearance energies (AE's) at 0 K of C7H7+ without ion trapping (11.5 eV) and of Bz+ with ion trapping (11.1 eV) are in excellent agreement with predictions by time-resolved photodissociation (TRPD).The structure observed at photon energies below 11.1 eV in the Bz+ photoionization efficiency curve is ascribed to autoionizing Rydberg states converging to the third ionization energy in toluene.These states, which reside in a Franck-Condon gap, dissociate in competition with autoionization.This dissociation is a non-RRKM process forming Bz+, in preference to Tr+, and is made possible energetically by virtue of the thermal energy at the temperature of the experiment (298 K).H/D loss ratios for toluene-α-d3 demonstrate complete isotopic scrambling and an energy dependent isotope effect.The H/D ratio stays constant below 11.1 eV, demonstrating that AE0 K (Tr+) = 11.1 eV and that there is equality of the AE's of the two C7H7+ isomers within experimental error.The preferential, nonstatistical, formation of Bz+ over Tr+ below ca. 11.1 eV is given further proof by the observation of an increased direct CD2+ transfer probability from C6H5CD2+ to C6H5CD3.These results, combined with previously published ab initio calculations which demonstrated a reverse activation energy for the Tr+ exit channel, explain why there is no energy range in which there is pure Tr+ formation from toluene, under either photoionization or electron ionization conditions, although Tr+ is ca. 11 kcal/mol more stable than Bz+.
Ultraviolet absorption spectra and photochemical rearrangements of benzyl and tropylium cations in solid argon
Andrews, Lester,Keelan, Brian W.
, p. 99 - 103 (1981)
New ultraviolet absorptions were produced at 353 and 263 nm upon cocondensation of benzyl bromide vapor with excess argon from an open-ended discharge tube on a sapphire plate at 22 K. Agreement with the pulse-radiolysis solution spectrum of benzyl cation
Time-Resolved Photodissociation Rates and Kinetic Modeling for Unimolecular Dissociations of Iodotoluene Ions
Lin, Chuan Yuan,Dunbar, Robert C.
, p. 1369 - 1375 (1994)
Time-resolved photodissociation rate measurements are reported for the unimolecular dissociation of the three iodotoluene ion isomers at two values of internal energy (2.54 and 2.67 eV).For the para isomer, the rate constants are in agreement with previous experimental information.The meta isomer is roughly similar to para, but the ortho isomer dissociates roughly 5 times faster at the same internal energies.These new data, along with prior results, are fitted into a comprehensive two-channel model of the dissociation kinetics, assuming competitive dissociation to form tolyl ions, and either benzyl or tropylium ions.Activation energies and entropies are assigned to both dissociation channels for each isomer.This two-channel model accounts satisfactorily for most of the experimental information available about these dissociation processes, and possible explanations are advanched to explain discrepant data.
A Reinvestigation of the Collisional Activation Mass Spectra of + Ion Mixtures
Buschek, J. M.,Ridal, J. J.,Holmes, J. L.
, p. 543 - 549 (1988)
The collisional activation (CA) mass spectra of the two isomeric + ions, benzyl and tropyl, have been reassessed.The structure-characteristic feature of their CA mass spectra, the m/z 77:74 abundance ratio, has been confirmed as 3.15 +/-
Reaction of O2+ + C8H10 (ethylbenzene) as a function of pressure and temperature: A study of the collisional stabilization of the reactant intermediate
Viggiano,Miller, Thomas M.,Williams, Skip,Arnold, Susan T.,Seeley, John V.,Friedman, Jeffrey F.
, p. 11917 - 11922 (2007/10/03)
Rate constants and branching fractions for the reaction of O2+ with C8H10 (ethylbenzene) have been measured in the recently upgraded turbulent ion flow tube (TIFT) and are reported here as a function of temperat
Reactivity in acid-catalyzed carbon-carbon heterolysis
Cao, Weiguo,Erden, Ihsan,Grow, Richard H.,Keeffe, James R.,Song, Jiangao,Trudell, Mary B.,Wadsworth, Teri L.,Xu, Fu-Pei,Zheng, Ji-Bin
, p. 1009 - 1034 (2007/10/03)
Equilibrium and rate constants have been determined for the acid-catalyzed heterolysis of two alcohols, 9-xanthydrol and p-anisyldiphenylmethanol, and two sulfides, (9-xanthyl) methyl sulfide and (7-tropyl) methyl sulfide. These data together with literature information are compared with rate constants for acid-catalyzed C-C heterolysis of several (9-xanthyl) compounds, (7-tropyl) compounds, a set of 3-arylcyclobutanones, and two 2-arylnitrocyclopropanes, all of which fragment to carbocations plus a carbon-centered nucleofuge. The fragmentation mechanisms are shown to be A1 or A1(ion pair) except for the 2-arylnitrocyclopropanes which cleave in trifluoroacetic acid by a concerted mechanism. Rate comparisons among several unstrained substrate sets indicate that O-centered nucleofuges undergo acid-catalyzed heterolysis ca. 103-104 faster than S-centered nucleofuges and ca. 109-1014 faster than the C-centered nucleofuges used here. Factors assisting C-C heterolysis (and their effectiveness) include the acidity of the medium (strong); the basicity and nucleofugality of the nucleofuge (moderate); the stability of the electrofugic carbocation (strong); and relief of ring strain (enormous). Compared with acyclic cleavages, rate accelerations worth ca. 15 kcal/mol (for cyclobutanones) and ca. 27 kcal/mol (for nitrocyclopropanes) are found. These effects are discussed in terms of transition-state structure, aided by computational evidence.
Site of Gas-phase Methylation of 1-Phenyl-2-aminopropane
Zappey, Herman,Fokkens, Roel H.,Ingemann, Steen,Nibbering, Nico M. M.,Florencio, Helena
, p. 587 - 594 (2007/10/02)
The regioselectivity of methyl cation transfer from (CH3)2F(1+), (CH3)2Cl(1+) and (CH3)3O(1+) to 1-phenyl-2-aminopropane was studied by Fourier transform ion cyclotron resonance in combination with collision-induced dissociation and neutralization-reionization mass spectrometry of the stable (1+) ions formed in a chemical ionization source.The (CH3)2F(1+) ion transfers a methyl cation to the NH2 group and the phenyl ring with almost equal probability.Predominant CH3(1+) transfer to the NH2 group is observed for the (CH3)2Cl(1+) ion whereas the (CH3)3O(1+) ion reacts almost exclusively at the amino group.The preference for m ethylation at NH2 is discussed in terms of a lower methyl cation affinity of the phenyl ring than of the amino group and the existence of an energy barrier for methylation of the phenyl moiety.
Heterolysis and homolysis energies for some carbon-oxygen bonds
Arnett, Edward M.,Amarnath, Kalyani,Harvey, Noel G.,Venimadhavan, Sampath
, p. 7346 - 7353 (2007/10/02)
Methods described previously for obtaining heterolysis (ΔHhet) and homolysis (ΔHhomo) enthalpies for bonds that can be cleaved to produce resonance-stabilized carbenium ions, anions, and radicals are extended to the study of carbon-oxygen bonds through the reactions of resonance-stabilized carbenium ions with substituted phenoxide ions. Titration calorimetry was used to obtain the heat of heterolysis, and the second-harmonic ac voltammetry (SHACV) method was used to obtain reversible oxidation potentials for the anions. In several cases, the electrode reactions were so fast that reversible potentials were obtained only with the greatest difficulty. Nonetheless, there is remarkably good agreement between these oxidation potentials for phenoxide ions obtained by electrochemical methods in sulfolane solution and those reported by others using entirely different techniques in different media. Such agreement provides unprecedented evidence for the soundness of the various methods used to study redox potentials of organic ions and radicals. As before, a wide variety of correlations was tested between ΔHhet and ΔHhomo. These two properties showed little correlation with each other, but ΔHhet gave good correlations between many properties for which neutral species are converted into ions or vice versa, such as redox potentials of both types of ions, the pKas of the anions, or the free energies of electron transfer. In contrast to the earlier study of cleavage to carbanions and carbenium ions, the present ΔHhet values are predicted well by a general equation that employs the pKR+ of the carbenium ion (without modification) and the pKa of the phenol. The improvement is consistent with the fact that the cleavage of carbon-oxygen bonds of the triarylcarbinols used to establish the pKR+ stability scale is a more appropriate model for the heterolysis of carbon-oxygen bonds in sulfolane at 25°C than it is for the cleavage of carbon-carbon bonds under the same conditions.
Elementary Photoprocesses in Benzene Clusters
Schriver, K. E.,Camarena, A. M.,Hahn, M. Y.,Paguia, A. J.,Whetten, R. L.
, p. 1786 - 1789 (2007/10/02)
The article reports the use of the resonant two-photon ionization technique to selectively excite a molecular ion within a cluster and observe the dynamical outcome.We have excited clusters containing up to 14 benzene molecules to energies of 10.00 or 12.84 eV and measured the probability that an initially formed C6H6+ attacks a neighboring benzene unit of the cluster according to the vapor-phase reaction C6H6+ + C6H6 -> C7H7+ + C5H5, ΔH = 0.63 eV.The C5H5 radical is expelled from the cluster.At either energy excitation proceeds through an X112 vibrational level of benzene (X = 6 or 8) but in the latter case the benzene cation is also produced electronically excited.Accordingly, at low-energy excitation the above pathway is entirely absent, while the 12.84-eV excitation leads to reaction with a probability increasing with cluster size, as predicted by solvation models.This result makes it appear quite likely that >12-eV excitation of condensed benzene will lead to transient tropylium ion centers for conduction electrons, accompained by variable trapping of C5H5.
