Tropyl Radical Research Articles

Synthesis of Dibenzoazulene Derivatives via Pd‐Catalyzed (3+2) Alkyne Annulation of Dibenzosuberenone

AbstractNon‐benzenoid PAHs with pentagon/heptagon pairs have unique electronic structures and promising opto‐electronic properties. However, the construction of pentagon/heptagon pair units in these PAHs is challenging. Herein, we developed a Pd‐catalyzed (3+2) alkyne annulation reaction of heptagons, and constructed heptagon/pentagon pairs. The substrate scope is wide and the yield is good to moderate. A series of dibenzoauzlene derivatives were synthesized and their opto‐electronic properties were systematically studied by UV‐vis absorption and cyclic voltammetry. In addition, the dibenzoazulene derivative was further transformed to tropylium cation and tropyl radical, which showed bathochromic shifted absorption and switched aromaticity.

Infrared Spectroscopy of the Tropyl Radical in Helium Droplets.

The infrared spectrum of the X2E2″ tropyl radical has been recorded in the range of the CH-stretch vibrational modes using the helium droplet isolation technique. Two bands are observed at 3053 and 3058 cm–1. The electronic degeneracy of the ground state results in a Jahn–Teller interaction for two of the CH-stretch modes, i.e., first-order interaction for E3′ symmetry modes and second-order interaction for E2′ symmetry modes. The experimentally observed bands are assigned to the E1′ and E3′ CH-stretch modes. The E1′ mode is infrared-active, whereas the E3′ mode is inactive in the absence of the Jahn–Teller interaction. The transition to the upper component of the Jahn–Teller split E3′ mode gains intensity via vibronic coupling, giving rise to the second experimentally observed band.

The thermal decomposition of the benzyl radical in a heated micro-reactor. II. Pyrolysis of the tropyl radical.

Cycloheptatrienyl (tropyl) radical, C7H7, was cleanly produced in the gas-phase, entrained in He or Ne carrier gas, and subjected to a set of flash-pyrolysis micro-reactors. The pyrolysis products resulting from C7H7 were detected and identified by vacuum ultraviolet photoionization mass spectrometry. Complementary product identification was provided by infrared absorption spectroscopy. Pyrolysis pressures in the micro-reactor were roughly 200 Torr and residence times were approximately 100 μs. Thermal cracking of tropyl radical begins at 1100 K and the products from pyrolysis of C7H7 are only acetylene and cyclopentadienyl radicals. Tropyl radicals do not isomerize to benzyl radicals at reactor temperatures up to 1600 K. Heating samples of either cycloheptatriene or norbornadiene never produced tropyl (C7H7) radicals but rather only benzyl (C6H5CH2). The thermal decomposition of benzyl radicals has been reconsidered without participation of tropyl radicals. There are at least three distinct pathways for pyrolysis of benzyl radical: the Benson fragmentation, the methyl-phenyl radical, and the bridgehead norbornadienyl radical. These three pathways account for the majority of the products detected following pyrolysis of all of the isotopomers: C6H5CH2, C6H5CD2, C6D5CH2, and C6H5 (13)CH2. Analysis of the temperature dependence for the pyrolysis of the isotopic species (C6H5CD2, C6D5CH2, and C6H5 (13)CH2) suggests the Benson fragmentation and the norbornadienyl pathways open at reactor temperatures of 1300 K while the methyl-phenyl radical channel becomes active at slightly higher temperatures (1500 K).

Photoionisation of the tropyl radical

We present a study on the photoionisation of the cycloheptatrienyl (tropyl) radical, C7H7, using tunable vacuum ultraviolet synchrotron radiation. Tropyl is generated by flash pyrolysis from bitropyl. Ions and electrons are detected in coincidence, permitting us to record mass-selected photoelectron spectra. The threshold photoelectron spectrum of tropyl, corresponding to the X+ 1A1’ ← X 2E2” transition, reveals an ionisation energy of 6.23 ± 0.02 eV, in good agreement with Rydberg extrapolations, but slightly lower than the value derived from earlier photoelectron spectra. Several vibrations can be resolved and are reassigned to the C–C stretch mode ν16+ and to a combination of ν16+ with the ring breathing mode ν2+. Above 10.55 eV dissociative photoionisation of tropyl is observed, leading to the formation of C5H5+ and C2H2.

Experimental investigation of the Jahn-Teller effect in the ground and excited electronic states of the tropyl radical. Part II. Vibrational analysis of the ÃE3″2-X̃E2″2 electronic transition

Laser-induced fluorescence (LIF) and laser-excited dispersed fluorescence (LEDF) spectra of the cycloheptatrienyl (tropyl) radical C7H7 have been observed under supersonic jet-cooling conditions. Assignment of the LIF excitation spectrum yields detailed information about the A-state vibronic structure. The LEDF emission was collected by pumping different vibronic bands of the A 2E"3<--X 2E"2 electronic spectrum. Analysis of the LEDF spectra yields valuable information about the vibronic levels of the X 2E"2 state. The X- and A-state vibronic structures characterize the Jahn-Teller distortion of the respective potential energy surfaces. A thorough analysis reveals observable Jahn-Teller activity in three of the four e'3 modes for the X 2E"2 state and two of the three e'1 modes for the A 2E"3 state and provides values for their deperturbed vibrational frequencies as well as linear Jahn-Teller coupling constants. The molecular parameters characterizing the Jahn-Teller interaction in the X and A states of C7H7 are compared to theoretical results and to those previously obtained for C5H5 and C6H6+.

Computational investigation of the Jahn-Teller effect in the ground and excited electronic states of the tropyl radical. Part I. Theoretical calculation of spectroscopically observable parameters

Theoretical calculations are performed for the X2E"2 and A 2E"3 states of the cycloheptatrienyl (tropyl) radical C7H7. An important goal of these calculations is to predict and to guide the analysis of the experimentally observed A 2E"3-X 2E"2 electronic spectrum. Vibrational frequencies of the tropyl radical at the conical intersection and stationary points of its X and A state Jahn-Teller distorted potential energy surfaces are given. Spectroscopically obtainable parameters describing the Jahn-Teller effect are calculated for the X and A electronic states. Additionally, the stabilization energies for the X and A states are computed at the CASSCF(7,7) and EOMEA-CCSD levels of theory using various basis sets.

Pseudorotation-driven dynamical structure of the tropyl radical

Despite intensive studies of the neutral tropyl radical, none of its structure, energetics, and vibrational modes are still clear. This system has puzzled scientists for over a decade since one vibrational mode frequency sharply varies from imaginary number 3000i cm-1 to the real number 6000 cm-1, depending on the calculation methods employed. We find that the origin of this peculiar mode is due to the pseudorotation (omegairot) involved in the interconversion of two nearly isoenergetic Jahn-Teller configurations (elongated structure 2B1 and compressed structure 2A2 with C2v symmetry). Here, we first report that this interconversion is not via D7h or C2v symmetry configuration but via Cs symmetry (i.e., by changing the C2v axis). This interconversion barrier is found negligibly small. Thus, the two conformers are considered to be not two different structures but a dynamically identical structure with partial quantum statistical distributions on the potential energy surface. Owing to the nearly barrierless pseudorotation, the overall structure in a short time scale (less than femtosecond) would be Cs-like between 2A2 and 2B1 configurations with small fluctuation of bond distances. However, the dynamical transitions between the 2B1 and 2A2 configurations via 14 different pseudorotation pathways would make the tropyl radical have the effective D7h structure in either a nonshort time scale (greater than femtosecond) or at nonlow temperatures, which explains the high temperature electron spin resonance experiments.

Infrared Spectroscopy of Neutral C7H7 Isomers: Benzyl and Tropyl

The gas-phase infrared absorption spectra of neutral benzyl and tropyl, isomers of formula C7H7, have been measured in the 400-1800 cm-1 spectral region. In addition, a quantum chemical calculation has been performed to model the infrared spectra. For the benzyl radical, the theory shows satisfactory overlap with the experiment, although vibrations involving the CH2 group might be anharmonic. The tropyl radical, which is subject to the Jahn-Teller effect, seems well modeled for the out-of-plane vibrational modes, but less so for the in-plane vibrational modes.

The Tropyl Cation (c-C7H7+) and the Tropyl Radical (c-C7H7)

Ab initio molecular orbital and density functional theory calculations are performed on the tropyl cation (c-C7H7+) and the neutral tropyl radical (c-C7H7). For the tropyl cation the optimized geometry is found to have D7h symmetry, in agreement with experimental results. The harmonic vibrational frequencies for the cation are calculated at various levels of theory and compared to previous assignments, derived from experimental work. It is found that there are a number of discrepancies and the assignments are updated accordingly. Electronic excitation energies for the cation are then calculated. The tropyl radical (2B1) is calculated to have a C2v equilibrium geometry. The harmonic vibrational frequencies are also calculated for this species. Finally, the first adiabatic and vertical ionization energies for c-C7H7 are calculated and found to be in excellent agreement with experiment.

G2(MP2,SVP) study of the relationship between the benzyl and tropyl radicals, and their cation analogues

The calculated heat of formation and ionization energy of the benzyl radical at the G2(MP2,SVP) level differ from recent experimental estimates by just 1 kJ mol −1. The ionization energy of the tropyl radical calculated at this level differs from experiment by 5 kJ mol −1. The heat of formation of tropyl, 281 ± 8 kJ mol −1, is significantly higher than experimental estimates, suggesting the need for experimental re-evaluation. The lowest energy path for rearrangement of the benzyl cation to tropylium proceeds through a single intermediate minimum, the 1-cycloheptatrienyl cation, and requires 272 kJ mol −1.

Excited electronic states of the tropyl (cyclo-C7H7 ) radical

Two-photon electronic absorption spectra of the tropyl radical (cyclic C7H7 ) have been observed by resonance enhanced multiphoton ionization spectroscopy (REMPI) from 415 to 590 nm, corresponding to 34 000–48 000 cm−1. Two Rydberg series are assigned and an ionization potential determined: np, δ=0.35; nf, δ=0.05; I.P.=50 177 cm−1. Vibrational activity of the Rydberg states was observed and the frequencies were found to be similar to the ion: ω2=862 cm−1 (ring breathing); 2ω18=1528 cm−1 (ring bending); and 2ω20=1284 cm−1 (CH out-of-plane bend).

ChemInform Abstract: HELIUM(I) PHOTOELECTRON SPECTRUM OF TROPYL RADICAL

Chemischer InformationsdienstVolume 9, Issue 29 Physical Organic Chemistry ChemInform Abstract: HELIUM(I) PHOTOELECTRON SPECTRUM OF TROPYL RADICAL T. KOENIG, T. KOENIGSearch for more papers by this authorJ. C. CHANG, J. C. CHANGSearch for more papers by this author T. KOENIG, T. KOENIGSearch for more papers by this authorJ. C. CHANG, J. C. CHANGSearch for more papers by this author First published: July 18, 1978 https://doi.org/10.1002/chin.197829044AboutPDF 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. Volume9, Issue29July 18, 1978 RelatedInformation

The One-electron Reduction of Carbonium Ions. VI. The Trapping of the Cycloheptatrienyl Radical with 2-Methyl-2-nitrosopropane in the Course of the Zinc Reduction of the Tropylium Ion

Abstract The zinc reduction of the tropylium ion was carried out in the presence of 2-methyl-2-nitrosopropane (a radical scavenger) in H2O–THF (7:3 by volume) at room temperature. In the reaction mixture with a short reaction time (5 min), t-butyl tropyl nitroxide (II) (a radical-trapping product) was identified by the ESR analysis. α-Phenyl-N-t-butylnitrone (I), which was isolated from the reaction mixture during a prolonged reaction time (30 min), was proved to be derived from the nitroxide II through the hydrogen abstraction by t-butyl nitroxide, which was itself formed from 2-methyl-2-nitrosopropane in situ in the acidic reaction mixture in the presence of zinc powder. The hydrogenation (on Pd/C) of the product mixture for a short reaction time (1 min) gave N-t-butyl-N-cycloheptylhydroxylamine and bicycloheptyl. On the basis of these observations, it is concluded that the primary product of the zinc reduction of the tropylium ion must be the tropyl radical.

One-Electron Reduction of Carbonium Ions. IV. A Kinetic Study on the Reduction of the Substituted Tropylium Ions with Cr(II)

Abstract The one-electron reduction of the unsubstituted, methyl-, ethyl-, isopropyl-, t-butyl-, triphenylmethyl-, and phenyltropylium ions with Cr(II) in a 10% HCl solution gives, quantitatively, the dimer of the corresponding substituted tropyl radical. The measurements of the reaction rate at 25°C exhibit this order of reactivity: t-butyltropylium (k2=7.98 l/g·ion·sec), isopropyltropylium (8.22), ethyltropylium (10.3), methyltropylium (11.1), tropylium (74.0), phenyltropylium (144), and triphenylmethyltropylium (567) ions. The values of log k2 have a linear correlation with the transition energies of the charge-transfer bands observed for these carbonium ions with pyrene, and also with the polarographic half-wave potentials of the respective cations. These correlations indicate that the reactivity of the carbonium ion in the reduction with Cr(II) is determined mainly by the electron affinity inherent in the respective cations. The values of log k2 also have a good linear correlation with the pKR+ values, implying a parallelism between the electron affinity and the electrophilicity of these stable carbonium ions.

Pulsradiolytische Untersuchung des Tropylium-Ions, des Tropylcarbinols und des Tropilidens in wäßriger Lösung / Pulse Radiolysis of the Tropylium-ion, Tropylcarbinol and Tropilidene in Aqueous Solution

The tropylium-ion, C7H7⊕, is reduced by the H atom to yield the tropyl radical C7H7. C7H7 absorbs at 3150 Å with ε=2800 mole-1 l cm-1. The rate constant of the reaction C7H7 + +H → C7H7 + H3O⨁ is (7 ± 2) 109 mole-1 l s-1. C7H7⨁ is also reduced by α-alcohol radicals but not by β-alcohol radicals. Tropylcarbinol C7H7OH reacts with eaq ⊖ with k= (6 ± 2) 109 mole-1 l s-1. The product is non conducting and absorbs at 3150 Å with ε=4200 mole-1 l cm -1. This absorption is attributed to the hydroxycycloheptadienyl radical.

One-Electron Reduction of Carbonium Ions. II. Reduction of the Tropylium Ion and the Triphenylmethyl Cation with Metallic Powders and Metallic Ions

Abstract The reaction of tropylium fluoroborate in an aqueous solution has been carried out at room temperature with powders of various metals (Mg, Al, Mn, Zn, Cr, Fe, Cd, Co, Ni, Sn, Pb, Sb, Cu, Hg, and Ag) under heterogeneous conditions and with several metallic ions (Cr(II), Ti(III), Sn(II), Cu(I), Fe(II), Fe(III), Hg(I), Hg(II), and Ag(I)) in a homogeneous solution. All these reagents, except Ag, Fe(III), Hg(I), Hg(II), and Ag(I), reduce with ease the tropylium ion to give the tropyl radical, which then rapidly couples to bitropyl; their reducing powers, estimated by comparing the yields of bitropyl under the same reaction conditions, correlate with their oxidation electrode potentials and oxidation-reduction potentials. The ferric ion, the mercurous ion, the mercuric ion, and the silver ion afforded no bitropyl, but only an oxidation product of the tropylium ion, i.e., benzaldehyde. Silver powder gives neither a reduction nor an oxidation product under these reaction conditions. The reduction has also been carried out in an acetonitrile solution, and the reducibility of tropylium fluoroborate with powders of Zn, Fe, Ni, Sb, Cu, and Ag has been compared with that of triphenylmethyl fluoroborate under heterogeneous conditions. Both the tropylium ion and the triphenylmethyl cation are smoothly reduced by Zn, Fe, Ni, Sb, and Cu in this solvent. The tropylium ion, however, is not reduced by silver powder, while the triphenylmethyl cation is reduced to the triphenylmethyl radical. This greater reducibility of the triphenylmethyl cation is consistent with what could be anticipated from the data of half-wave potentials, ionization potentials, and H.M.O. calculation reported with respect to these two carbonium ions.

A Study of the Pyrolysis of Toluene Using 14C as a Tracer

Abstract The pyrolysis of toluene-1-14C was carried out by means of the semi-flow method at 800 and at 1000°C in the presence of the registers of porcelain, and the distributions of the radioactive carbon in gaseous products and that of the deposited carbon were determined. The molar c.p.m. of methane and that of a mixture of C2-compounds were about 1/20 of and twice the molar c.p.m. of the original toluene respectively, while the c.p.m. per gram-atom of the deposited carbon was about twice that of toluene, when the temperature of reaction was 800°C. In the case of the reaction at 1000°C, the c.p.m. per gram-atom of carbon of each product was found to be practically equal to that of the original toluene. It was proposed that methane is formed by the removal of the methyl group of toluene, and that the main source of the carbon of C2-compounds and the deposited carbon is the 1-carbon of toluene. The equalization of the radioactive carbon in every product at a high temperature was interpreted by assuming that the tropyl radical is formed as an intermediate after the formation of the phenyl radical in the initial stage of the reaction.

The high resolution absorption spectroscopy of aromatic free radicals

The flash photolysis of aromatic molecules at high resolution, using long path lengths, has enabled us to observe a wealth of new spectra. In particular the weak, long wavelength transition of benzyl and substituted benzyl radicals has been observed. Their assignment to benzyl, rather than, for example, to an isomeric tropyl radical is confirmed and the structure of the spectrum is discussed. Brief reference is made to other transient spectra which we have recently recorded, including the spectrum of the phenyl radical.

Spectrum of the tropyl radical

Download options Please wait... Article information DOI https://doi.org/10.1039/DF9633500196 Article type Paper Download Citation Discuss. Faraday Soc., 1963,35, 196-200 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Spectrum of the tropyl radical B. A. Thrush and J. J. Zwolenik, Discuss. Faraday Soc., 1963, 35, 196 DOI: 10.1039/DF9633500196 To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author B. A. Thrush J. J. Zwolenik

Evidence for the formation of the tropyl radical in liquid solution

Click to increase image sizeClick to decrease image size Additional informationNotes on contributorsJ. dos Santos-VeigaOn leave from the University of Coimbra, Portugal.