Radical Cations of Monomethyl-Substituted 1,3-Butadienes:  Resonance Raman Spectra and Molecular Orbital Calculations

Keszthelyi, Tamás; Wilbrandt, R.

doi:10.1021/jp9611277

Cited by 8 publications

(9 citation statements)

References 52 publications

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“…The dihedral angle defined by the two ethylene moieties ranges from 56° to 64° from different calculations as shown in Table . Such a nonplanar gauche structure was previously reported for monomethyl-substituted 1,3-butadienes, namely the trans - and cis -1,3-pentadienes . The total energy difference of 18.03 kJ mol -1 between s-trans and gauche suggests a true value rather close to that reported 13 for cis -pentadiene (16.30 kJ mol -1 ).…”

Section: Discussionsupporting

confidence: 82%

“…Studies on the radical cations of polyenes are of general interest toward the understanding of the mechanism of photoconductivity in organic conducting polymers and are of fundamental importance to understand the charge redistribution and structural changes upon oxidation. The spectroscopy of polyenes has consequently been an active field of research for the past decades. − Previously, our group reported studies of a series of butadiene − and its monomethyl substituted ,, radical cations. The present work is an extension to hexadiene to further understand the influence of methyl groups on the carbon skeleton and associated structural changes.…”

Section: Introductionmentioning

confidence: 99%

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Radical Cation of 2,5-Dimethyl-2,4-hexadiene: Resonance Raman Spectrum and Molecular Orbital Calculations

1999

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The radical cation of 2,5-dimethyl-2,4-hexadiene (tetramethylbutadiene, TMB) is studied experimentally by time-resolved resonance Raman (RR) spectroscopy and theoretically by ab initio and density functional theory calculations (UHF, UBLYP, UB3LYP, and CASSCF using the 6-31G(d) basis set). The radical cation is produced in solution at room temperature by laser flash photolysis, and its RR spectrum is excited in resonance with the optically allowed, strong, second electronic 22Au ← 12Bg transition around 365 nm. Calculated transition energies and oscillator strengths agree qualitatively well with reported absorption data. On the basis of the molecular orbital calculations carried out, the observed RR spectrum is assigned to a mixture of s-trans and gauche conformers, the first being strongly predominant. A lower limit of 42 kJ mol-1 is estimated for the torsional energy barrier between the two conformers. Equilibrium geometries and electronic transitions are discussed.

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Section: Discussionsupporting

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Radical Cation of 2,5-Dimethyl-2,4-hexadiene: Resonance Raman Spectrum and Molecular Orbital Calculations

1999

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“…8a). Based upon our calculations of the vibrational energies of the neutral molecule and of the first ionic state of the ion as well as the modes calculated for the neutral ground state by Panachenko et al 54 and for the isoprene radical cation by Keszthelyi and Wilbrandt, 62,63 this structure is assigned to u A (CQC stretching) excitation coupled with u B (CCC deformation). The actual displacements of the atoms are shown in the video files in the additional data section of the electronic publication.…”

Section: He(i) Photoelectron Spectroscopymentioning

confidence: 76%

Valence shell electronic spectroscopy of isoprene studied by theoretical calculations and by electron scattering, photoelectron, and absolute photoabsorption measurements

Martins

Ferreira-Rodrigues

Bernini

et al. 2009

Phys. Chem. Chem. Phys.

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The first ab initio calculations (vertical energies and oscillator strengths) are reported for the neutral electronic transitions of isoprene (2-methyl-1,3-butadiene), CH(2)CHC(CH(3))CH(2). The VUV photoabsorption spectroscopy of the molecule is presented in the energy range 4.6 to 10.8 eV (270-125 nm) with the highest resolution yet reported above 6.05 eV, revealing new spectral features. Valence and Rydberg transitions have been assigned in accordance with the theoretical results and the associated vibronic series have been analysed. The absolute photoabsorption cross sections at energies below 6.89 eV have been used to calculate the photolysis lifetime of isoprene in the upper stratosphere (20-50 km). Electron energy loss spectroscopy (EELS) measurements have enabled further photoabsorption cross sections to be derived in the range 9-28 eV. The first ab initio calculations have been carried out to determine excitation energies to the lowest energy ionic states of isoprene. The calculations are compared with the He(i) photoelectron spectrum (8 to 17 eV) and new vibrational structure is observed in the first photoelectron band.

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“…Apart from general scientific interest, the properties of radical ions in condensed media are also important in the context of materials science and technology. For the past few years we have been involved in the experimental and theoretical investigation of the radical cations of short linear conjugated polyenes [1][2][3][4][5], and of amine-based electron donors such as N,N-dimethylaniline [6] and N,N-dimethylpiperazine [7]. The interest in the properties of polyene radical cations is in part *Corresponding author.…”

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confidence: 99%

The Radical Cation of Bithiophene:An Experimental and TheoreticalStudy

et al. 1999

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The electronic absorption spectrum of the bithiophene radical cation prepared by γ-irradiation in a glassy Freon matrix is presented, together with the Raman spectra excited at 550 and 425 nm, in resonance with the two absorption bands. The 425 nm excited Raman spectrum was also recorded in a room temperature acetonitrile solution, in this case the radical cation was generated via a photoinduced electron transfer reaction. The resonance Raman spectra were interpreted with the help of density functional theory calculations. The results indicate the existence of at least two rotamers of the bithiophene radical cation. The time-domain method was applied to the simultaneous fitting of the absorption and resonance Raman spectra.

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Radical Cations of Monomethyl-Substituted 1,3-Butadienes: Resonance Raman Spectra and Molecular Orbital Calculations

Cited by 8 publications

References 52 publications

Radical Cation of 2,5-Dimethyl-2,4-hexadiene: Resonance Raman Spectrum and Molecular Orbital Calculations

Radical Cation of 2,5-Dimethyl-2,4-hexadiene: Resonance Raman Spectrum and Molecular Orbital Calculations

Valence shell electronic spectroscopy of isoprene studied by theoretical calculations and by electron scattering, photoelectron, and absolute photoabsorption measurements

The Radical Cation of Bithiophene:An Experimental and TheoreticalStudy

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