Photoelektronenspektren und konformation von 1,1'-bipyrroylen

Flitsch, Wilhelm; Peeters, Hermann; Schulten, W.; Rademacher, Paul

doi:10.1016/0040-4020(78)89042-5

Cited by 26 publications

(9 citation statements)

References 9 publications

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“…Nonetheless, the available evidence suggests that the exit channel barrier is sufficiently low that molecules excited to the 1 1 A 2 state can surmount it-either directly, or by H atom tunnelling. As discussed above, the inductive effect of the two CH 3 groups in 2,5-DMP should stabilise the cation (a prediction born out by photoelectron spectroscopy 21 ), and thus lower the relative energies of all Rydberg states, including the 1 1 A 2 state in the vertical Franck-Condon region. Such expectations are confirmed by the absorption spectrum (Fig.…”

Section: Discussionmentioning

confidence: 92%

High resolution photofragment translational spectroscopy studies of the near ultraviolet photolysis of 2,5-dimethylpyrrole

Cronin¹,

Nix²,

Devine³

et al. 2006

Phys. Chem. Chem. Phys.

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The photodissociation dynamics of 2,5-dimethylpyrrole (2,5-DMP) has been investigated following excitation at 193.3 nm and at many near ultraviolet (UV) wavelengths in the range 244 < lambda(phot) < 282 nm using H Rydberg atom photofragment translational spectroscopy (PTS). Complementary UV absorption and, at the longest excitation wavelengths, one photon resonant multiphoton ionisation spectra of 2,5-DMP are reported also; analysis of the latter highlights the role of methyl torsional motions in promoting the parent absorption. The deduced fragmentation dynamics show parallels with that reported recently (B. Cronin, M. G. D. Nix, R. H. Qadiri and M. N. R. Ashfold, Phys. Chem. Chem. Phys., 2004, 6, 5031) for the bare pyrrole molecule. Excitation at the longer wavelengths leads to (vibronically induced) population of the 1(1)A(2)(pisigma*) excited state of 2,5-DMP, but once lambda(phot) decreases to approximately 250 nm stronger, dipole allowed transitions start to become apparent in the parent absorption. All total kinetic energy release (TKER) spectra of the H + 2,5-dimethylpyrrolyl (2,5-DMPyl) fragments measured at lambda(phot)> or=244 nm show a structured fast component, many of which are dominated by a peak with TKER approximately 5100 cm(-1); analysis of this structure reveals lambda(phot) dependent population of selected vibrational levels of 2,5-DMPyl, and enables determination of the N-H bond strength in 2,5-DMP: D(0) = 30 530 +/- 100 cm(-1). Two classes of behaviour are proposed to account for details of the observed energy partitioning. Both assume that N-H bond fission involves passage over (or tunnelling through) a small exit channel barrier on the 1(1)A(2) potential energy surface, but differ according to the vibrational energy content of the photo-prepared molecules. Specific parent out-of-plane skeletal modes that promote the 1(1)A(2)-X(1)A(1) absorption appear to evolve adiabatically into the corresponding vibrations of the 2,5-DMPyl products. Methyl torsions can also promote the 1(1)A(2)<-- X(1)A(1) absorption in 2,5-DMP, and provide a means of populating a much higher density of excited vibrational levels than in pyrrole. Such excited levels are deduced to dissociate by redistributing the minimum amount of internal energy necessary to overcome the exit channel barrier in the N-H dissociation coordinate. Coupling with the ground state surface via a conical intersection at extended N-H bond lengths is proposed as a further mechanism for modest translational --> vibrational energy transfer within the separating products. The parent absorption cross-section increases considerably at wavelengths approximately 250 nm, and PTS spectra recorded at lambda(phot)< or = 254 nm display a second, unstructured, peak at lower TKER. As in pyrrole, this slower component is attributed to H atoms from the unimolecular decay of highly vibrationally excited ground state molecules formed via radiationless decay from photo-excited states lying above the 1(1)A(2) state.

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Section: Discussionmentioning

confidence: 92%

High resolution photofragment translational spectroscopy studies of the near ultraviolet photolysis of 2,5-dimethylpyrrole

Cronin¹,

Nix²,

Devine³

et al. 2006

Phys. Chem. Chem. Phys.

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“…1, selected bond lengths and angles in Table 1) exhibits an interplanar angle of the pyrrole fragments of 92.4Њ thus confirming the predictions both of MO calculations and PE experiments. 5 The N,N-distance of 1.378(2) Å lies near the upper end of the range expected for sp 2 -hybridized nitrogen atoms. There are no significant differences in the geometry of the five-membered rings (averaged values: N-C α 1.383, C α -C β 1.365, C β -C βЈ 1.431 Å, C α -N-C αЈ 110.9Њ) as compared to the structure of 9 (averaged values of the uncoordinated pyrrole rings: N-C α 1.368, C α -C β 1.354, C β -C βЈ 1.425 Å, C α -N-C αЈ 109.8Њ).…”

Section: Synthesis and Structure Of 22ј33ј44ј55ј-octamethyl-11јbipyrrolementioning

confidence: 86%

“…1 The interest in 1,1Ј-bipyrroles focuses on the formation of pyrrolyl radicals (3) 2-4 as well as on studies concerning their structure and bonding. 5 A special topic deals with the chemistry of hydrazine-bridged annulenes. 6 As part of our investigations on pyrrolyl and pyrrole metal π-complexes 7 we are interested in reductive N,N-bond fission as a route to new azacyclopentadienyl metal complexes.…”

Section: Introductionmentioning

confidence: 99%

Synthesis, oxidation and protonation of octamethyl-1,1′-bipyrrole

Kühn

Kotowski

Steimann

et al. 2000

J. Chem. Soc., Perkin Trans. 2

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“…We have already mentioned the crystallographic data of 4,4'-bi-1,2,4-triazole, 1 (2 1). From the splittings of the n2-ionizations of the photoelectron spectrum of 1,11-bipyrrole it has been also concluded that this compound has the most stable conformation at 90" (17).…”

Section: In Inmentioning

confidence: 99%

“…To the best of our knowledge, only 1 , l '-bipyrrole has been calculated by Galasso (1 6) and by Flitsch, Rademacher and co-workers in order to assign its photoelectron spectrum (17). In the former paper, the E.H.T.…”

Section: Introductionmentioning

confidence: 99%

N,N-Linked biazoles. III. MNDO calculations on the conformation of N,N-linked biazoles and their quaternary salts

Castellanos¹,

Olivella²,

Roca³

et al. 1984

Can. J. Chem.

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A theoretical study of fourteen N,N-linked biazoles has been carried out using the MNDO method with full optimization of the geometries. The variation of energy as a function of the conformation around the central N—N bond shows in all cases the higher stability of the orthogonal or near-orthogonal form. The contribution of the three main types of "ortho" interactions [Formula: see text] and the effect of quaternization have been evaluated. Of the electronic properties calculated, one must emphasize the excellent agreement of dipole moments with experimental values.

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Photoelektronenspektren und konformation von 1,1'-bipyrroylen

Cited by 26 publications

References 9 publications

High resolution photofragment translational spectroscopy studies of the near ultraviolet photolysis of 2,5-dimethylpyrrole

High resolution photofragment translational spectroscopy studies of the near ultraviolet photolysis of 2,5-dimethylpyrrole

Synthesis, oxidation and protonation of octamethyl-1,1′-bipyrrole

N,N-Linked biazoles. III. MNDO calculations on the conformation of N,N-linked biazoles and their quaternary salts

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