2612-46-6Relevant articles and documents
photochemical ring-opening reactions are complete in picoseconds: A time-resolved UV resonance raman study of 1,3-cyclohexadiene
Reid, Philip J.,Doig, Stephen J.,Wickham, Steven D.,Mathies, Richard A.
, p. 4754 - 4763 (1993)
Photoproduct formation, vibrational, and conformational relaxation kinetics in the photochemical ring-openings of 1,3-cyclohexadiene (CHD) and α-phellandrene (α-PHE) are determined by picosecond, time-resolved UV Stokes and anti-Stokes resonance Raman spectroscopy. The frequency-doubled output from an amplified, synchronously pumped dye laser system was used to perform transient, two-color resonance Raman Stokes experiments on the photoconversion of CHD to cis-hexatriene (c-HT) and of α-PHE to 3,7-dimcthyl-1,3,5-octatriene (OT). The appearance time of the Stokes scattering from ground-state c-HT is 6 ± 1 ps, while that of OT is 11 ± 2 ps. In both reactions, the photoproduct anti-Stokes ethylenic intensity appears with a time constant of 8 ± 2 ps and decays in 9 ± 2 ps. This similarity demonstrates that the photoproduct appearance and intermolecular vibrational relaxation kinetics are not dramatically affected by the presence of alkyl substituents. Analysis of the photoproduct spectral evolution in the Stokes and anti-Stokes data as well as the observation of Raman lines characteristic of the all-cis conformer in the anti-Stokes data demonstrates that all-cis-HT first appears on the ground-state surface and then undergoes conformational relaxation to produce mono-s-cis-HT with a time constant of 7 ps. The photoproduct anti-Stokes ethylenic and single-bond stretch intensities further demonstrate that the initial photoproduct temperature at 4 ps is 1500 plusmn; 500 K and that the cooling time is 15 ps. This is the first complete analysis of the photoproduct formation, vibrational, and conformational relaxation dynamics characteristic of photochemical pericyclic ring-opening reactions.
Cyclohexadiene ring opening observed with 13 fs resolution: Coherent oscillations confirm the reaction path
Kosma,Trushin,Fuss,Schmid
, p. 172 - 181 (2009)
The third harmonic (270 nm, 11 fs), produced in a short argon cell from Ti-sapphire laser pulses (810 nm, 12 fs), was used to excite 1,3-cyclohexadiene to its lowest ππ* state (1B). Probing was done by transient ionization by the 810 nm pulses, measuring the yields of the parent and a fragment ion. As previously found with 10 times longer pulses, the molecule leaves in two steps (time constants τ1, τ2) from the spectroscopic (1B) to a dark (2A) state and from there (within τ3) to the ground-state surface. In addition to slightly improved values for τ1-τ3, we found in all three locations (L1-L3) on the potentials coherent oscillations, which can be assigned to vibrations. They are stimulated by slopes (driving forces) of the potentials, and the vibrational coordinates indicate the slope directions. From them we can infer the path following the initial excitation: the molecule is first not only accelerated towards CC stretching in the π system but also along a symmetric C=C twist. The latter motion - after some excursion - also erects and stretches the CH2-CH2 bond, so that Woodward-Hoffmann interactions are activated after this delay (in L 2). On leaving L2 (the 1B minimum) around the lower cone of the 1B/2A conical intersection, the wave packet is rapidly accelerated along an antisymmetric coordinate, which breaks the C2 symmetry of the molecule and eventually leads in a ballistic path to (and through) the last (2A/1A) conical intersection. The ring opening begins already on the 1B surface; near the 2A minimum it is already far advanced, but is only completed on the ground-state surface. the Owner Societies.
Comparative matrix isolation infrared spectroscopy study of 1,3- and 1,4-diene monoterpenes (α-phellandrene and γ-terpinene)
Marzec,Reva,Fausto,Proniewicz
, p. 4342 - 4353 (2011)
In the present work, γ-terpinene (a 1,4-diene derivative) and α-phellandrene (1,3-diene derivative) were isolated in cryogenic argon matrices and their structures, vibrational spectra, and photochemistries were characterized with the aid of FTIR spectroscopy and quantum chemical calculations performed at the DFT/B3LYP/6-311++G(d,p) level of approximation. The molecules bear one conformationally relevant internal rotation axis, corresponding to the rotation of the isopropyl group. The calculations provide evidence of three minima on the potential energy surfaces of the studied molecules, where the isopropyl group assumes the trans, gauche+, and gauche conformations (T, G+, G- ). The signatures of all these conformers were identified in the experimental matrix infrared spectra, with the T forms dominating, in agreement with the theoretical predicted abundances in gas phase at room temperature. In situ UV (λ > 200 nm) irradiation of matrix-isolated α-phellandrene led to its isomerization into an open-ring species. The photoproduct was found to exhibit the ZE configuration of its backbone, which to be formed from the reactant molecule does not require extensive structural rearrangements of both the reagent and matrix. γ-Terpinene was photostable when subjected to irradiation under the same experimental conditions. In addition, the liquid compounds at room temperature were also investigated by FTIR-ATR and FT-Raman spectroscopies.
Time-resolved dissociative intense-laser field ionization for probing dynamics: Femtosecond photochemical ring opening of 1,3-cyclohexadiene
Fuss,Schmid,Trushin
, p. 8347 - 8362 (2000)
The concerted photochemical ring opening of 1,3-cyclohexadiene was investigated in the gas phase by low-intensity pumping at 267 nm and subsequent probing by high-intensity photoionization at 800 nm and mass-selective detection of the ion yields. We found five different time constants which can be assigned to traveling times along consecutive parts of the potential energy surfaces. The molecule is first accelerated in the spectroscopic state IB along Franck-Condon active coordinates, then alters direction before changing over to the dark state 2A. All constants including that for leaving the 2A surface are below 100 fs. These times are shorter than appropriate vibrational periods. Such a maximum speed is evidence that the pathway is continuous leading from surface to surface via real crossings (conical intersections) and that the molecule is accelerated right into the outlet of the 2A/1A funnel. On the ground state it arrives as a compact wave packet, indicating a certain degree of coherence. The experimental method promises a high potential for investigating dynamics, since many consecutive phases of the process can be detected. This is because the fragmentation pattern depends on the location on the potential energy surface, so that monitoring several different ions permits to conclude on the population flow through these locations. Ionization at the intensities used is normally considered to be an effect of the electric field of the radiation. But in our case it is enhanced by resonances in the neutral molecule and in particular in the singly positive ion, and it is not sensitive for the length of the molecule (different conformers of the product hexatriene). The ionic resonances explain why hexatriene has a much richer fragmentation pattern than cyclohexadiene. Coulomb explosion is observed from an excited state of a doubly positive ion. Its mechanism is discussed.
Pyrolysis of tricyclic cyclobutane-fused sulfolanes as a route to cis-1,2-divinyl compounds and their Cope-derived products
Aitken, R. Alan,Cadogan, J. I. G.,Gosney, Ian,Humphries, Caroline M.,McLaughlin, Leo M.,Wyse, Stuart J.
, p. 605 - 614 (2007/10/03)
Functionalisation of the double bond of 3-thiabicyclohept-6-ene 3, readily formed by hydrolysis of the cycloadduct 1 of 3-sulfolene and maleic anhydride followed by oxidative bis-decarboxylation, gives tricyclic sulfones 5-7 and 9 with the bicyclo2,4> skeleton. FVP of 3 results in stereospecific extrusion of SO2 to give Z-hexa-1,3,5-triene which undergoes electrocylisation to give cyclohexa-1,3-diene while reaction of 3 with LiAlH4 results in non-stereospecific extrusion to give Z- and E-hexa-1,3,5-triene. Upon FVP the tricyclic sulfones 5-7 and 9 lose SO2 to give 7-membered ring products 16-19 by Cope rearrangement of the initially formed cis-1,2-divinyl intermediates 15. The 1,3-dipolar cycloaddition of nitrile oxides and a nitrone to the double bond of 3 gives tricyclic sulfones with the tricyclo2,6> skeleton and a wider variety of these can be prepared by conventional reactions of 1. Upon FVP these lose SO2 to give stable cis-1,2-divinyl compounds 23, 24, 37-40 and 41-44. The Diels-Alder adducts 48 and 49 have been prepared from 3 and these behave differently upon FVP, losing SO2 and butadiene to give tetrasubstituted benzenes, in the latter case by way of an unexpected tetracyclic intermediate.
