Triphenylpyrylium Tetrafluoroborate-Sensitized Photochemistry of the Terpenes Sabinene, α-Phellandrene, and α- and γ-Terpinene

Climent, María J.; Miranda, Miguel A.; Roth, Heinz D.

doi:10.1002/(sici)1099-0690(200004)2000:8<1563::aid-ejoc1563>3.0.co;2-w

Cited by 8 publications

(3 citation statements)

References 37 publications

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“…The photochemistry of α-phellandrene and α-terpinene parent molecule, 1,3-cyclohexadiene, was also previously investigated by several theoretical and experimental methods. − It has been found that 1,3-cyclohexadiene undergoes exclusively the ring-opening photoreaction . It was also found experimentally that α-phellandrene in solutions may undergo similar ring-opening reactions as well as other types of isomerizations …”

Section: Introductionmentioning

confidence: 99%

Comparative Matrix Isolation Infrared Spectroscopy Study of 1,3- and 1,4-Diene Monoterpenes (α-Phellandrene and γ-Terpinene)

et al. 2011

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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.

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Section: Introductionmentioning

confidence: 99%

Comparative Matrix Isolation Infrared Spectroscopy Study of 1,3- and 1,4-Diene Monoterpenes (α-Phellandrene and γ-Terpinene)

et al. 2011

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“…No Diels−Alder adducts were obtained with a 1,4-disubstituted cyclohexadiene such as α-terpinene ( 5c ), which underwent aromatization as the only observed reaction. Steric hindrance at the attacked CHD positions, together with the much lower oxidation potential (1.2−1.3 V for 5c vs 1.8 for 5a ), make aromatization via the diene cation radical a competitive process (Δ G = 5 kcal mol -1 ). This could also be the reason for the reduced yield of Diels−Alder cycloadduct obtained in the pyrylium salt-photosensitized reaction between 5c and 6a .…”

Section: Resultsmentioning

confidence: 99%

Mechanism of Triplet Photosensitized Diels−Alder Reaction between Indoles and Cyclohexadienes: Theoretical Support for an Adiabatic Pathway

et al. 2006

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Diels-Alder reactions between indoles (InHs) and 1,3-cyclohexadienes (CHDs) were achieved by using aromatic ketones as photosensitizers. For instance, irradiation of deaerated dichloromethane solutions containing benzoylthiophene (BT, 1 mM), indole (20 mM), and phellandrene (40 mM), in the presence of an acylating agent, led to the N-acetylated Diels-Alder cycloadduct in 46% yield (endo:exo ratio of 1.8:1). Energy transfer from the BT triplet to the CHD gave rise to diene dimers as byproducts. Several combinations of CHDs, InHs, and aromatic ketones were tested; the Diels-Alder reaction was found to be a general process, except when the indole nucleus was substituted at position 2 or 7 and when aromatization of the CHD was favored. Theoretical calculations support a stepwise mechanism involving a triplet ternary complex TC(T1), arising from a nearly barrierless reaction between CHD and the 3(BT...HIn) exciplex. All subsequent steps proceed downhill in the triplet excited state, leading to a triplet cycloadduct-sensitizer CA-BT(T1) radical pair. Attempts to detect this species, which is basically an aminyl/BT ketyl radical pair, were performed by laser excitation of a solution containing BT, phellandrene, and indole. The observed transient absorption spectra could be compatible with the added spectra of the expected components of the radical pair.

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“…Triplet recombination of radical ion pairs has been invoked in many systems on the basis of time-resolved optical spectroscopy, − magnetic field effects, , CIDNP spectra, ,,− optoacoustic calorimetry, , or product considerations. − The CIDNP method, in general, can unambiguously identify either the spin multiplicity of a radical (ion) pair precursor or the spin multiplicity of the resulting pair when forming a product. − This feature qualifies the CIDNP technique ideally to detect products of triplet recombination; the basic principles underlying the CIDNP method and the features leading to the recognition of triplet-derived products have been reviewed recently …”

Section: Discussionmentioning

confidence: 99%

Electron-Transfer Photochemistry ofcis- andtrans-1,2-Diphenylcyclopropane with Singlet Acceptors: Recombination of Radical Ion Pairs of Singlet and Triplet Multiplicity

Roth

2003

J. Phys. Chem. A

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Radical ion pairs generated by photoinduced electron transfer from cis-and trans-1,2-diphenylcyclopropane to various singlet or triplet acceptors may undergo back electron transfer in pairs of singlet as well as triplet multiplicity. The pair energy relative to the reactant ground states and an accessible triplet state, respectively, determines whether this process is competitive. For the cis isomer, cis-1• + , an additional reaction, o,o′ coupling, generating 9-methylanthracene, 4, competes with singlet and triplet back electron transfer. This reaction is not accessible in the chloranil reaction for energetic reasons or from the trans isomer on steric grounds.

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Triphenylpyrylium Tetrafluoroborate-Sensitized Photochemistry of the Terpenes Sabinene, α-Phellandrene, and α- and γ-Terpinene

Cited by 8 publications

References 37 publications

Comparative Matrix Isolation Infrared Spectroscopy Study of 1,3- and 1,4-Diene Monoterpenes (α-Phellandrene and γ-Terpinene)

Comparative Matrix Isolation Infrared Spectroscopy Study of 1,3- and 1,4-Diene Monoterpenes (α-Phellandrene and γ-Terpinene)

Mechanism of Triplet Photosensitized Diels−Alder Reaction between Indoles and Cyclohexadienes: Theoretical Support for an Adiabatic Pathway

Electron-Transfer Photochemistry ofcis- andtrans-1,2-Diphenylcyclopropane with Singlet Acceptors: Recombination of Radical Ion Pairs of Singlet and Triplet Multiplicity

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