A trans cyclohexene

Bonneau, Roland; Joussot‐Dubien, Jacques; Salem, Lionel; Yarwood, A. J.

doi:10.1021/ja00430a062

Cited by 67 publications

(36 citation statements)

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“…A typical behavior of strained trans-cycloalkenes is to seek relief via protonation and subsequent net addition of solvent across the trans double bond in acidic methanol. 7,9,10,12,13 In our attempt to measure the rate constant for the reaction of transRet-9 with protons in acidic methanol we found a great reduction in signal at 355 nm which is probably due to a reduction in the triplet quantum yield due to a reduced rate of intersystem crossing similar to that found for other retinals when moving from nonpolar to polar solvents. The result is based on the assumption that the lowest energy excited singlet becomes π,π* in character in polar media.…”

Section: Discussionsupporting

confidence: 69%

A Laser Flash Photolysis Study of 11-Cis-Locked Retinal Analogues

et al. 1996

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The photophysics and photochemistry of cis-locked retinal analogues have been investigated by steady-state and by picosecond and nanosecond time-resolved techniques. We have found that retinal analogues locked into the 11,12-cis configuration via bridged 8-and 9-membered rings, Ret-8 and Ret-9, respectively, are restricted in twisting about the 11,12 double bond in the first triplet state, T 1 . The twisting is restricted to different extents depending on the size of the ring. In the case of Ret-8, no geometric isomerization occurs following photoexcitation. This contrasts cis-cyclooctene derivatives which can be photoisomerized to thermodynamically less favored trans-cyclooctene. The result is rationalized by noting that in Ret-8 the ring incorporates four consecutive sp 2 carbons whereas the latter has only two. For Ret-9 which has one extra carbon in the ring, however, "cis-trans isomerization" becomes possible resulting in shorter-lived excited states and a detectable transient on the nanosecond time scale which is assigned to a short-lived (τ ≈ 110 ns) transoid ground state species.

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Section: Discussionsupporting

confidence: 69%

A Laser Flash Photolysis Study of 11-Cis-Locked Retinal Analogues

et al. 1996

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“…While 2-NpC02CH3 in 10 has the well-defined lowest spectroscopic singlet state, that in 12 possesses an unknown electronic state and its quantitative relation with respect to 10 has not been defined. Certain types of photochemical reactions originating from excited states of olefins and enones are susceptible to acid catalysis (30)(31)(32) for which the protonation of an intermediate, suggested to be a twisted state (32)(33)(34)(35), has been proposed as the reactive intermediate. It is tempting to suggest a twisted state of 2-NpC02CH3 to complex 12 without specifying the structures and electronic states.…”

Section: Wavelength (Mu)mentioning

confidence: 99%

The photocycloaddition of naphthoates with acetylacetone; dramatic acid promotions of product quantum yields

Chow¹,

Liu²

1991

Can. J. Chem.

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. Can. J. Chem. 69, 1261Chem. 69, (1991. In acetonitrile and methanol, methyl 1-and methyl 2-naphthoate (1-and 2-NpC02CH3) underwent [2+2] photocycloaddition with acetylacetone (acacH) from a reactive species derived from the lowest spectroscopic singlet excited state to give cyclobutane derivatives such as 9 that ring-opened to afford addition products of acetyl and acetonyl moieties at the 7,8-position for 1-NpC02CH3 (2 and 3) and the 1,2-position for 2-NpC02CH3 (7). Further irradiation of 3 and 7 caused a deep-seated rearrangement of 3 to give 4 and an intramolecular addition of 7 to give the caged product 8. The photocycloaddition quantum yields were increased remarkably in the presence of a trace amount (<0.001 M) of protic acids. For example, the limiting quantum yield of 2 and 3 with Qadducrs = 0.033 (in the absence) increased to Qudducts >0.5 under comparable conditions in the presence of [H2S04] = 0.001 M, approaching the maximum asymptotically at about this concentration; the increases of the quantum yield could not be correlated with H2SO4 concentrations. The acid promotion of the product formation elevated the photocycloaddition to a significantly useful preparative reaction. The photocycloaddition of 2-NpC02CH3 was quenched by tributylamine, dimethylaniline, and methyl iodide, and could not be initiated by typical triplet sensitization. Strong fluorescence of 2-NpC02CH3 at 358 nm in CH3CN was quenched by acetylacetone, tributylamine, dimethylaniline, and methyl iodide, the last of which concurrently enhanced the phosphorescence intensity of 2-NpC02CH3. In the presence of [H2S04] >0.005 M the fluorescence intensity at 358 nm was quenched and a new fluorescence at 470 nm corresponding to protonated '~-N P C O~C H~ appeared. However, in the [H2S04] <0.002 M region, the new fluorescence was not observed, indicating that the protonation scarcely occurred. The Stem-Volmer constant, obtained by the quantum yield monitor, of the 2-NpC02CH3 photocycloaddition with acacH was more than an order of magnitude smaller than that obtained by the quenching of 2-NpC02CH3 fluorescence by acacH. The discrepancies outlined above clearly demonstrate that the reactive intermediate of the photocycloaddition is not the exciplex of the spectroscopic singlet excited species of '~-N~C O~C H~ and acacH, but one that is derived from the exciplex. It is speculated that this unknown reactive intermediate interacts with a proton to promote the photocycloaddition.Key worcls: photocycloaddition of naphthoates, photorearrangement of styryl ketones, acid catalysis of quantum yields, fluorescence of protonated naphthoates, acid enhancement of singlet quenching. 0,001 M) avec une croissance asymptotique qui atteint son maximum autour de cette valeur; on n'a pas pu Ctablir de correlation entre le rendement quantique et la concentration en H2SO4. La catalyse acide de la formation des produits a transform6 la photocycloaddition en une reaction preparative d'une grande utilitt. La photocyloaddition du 2-NpC02CH3 est dtsactivee par la tribu...

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“…[2]. Thus, at a sul-J furic acid concentration of 10-M, where 7, was determined to be 58 ns, +, is -0.1.…”

Section: A Continuous Irradiationsmentioning

confidence: 94%

Mechanism of acid-catalyzed photoaddition of methanol to 3-alkyl2-cyclohexenones

Schuster¹,

Yang²,

Woning³

et al. 1995

Can. J. Chem.

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Contrary to a previous report, it is concluded that formation of methanol adducts to 3-methyl-2-cyclohexenones and of deconjugated enones on irradiation of the enones in acidified solutions proceeds via protonation of the intermediate enone T,T* triplet excited state and not by protonation of a relatively long-lived ground state trans-cyclohexenone. A rate constant for protonation of the triplet state of 3-methyl-2-cyclohexenone by sulfuric acid of 1.7 x lo9 M-I s-' w as determined by laser flash photolysis in ethyl acetate.Based on quantum efficiencies of product formation, a rate constant of ca. 10' M-I s-' was estimated for protonation of the enone triplet by acetic acid, which is too small to cause measurable reduction in the triplet state lifetime in the mM concentration range used in the preparative studies. The intermediate carbocation can be trapped by methanol, or revert to starting enone or the exocyclic deconjugated enone by loss of a proton. Since products revert to starting materials in an acid-catalyzed process, there is an acid concentration at which the yields of products are optimal. This concentration is ca. 6 mM for acetic acid, but is only 0.1 mM for p-toluenesulfonic or sulfuric acids. Product formation could be quenched using I-methylnaphthalene and cyclopentene as triplet quenchers; in the latter case, formation of [2 + 21 photoadducts was observed to compete with formation of methanol adducts. Quenching rate constants were determined by laser flash studies.

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A trans cyclohexene

Cited by 67 publications

References 0 publications

A Laser Flash Photolysis Study of 11-Cis-Locked Retinal Analogues

A Laser Flash Photolysis Study of 11-Cis-Locked Retinal Analogues

The photocycloaddition of naphthoates with acetylacetone; dramatic acid promotions of product quantum yields

Mechanism of acid-catalyzed photoaddition of methanol to 3-alkyl2-cyclohexenones

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