Cyclobutadiene. 3. Photolysis of matrix-isolated carbon-13-labeled bicyclopyranones

Pong, Richard G. S.; Huang, Bo; Laureni, J.; Krantz, A.

doi:10.1021/ja00454a043

Cited by 42 publications

(29 citation statements)

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“…6 a A-B-C is the angle between bonds A-C and B-C. upon irradiation of the matrix with UV (λ > 235 nm) light. [18]. In the high frequency spectral region, the three intense methyl stretching bands were observed at 2973.7, 2931.2 and 2907.6 cm −1 , while the C ring -H asymmetric stretching was found at 3072.4 cm −1 , also in good agreement with the theoretical predictions (see Table 3.…”

Section: Resultssupporting

confidence: 85%

4,6-Dimethyl-α-pyrone: a matrix isolation study of the photochemical generation of conjugated ketene, Dewar valence isomer and 1,3-dimethyl-cyclobutadiene

Breda

Lapiński

Reva

et al. 2004

Journal of Photochemistry and Photobiology A: Chemistry

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A combined matrix isolation and molecular orbital study of the vibrational spectra and photochemistry of 4,6-dimethyl-␣-pyrone (DMAP) was undertaken. Two types of photoreactions: ring opening leading to conjugated ketene and valence isomerization to the Dewar form (1,5-dimethyl-2-oxa-3-oxobicyclo[2.2.0]hex-5-ene; DOOBH), occurred upon UV (λ > 315 nm) irradiation. The latter reaction was efficient, whereas aldehyde-ketene was produced only in little amounts. In addition to the IR spectroscopic study of DMAP, the full mid-IR spectrum of the photoproduced DOOBH is reported and interpreted. Observation of 1,3-dimethyl-cyclobutadiene (DMCB), created by shorter wavelength UV irradiation (λ > 235 nm) of DOOBH, is reported for the first time. In the matrices, DMCB forms a complex with CO 2 ; the structure and IR absorption features of this cage confined DMCB-CO 2 complex are also investigated.

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Section: Resultssupporting

confidence: 85%

4,6-Dimethyl-α-pyrone: a matrix isolation study of the photochemical generation of conjugated ketene, Dewar valence isomer and 1,3-dimethyl-cyclobutadiene

Breda

Lapiński

Reva

et al. 2004

Journal of Photochemistry and Photobiology A: Chemistry

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“…However, the spectroscopic results doubtlessly show that the photochemistry of matrix isolated ␣-pyridil is considerably simpler than it could be expected. In fact, none of the characteristic bands of carbon monoxide {at 2138 (Ar) or 2133 (Xe) cm −1 [66,67] [51,70]} were observed in the spectra of the photolysed matrix, implying that all putative reaction steps involving the production of these species did not take place and could be promptly discarded. This significantly reduces the number of possible photoproducts and, in particular, excludes the intercarbonyl bond cleavage reaction path and all reactions putatively occurring after formation of the pyridine valence isomers' based products.…”

Section: Infrared Spectroscopy: Analysis Of the Matrix Isolation Specmentioning

confidence: 99%

Low temperature IR spectroscopy and photochemistry of matrix-isolated α-pyridil

Lopes

Gómez‐Zavaglia

Fausto

2008

Journal of Photochemistry and Photobiology A: Chemistry

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2 ] has been isolated in low temperature argon and xenon matrices and studied by FTIR spectroscopy, supported by DFT(B3LYP)/6-311++G(d,p) calculations. Calculations predicted the existence of three different conformers exhibiting skewed conformations around the intercarbonyl bond and the two C 5 H 4 N C( O) fragments nearly planar. The two higher energy forms, TCG and CCSk were estimated theoretically to be, respectively, 21.0 and 35.1 kJ mol −1 higher in energy than the most stable form, TTG. In consonance with the relatively high energies predicted by the calculations for the two less stable conformers of ␣-pyridil, only the most stable conformer was found spectroscopically to be present in the studied matrices. Infrared spectra obtained for the neat low temperature amorphous and crystalline states reveals that the TTG conformer is also the sole conformer present in these phases. UV irradiation ( > 235 nm) of matrix-isolated ␣-pyridil led to its isomerization into unusual molecular species bearing Hückel-type pyridine (aza-benzvalene) rings.

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“…Formation of the thioaldehyde-ketene species can be possible by an intramolecular hydrogen-transfer reaction analogous to that occurring in the conjugated aldehyde-ketene generated from a-pyrone. [11] Only one of the TK conformers (that depicted in Scheme 2 and TK4 in Figure S01 in the Suppoting Information) is well aligned for intramolecular H-atom abstraction. The thioaldehyde-ketene is then initially produced in the conformation depicted in Scheme 2 (conformer TA4 in Figure S02), which subsequently isomerizes to other TA conformational states.…”

mentioning

confidence: 99%

“…Photoproduction of the Dewar isomer of a-pyrone is a well-known process and has been used to generate cyclobutadiene (together with CO 2 ). [3,[11][12][13] Indeed, the relative efficiency of the Dewar isomerization and open-ring reaction leading to the conjugated aldehyde-ketene was found to depend strongly on the presence of substituents in the pyrone ring. For example, in the unsubstituted a-pyrone the kinetically pre- Figure 1.…”

mentioning

confidence: 99%

“…The fingerprint region of the infrared spectrum of pyran-2-thione: A) theoretical spectrum calculated at the B3LYP/6-311 + + G(d,p) level; B) experimental spectrum of monomers of the compound isolated in an argon matrix at 10 K. Theoretical frequencies were scaled using a factor equal to 0.978. ferred reaction is the ring-opening process, while in 4,6-dimethyl-a-pyrone, 4-hydroxy-6-methyl-a-pyrone and 4-methoxy-6-methyl-a-pyrone the Dewar isomerization strongly dominates. [3,4,[11][12][13][14][15] Herein, the possibility of occurrence of a similar process in pyran-2-thione, leading to photoproduction of cyclobutadiene and COS, was also considered. However, no signs of absorptions due to either cyclobutadiene and COS or the Dewar isomer could be found in the spectra of the pyran-2-thione irradiated matrices, clearly indicating that under the present conditions this process does not take place.…”

mentioning

confidence: 99%

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Photochemical α‐Cleavage in Pyran‐2‐thione: Generation of Aldehyde–Thioketene and Thioaldehyde–Ketene Photoproducts

et al. 2005

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The photochemical ring-opening reaction leading to cleavage of the CÀO a-bond in a-pyrones, and other similar photoreactions observed in closely related unstrained cyclic carbonyl compounds such as 2,4-cyclohexadienones [1] and pyrimidinones, [2] are well documented. In the case of a-pyrones (Scheme 1), because of the high reactivity of the ketene moiety, the open-ring conjugated ketene photoproducts can be stabilized only in solid, low-temperature inert matrices. [3,4] The intense, characteristic infrared band due to the antisymmetric stretching vibration of the ÀC=C=O group, appearing in the 2140-2130 cm À1 spectral region, facilitates the identification of ketene photoproducts. Open-ring conjugated ketenes are usually presented as structures shown in Scheme 1. However, it is improbable that such isomers of conjugated ketenes could be stabilized under any conditions. It was recently demonstrated [3] that these forms revert barrierlessly to stable, closed-ring structures. The detailed structural analysis carried out for the conjugated aldehyde-ketene generated upon UV irradiation of a-pyrone strongly suggests [3] that the isomers, which are stabilized in a matrix, must adopt a conformation with at least one of the groups rotated around a single or double bond of the openchain structure.Contrarily to the carbonyl compounds, the photochemical cleavage of an a-bond is believed not to occur for thiocarbonyl compounds, [5] though Pirkle et al. reported [6] pyranthiones that underwent thermal rearrangements (similar to that depicted on Scheme 1) during pyrolysis at elevated temperatures. The known exceptional cases of photochemical a-cleavage concern only the species with C=S groups directly attached to small (three-or four-membered), strained rings. [7] Herein, we report the experimental observation of the photochemical ring opening, by cleavage of the CÀO a-bond in pyran-2-thione (Scheme 2). In this compound the thiocarbonyl group is attached to a relaxed, six-membered ring.The unimolecular photochemistry of pyran-2-thione was studied by a combined usage of the matrix isolation technique and FTIR spectroscopy. The infrared spectral signatures of the primary photogenerated aldehyde-thioketene (TK) isomeric forms, as well as those of the secondary products, thioaldehyde-ketene (TA) isomers, were assigned on the basis of theoretical calculations carried out at the B3 LYP/6-311 + + G(d,p) level.In the matrix isolation experiments, a sample of pyran-2-thione [8] (PT) was placed into a glass tube protected against light and connected to the chamber of the cryostat with a needle valve. The vapor of the compound was introduced into the cryostat chamber through the needle valve together with large excess of the host matrix gas (argon N60, Air Liquide) coming from a separate line. A cold (10 K) CsI window mounted on the tip of an APD Cryogenics DE-202 A closed-cycle helium refrigerator was used as optical substrate. Care was taken to keep the guest-to-host ratio in the matrixes low enough to avoid association. The matrices we...

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Cyclobutadiene. 3. Photolysis of matrix-isolated carbon-13-labeled bicyclopyranones

Cited by 42 publications

References 0 publications

4,6-Dimethyl-α-pyrone: a matrix isolation study of the photochemical generation of conjugated ketene, Dewar valence isomer and 1,3-dimethyl-cyclobutadiene

4,6-Dimethyl-α-pyrone: a matrix isolation study of the photochemical generation of conjugated ketene, Dewar valence isomer and 1,3-dimethyl-cyclobutadiene

Low temperature IR spectroscopy and photochemistry of matrix-isolated α-pyridil

Photochemical α‐Cleavage in Pyran‐2‐thione: Generation of Aldehyde–Thioketene and Thioaldehyde–Ketene Photoproducts

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