Photolysis of 7,8-digermabicyclo[2.2.2]octadiene. The investigation of the elementary stages by means of 1H CIDNP and laser pulse photolysis (original) (raw)
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Organometallics, 2000
The photochemistry of 1,4-diphenyl-2, 3-benzo-7,7,8,8-tetraalkyl-7,8-digermabicyclo[2.2.2]octadienes in solution has been studied in detail by steady-state, nanosecond laser flash photolysis, and matrix isolation techniques. Photolysis of 7,8-digermabicyclo[2.2.2]octadienes in solution resulted mainly in the formation of tetraalkyldigermenes and 1,4-diphenylnaphthalene in the triplet excited state. The 7,8-digermabicyclo[2.2.2]octadiene also photochemically isomerized to 1,4-diphenyl-2,3-benzo-6,6,7,7-tetraalkyl-6,7-digermatricyclo[3.3.0.0]octane as minor product. The reactions of tetraalkyldigermenes with butadienes (2,3dimethylbuta-1,3-diene and 2-methylbuta-1,3-diene), carbon tetrachloride, and methanol gave the corresponding digermene trapped products: 1,2-digermacyclohex-4-enes, 1,2-dichlorodigermanes together with hexachloroethane, and methoxydigermanes, respectively, in good yields. The transient bands of tetraalkyldigermenes using nanosecond laser flash photolysis appeared at ca. 380 nm. The rate constants for the quenching reactions of the digermene with oxygen, polyhalomethanes, alcohols, 2,3-dimethylbuta-1,3-diene, 1-hexyne, and triethylsilane were also measured under various conditions. The quenching reactions of digermenes with carbon tetrachloride and ethanol (k ) ∼10 7 M -1 s -1 ) are 100 times faster than that with 1,3-butadiene (k ) ∼10 5 M -1 s -1 ). The digermenes were very rapidly quenched with oxygen (k ) ∼10 8 M -1 s -l ), but very slowly with 1-hexyne and triethylsilane (k < 10 4 M -1 s -l ) under reaction conditions. The UV absorption bands of tetraalkyldigermenes generated from 7,8-digermabicyclo[2.2.2]octadienes in matrix at 77 K were also observed at 370-380 nm. The mechanism of digermene formation was also discussed.
Journal of the American Chemical Society, 1971
Mechanistic studies on the photorearrangements of benzobicyclo[2.2.2]octadienone (1) and bicyclo-[2.2.2]octenone (5) are reported. The limiting quantum yields for the singlet reaction of 1 are: &is = 0.50; @nsphthslene = 0.45; ~4,5-benLobie,c~o[l.l.0100ta-2,1-dion.8~0~~ = 0.10. The limiting quantum yields for the acetophenonesensitized reaction are: adis = 0.14; anaphthslene = 0.01 ; ~b e n r o t r i o y e l o [ 3 . 3 . 0 , 0 2~8~~~t e n~3 . 0 n e = 0.12. A deuterium labeling experiment established the 1,2-acyl migration mechanism for the photosensitized rearrangement of 1. Finally, it was shown that the triplet reaction proceeded by a concerted, symmetry-allowed process by comparison with the photoisomerization of lactone 12.
Fast Processes and Intermediates in Photochemistry of 7-Dimethyl-germanorbornadiene
The Journal of Physical Chemistry A, 2006
Laser pulse photolysis experiments have shown that the triplet excited-state of 1,2,3,4-tetraphenylnaphthalene (TPN) is one of the primary intermediates of the photochemical transformation of 7,7′-dimethylgerma-1,4,5,6tetraphenyl-2,3-benzo-norbornadiene (GNB) in hexane solution. The molar absorption of T-T absorption and the quantum yield of the intersystem crossing of TPN were determined from the triplet-triplet energy transfer. The scheme of GNB photocleavage has been suggested where the triplet excited TPN originated from the triplet state of biradical through cleavage of the second C-Ge bond, the latter being generated from the excited singlet state of the initial GNB after the cleavage of the first C-Ge bond and the intersystem crossing. Other channels of GNB's chemical transformation have been discussed.
Re-examination of the photochemical reaction of octaisopropylcyclotetragermane
Journal of Organometallic Chemistry, 2007
The photochemistry of octaisopropylcyclotetragermane was studied by laser flash photolysis and trapping experiments. Upon irradiation of the cyclotetragermane, the main reaction was a ring opening to form octaisopropyltetragermane-1,4-diyl biradical (k max = 310 and 550 nm), but generations of diisopropylgermylene and tetraisopropyldigermene are negligible.
Photochemistry of 1-(2,6-dichlorobenzyl)-1,4-dihydronicotinamide
Tetrahedron Letters, 1985
1,4,5,6-tetrahydropyridines Via and VIb were obtained. The investigation on the photochemistry of NADH and model compounds is centered around the electron-transfer processes and the reducing properties of these substances.' Few works are devoted to the photocycloadditions of 1,4-dihydropyridines which take place in nonoxidizing conditions, with high regio-and stereo-specificity: 1,4-dihydropyridine-3,5-dicarboxylate dimerizes giving head-to-tail-= and head-to-tail-anti dimers,2 1-benzyl-1,4-dihydronicotinamide (BNAH) give head-to-tail--dimer 3 or, in the presence of acrylonitrile, photoadducts across the 2-3 double bond. 4
2014
The synthesis of the first member of a new class of Dewar benzenes has been achieved. The synthesis of 2,3- dimethylbicyclo[2.2.0]hexa-2,5-diene-1, 4-dicarboxylic acid and its anhydride are described. Dibromomaleic anhydride and dichloroethylene were found to add efficiently in a photochemical [2+2] cycloaddition to produce 1,2-dibromo- 3,4-dichlorocyclobutane-1,2-dicarboxylic acid. Removal of the bromines with tin/copper couple yielded dichloro- cyclobutenes which added to 2-butyne under photochemical conditions to yield 5,6-dichloro-2,3-dimethylbicyclo [2.2.0] hex-2-ene dicarboxylic acids. One of the three possible isomers yielded a stable anhydride which could be dechlorinated using triphenyltin radicals generated by the photolysis of hexaphenylditin. Photolysis of argon matrix isolated 2,3-dimethylbicyclo [2.2.0]hexa-2, 5-diene-1,4-dicarboxylic acid anhydride produced traces whose strongest bands in the infrared were at 3350 and 600 cm^(-1). This suggested the formation of termi...
Journal of Organic Chemistry, 1985
The thermolysis and 350-nm and 185-nm photolyses of the azoalkanes 2,3-diazabicyclo[2.2.l]hept-2-ene (la) and spiro[cyclopropane-1,7'-[2,3]diazabicyclo[2.2.l]hept-2-ene] (lb) have been investigated. The exo/endo stereochemistry in the bicyclo[2.l.Q]pentanes 2a,b and in the rearranged olefin 3b w a~ determined by deuteration experiments using 5,6-exo-dideuterioazoalkanes la,b-d2. Whereas thermal and direct photochemical (350 nm; n, T * ) denitrogenation of azoalkane la-d2 led exclusively (>99%) to bicyclo[2.1.0]pentane 2a-dz with preferential (1.54, 2.94) double inversion, the triplet-sensitized photolysis afforded nearly complete stereoequilibration. In 185-nm denitrogenation an unexpectedly high exo/endo ratio (3.1) for bicyclo[2.1.O]pentane 2a-d, was found, besides isomerization to cyclopentene 2a-dz. Similar results were obtained in the denitrogenation of spiroazoalkane lb-d2, which exhibited exo stereochemical preferences in both photoproducts spiro[bicyclo[2.1.0]pentane-5,1'cyclopropane] 2b-d2 and bicyclo[3.2.0]hept-l-ene 3b-d2. The 350-nm photolysis of azoalkane lb-d, gave preferential formation of ezo-spirobicyclo[2.1.O]pentane 2b-d2 and exo-olefin 3b-d2, whereas triplet-sensitized decomposition yielded almost complete loss of stereochemical preference in the olefin 3b-dz. The 185-nm photolysis of azoalkane lb-d2 showed similar behavior compared with the azoalkane la, e.g., a t high exo/endo ratio in spirobicyclo-[Z.l.O]pentane 2b-d2. Also olefin 3b was formed with complete stereoequilibration. These diverse experimental results are discussed in terms of one-bond vs. two-bond cleavage processes leading to the diazenyl diradicals D'n,,,
The photolysis of 2,4,5,6-tetrachloro-1,3,-dicyanobenzene
Journal of Photochemistry and Photobiology A: Chemistry, 1989
undergoes extensive transformation to many photoproducts of single and sequential excitation on UV irradiation in ethanol. Cl *H and CN + H exchange take place with the solvent, and solvent incorporation occurs followed by cyclization on the cyano group(s) and/or further side-chain deoxygenation. Cl + Et exchange is also observed. The photoproducts were identified by gas chromatographymass spectrometry (GC-MS). Some were isolated and analysed by IR and nuclear magnetic resonance (NMR) spectroscopy, which provided evidence for their structural identification. o-Chlorobenzonitrile was found to yield only the product of photoreduction of the C-Cl bond.
Photochemistry of bridged cycloheptadienones
Tetrahedron, 1974
A series of 6,7-Benzobicyclol3.2.l]octadienes (10-13) have been prepared. Direct and sensitized irradiation of the dienes gave di-m-methane rearrangement products (M-17). Quantum yields for the direct and sensitized rearrangements were recorded and compared. Substituent effect and structure-multiplicity relationships are discussed.