Substituent effects in aromatic photochemistry. UV irradiation of 3,4-dimethoxybenzonitrile and 3,4-dimethoxyacetophenone in the presence of inorganic anions

1987 ◽  
Vol 52 (4) ◽  
pp. 980-988 ◽  
Author(s):  
Petr Kuzmič ◽  
Milan Souček
Keyword(s):  
Substituent Effects ◽  
Quantum Yields ◽  
Substituted Benzenes ◽  
Cyanide Anion ◽  
Nucleophilic Displacement ◽  
Relative Quantum ◽  
Ultraviolet Photolysis ◽  
Substitution Ratio ◽  
Volmer Plot ◽  
Methoxy Substituent

Ultraviolet photolysis of 3,4-dimethoxybenzonitrile (Ia) and 3,4-dimethoxyacetophenone (IIa) in the presence of the hydroxide or cyanide anion leads to nucleophilic displacement of either the para or the meta methoxy substituent. The ratio of isomeric photoproducts is dependent upon the nature of the nucleophile. Photoreactions with the OH- anion lead exclusively to the substitution at C-3. On the other hand, both isomers are formed when acetophenone IIa is irradiated in the presence of CN-, with the C-3/C-4 substitution ratio 3:2. In the case of the photocyanation of Ia, the C-4 substituted product dominates, the C-3/C-4 ratio ranging from 1:2 to 1:6 in dependence on the nucleophile concentration. These differences between the OH- and CN- anions are related to the results of a fluorescence quenching study which has revealed that only the latter nucleophile interacts with singlet-excited substrates. A non-linear Stern-Volmer plot was observed for the quenching of the second excited state of Ia by the cyanide anion. This indicates several distinct quenching modes, in relation to the concentration dependence of regioselectivity. The activating power of –H, -CN, -COCH3, and -NO2 substituents, as measured by relative quantum yields of disappearance for 3,4-dimethoxy-R-substituted benzenes, is 1:2.5:5:580 and 1:1.5:6:1000 in their photoreactions with OH- and CN- anions, respectively.

Electronic spectroscopy of the transition of DCO and lifetimes and relative quantum yields of the state

2011 ◽  
Vol 270 (1) ◽  
pp. 33-39 ◽  
Author(s):  
Steven J. Rowling ◽  
Scott A. Reid ◽  
Klaas Nauta ◽  
Scott H. Kable
Keyword(s):  
Electronic Spectroscopy ◽  
The State ◽  
Quantum Yields ◽  
Relative Quantum

Solvent and substituent effects on rearrangement of 4-(4-X-phenyl)-2,7-dioxa-3-azabicyclo[3,3,0]oct-3-enes

1985 ◽  
Vol 50 (9) ◽  
pp. 1971-1981 ◽  
Author(s):  
Lubor Fišera ◽  
Marta Konopíková ◽  
Ladislav Štibrányi ◽  
Hans-Joachim Timpe
Keyword(s):  
Substituent Effects ◽  
Quantum Yields ◽  
Polar Solvents ◽  
Aromatic Residue ◽  
Product Ratio ◽  
Oxazoline Derivatives ◽  
Oxazine Derivatives

Preparation of the title compounds V is described. They give, on irradiation, the 2,3-dihydro-6H-1,3-oxazine derivatives VI as the main products besides the tetrahydrofuro[3,4-d]oxazoline derivatives VII. The VI to VII product ratio depends on the substituent bound to the aromatic residue. Polar solvents favour formation of the VI derivatives in the order Cl >H > CH3. In non-polar solvents the proportion of VII is increased. The quantum yields of the photoreaction vary within the limits from 0.006 to 0.04 (H >F > Cl > CH3 > OCH3).

scholarly journals SUBSTITUENT EFFECTS ON THE PHOTOCURRENT QUANTUM YIELDS OF PARA-SUBSTITUTED TETRAPHENYLPORPHYRINS

1980 ◽  
Vol 9 (6) ◽  
pp. 627-628 ◽  
Author(s):  
Kazuo Yamashita ◽  
Keiko Miyoshi ◽  
Atsuhiro Osuka ◽  
Hitomi Suzuki
Keyword(s):  
Substituent Effects ◽  
Quantum Yields

The Mechanism of the HgH A22Π3/2 → X2Σ+ Emission in the Hg(63P0) Photosensitization of Hydrogen and the Alkanes

1973 ◽  
Vol 51 (8) ◽  
pp. 1207-1214 ◽  
Author(s):  
A. C. Vikis ◽  
D. J. Le Roy
Keyword(s):  
Ground State ◽  
Quantum Yields ◽  
Primary Process ◽  
Relative Quantum

The mechanism of the HgH A22Π3/2 → X2Σ+ emission detected in the Hg(63P0) photosensitized decomposition of H2 and some of the lower alkanes, RH, was investigated. It was concluded that ground state HgH was formed in the primary process Hg(63P0) + RH(or H2) → HgH(X2Σ+) + R(or H). The HgH A22Π3/2 → X2Σ+ emission and presumably the A12Π1/2 → X2Σ+ and B2Σ+ → X2Σ+ emission, also observed in the above systems, result from secondary excitation of ground state HgH on collision with Hg(63P0). Studies of the emission made possible the estimation of relative quantum yields for the above primary process.

Wavelength controlled production of SO4- radicals in the ultraviolet photolysis of ceric sulfate solutions

1984 ◽  
Vol 37 (3) ◽  
pp. 475 ◽  
Author(s):  
RW Matthews
Keyword(s):  
Rate Constants ◽  
Photochemical Reaction ◽  
Transfer Reaction ◽  
Quantum Yields ◽  
Oh Radical ◽  
Transfer Energy ◽  
Fluorescence Measurements ◽  
Sulfate Solutions ◽  
Ultraviolet Photolysis ◽  
Primary Photochemical Reaction

Solutions of cerium(III)/(IV) and formic acid in 0.4 M sulfuric acid have been photolysed under 254 nm and 365 nm light. Marked differences in the reaction kinetics and quantum yields are observed at the two different wavelengths. At 365 nm, the reactions leading to cerium(IV) reduction are caused almost exclusively by the SO4- radical. The ratio of rate constants, k(SO4- + CeIII)/ k(SO4- + HCOOH), is 116 � 11 and the quantum yield of sulfate radicals, ф(SO4-), is 0.023 � 0.002. At 254 nm, the reactions leading to cerium(IV) reduction are caused mainly by the OH radical, but approximately 35% of the oxidizing radicals formed in the primary photochemical reaction are SO4-. Cerium(III) species, excited at 254 nm, transfer energy to cerium(IV) and this results in an additional yield of OH and SO4- radicals. Fluorescence measurements confirmed the efficiency of the energy transfer reaction. The ratio of rate constants, k(OH+CeIII)/k(OH+HCOOH), is 2.22 � 0.18 and ф(CeIV*) and ф(CelIII*) giving oxidizing radicals are 0.116 � 0.010 and 0.0083 � 0.0008 respectively. Thus about 5 times more total oxidizing radicals are produced from excited cerium(IV) species at 254 nm than at 365 nm.

Fluorescence lifetimes and relative quantum yields of 124-kilodalton oat phytochrome in water and deuterium oxide solutions

Biochemistry ◽  
1987 ◽  
Vol 26 (5) ◽  
pp. 1412-1417 ◽  
Author(s):  
Helmut Brock ◽  
Bela P. Ruzsicska ◽  
Tatsuo Arai ◽  
Wilhelm Schlamann ◽  
Alfred R. Holzwarth ◽  
...  
Keyword(s):  
Deuterium Oxide ◽  
Quantum Yields ◽  
Fluorescence Lifetimes ◽  
Relative Quantum

The photolysis of ozone by ultraviolet radiation. VI. Reactions of O( 1 D)

1972 ◽  
Vol 330 (1580) ◽  
pp. 131-146 ◽  
Keyword(s):  
Quantum Yield ◽  
Oxygen Carrier ◽  
Quantum Yields ◽  
Ozone Decomposition ◽  
Resonance Fluorescence ◽  
Significant Extent ◽  
Molecular Product ◽  
Relative Quantum ◽  
Carrier Gases ◽  
Made In

Tho reactions of O( 1 D) with O 3 , and with O 2 , have been studied by means of two essentially different techniques. Relative quantum yields for ozone decomposition after photolysis by λ = 254 nm radiation were measured by following changes in optical absorption. Relative concentrations of ground state oxygen atoms were measured by means of a resonance fluorescence technique. In both cases, measurements were made in the presence of O 2 , N 2 or He carrier gases in a flow system, at such time after photolysis that reactions involving O( 1 D) and O 2 ( 1 ∑ g + ) had gone to completion, whereas those involving O( 3 P) and O 2 ( 1 Δ g ) had not proceeded to a significant extent. The ‘intermediate’ quantum yields for ozone photolysis in helium and oxygen are 1.9 and 1.6 respectively, referred to an assumed intermediate quantum yield for photolysis in nitrogen of 1.0. In an oxygen carrier, for every ozone molecule decomposed in the primary step there results 1.5 ± 0.1 O( 3 P) atoms. For photolysis in helium this number is approximately 0.6. The results suggest that there are two pathways for the reaction between O( 1 D) and O 3 , in one of which the products are O 2 + 2O: two O atoms are formed on approximately one-third of reactive collisions. There is no evidence for production of an excited molecular product which is reactive on the concentration-time scale of these experiments. It is shown that both the intermediate quantum yield and the [O ( 3 P)] measurements are consistent with the formation of molecular oxygen in the 1 ∑ g + state on 50 to 60% of quenching collisions between O( 1 D) and O 2 .

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