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

Theoretical insight into the substituent effects on the antioxidant properties of 8-hydroxyquinoline derivatives in gas phase and in polar solvents

2018 ◽  
Vol 96 (5) ◽  
pp. 453-458
Author(s):  
Anes El-Hadj Saïd ◽  
Sidi Mohamed Mekelleche ◽  
Taki-Eddine Ahmed Ardjani
Keyword(s):  
Electron Transfer ◽  
Gas Phase ◽  
Antioxidant Properties ◽  
Substituent Effects ◽  
Hydrogen Atom Transfer ◽  
Polar Solvents ◽  
Antioxidant Power ◽  
Theoretical Insight ◽  
Insight Into

The objective of this work is to perform a theoretical analysis of the antioxidant properties of a series of 8-hydroxyquinolines (8-HQs) to rationalize the available experimental results and to design new potent 8-HQ derivatives. The study was carried out in gas phase and in methanol at the DFT/B3LYP/ 6-311++G(d,p) computational level. The formation of stable ArO• radicals is discussed on the basis of different mechanisms, namely, hydrogen atom transfer (HAT), single electron transfer followed by proton transfer (SET-PT), and single proton loss electron transfer (SPLET). The obtained results show that the HAT mechanism is, thermodynamically, more favoured in gas phase, whereas the SPLET pathway is more favoured in polar solvents. The calculated thermochemical descriptors allow classification of the antioxidant power of the studied compounds.

Photochemical Hydroxylation of Salicylic Acid with Hydrogen Peroxide; Mechanistic Study of Substrate Sensitized Reaction

1996 ◽  
Vol 61 (12) ◽  
pp. 1729-1737 ◽  
Author(s):  
Kamil Lang ◽  
Jiřina Brodilová ◽  
Stanislav Luňák
Keyword(s):  
Hydrogen Peroxide ◽  
Salicylic Acid ◽  
Quantum Yields ◽  
Mechanistic Study ◽  
Isomer Ratio ◽  
Dihydroxybenzoic Acid ◽  
Effect Of Ph ◽  
Product Ratio

The photochemical hydroxylation of salicylic acid (SA) by hydrogen peroxide proceeds via the same intermediate independently of the excited reactant (i.e. SA or H2O2). This conclusion is supported by the similar effect of pH on the quantum yields and on the isomer ratio of formed products: 2,3-dihydroxybenzoic acid (2,3-DHB) and 2,5-dihydroxybenzoic acid (2,5-DHB). The product ratio ([2,3-DHB]/[2,5-DHB]) is not affected by H2O2 concentration.

scholarly journals The origin of the solvent dependence of fluorescence quantum yields in dipolar merocyanine dyes

2019 ◽  
Vol 10 (48) ◽  
pp. 11013-11022 ◽  
Author(s):  
Joscha Hoche ◽  
Alexander Schulz ◽  
Lysanne Monika Dietrich ◽  
Alexander Humeniuk ◽  
Matthias Stolte ◽  
...  
Keyword(s):  
Activation Energy ◽  
Energy Barrier ◽  
Conical Intersection ◽  
Quantum Yields ◽  
Fluorescence Lifetimes ◽  
Activation Energy Barrier ◽  
Polar Solvents ◽  
Fluorescence Quantum Yields ◽  
Solvent Dependence ◽  
Merocyanine Dyes

An increasing activation energy barrier to a conical intersection was identified as the reason for higher fluorescence lifetimes and quantum yields for merocyanines in polar solvents.

Singlet Mechanism for Trans → Cis Photoisomerization of Quaternary Salts of 4-Substituted 4′-Azastilbenes (R = CN, H, CH3, and OCH3) and their Quinolinium Analogues. VIII

1985 ◽  
Vol 40 (5) ◽  
pp. 525-537 ◽  
Author(s):  
H. Görner ◽  
A. Fojtik ◽  
J. Wróblewski ◽  
L. J. Currell
Keyword(s):  
Triplet State ◽  
Low Temperatures ◽  
Room Temperature ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Ion Pairs ◽  
Laser Flash ◽  
Quantum Yields ◽  
Polar Solvents ◽  
Effects Of Temperature

The trans → cis photoisomerization of a series of substituted stilbazolium salts (At+X− , At+: trans-1-alkyl-4-[4-R-styryl]-pyridinium and -quinolinium, R = CN. H, CH3 and OCH3, X− = I and ClO4−) was studied by laser flash photolysis and steady state irradiation measurements. The quantum yields of cis ⇄ trans photoisomerization (ϕc → t and ϕt → c ) and of fluorescence of the trans isomers (ϕf) were determined in several solvents at room temperature and at low temperatures in mixtures of either 2-methyltetrahydrofuran-dichloromethane or ethanolmethanol (E-M). In polar solvents at room temperature ϕt → c is substantial ( ≧ 0.3) and ϕf is small (10−3-10−2). Competition of fluorescence and an activated step in the trans → cis pathway is indicated by the effects of temperature on ϕf and ϕt → c (activation energy: 2 - 3 kcal/mol). A transient, observed only at low temperatures (lifetime τT > 0.5 ms in E-M below -170°C), is assigned to the lowest triplet state with trans configuration. On the basis of the effects of temperature on ϕf, ϕt → c , and the triplet yield and those of quenchers on ϕf and ϕt → c , involvement of the triplet state in the twisting process at room temperature is excluded. Therefore, a singlet mechanism is suggested for the trans → cis photoisomerization of the stilbazolium salts examined. Significant reduction of ϕt → c for iodides in solvents of moderate polarity, where ion pairs are present, is accounted for by photoinduced electron transfer in competition to trans → cis photoisomerization.

Substituent Effects on the Luminescence of 2-Substituted 3-Methylquinoxalines in Poly (Vinyl Alcohol) Films*

1991 ◽  
Vol 46 (4) ◽  
pp. 304-306 ◽  
Author(s):  
Z. Gryczyński ◽  
A. Kawski
Keyword(s):  
Polyvinyl Alcohol ◽  
Temperature Dependence ◽  
Vinyl Alcohol ◽  
Substituent Effects ◽  
Quantum Yields ◽  
Poly Vinyl Alcohol ◽  
Band Position ◽  
Fluorescence And Phosphorescence ◽  
Polyvinyl Alcohol Films

Abstract The effect of 2-substitutions (NH2 . O, CH3O, CI. Br) in 3-methylquinoxalines on the fluorescence and phosphorescence band position and intensity at 293 K, and the temperature dependence of their fluorescence and phosphorescence quantum yields were investigated in polyvinyl alcohol) films

The Determination of Substituent Effects by 13C Nuclear Magnetic Resonance Spectrometry. The Effect of Solvent on CH2X Groups

1985 ◽  
Vol 38 (2) ◽  
pp. 337
Author(s):  
DAR Happer ◽  
BE Steenson
Keyword(s):  
Inductive Effect ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Side Chain ◽  
Polar Solvents ◽  
13C Nuclear Magnetic Resonance ◽  
Nuclear Magnetic Resonance Spectrometry ◽  
Magnetic Resonance Spectrometry ◽  
Lines Of Force

A previous study of the effect of meta- and para-CH2X substituents on the 13C n.m.r. chemical shifts of the α and β side-chain carbons of β- methoxycarbonylstyrenes (methyl cinnamates ) in ethanol has been extended to cover five additional solvents (Me2SO, Me2CO, CDCl3, CCl4 and C6H6). The results support the earlier claim that, for most substituents , the magnitudes of the substituent -induced shifts are proportional to the inductive effect of X. The major contributor to the latter appears to be the field effect generated by the C-X dipole, with the lines of force passing mainly through the molecule. In non-polar solvents, however, there is evidence that lines of force passing directly through the solvent can also influence the shifts in both the meta and para series.

Substituenteneffekte im spektroskopischen Verhalten von Maleinsäurederivaten und 4-Cyclopenten-1.3-dionen / Substituent Effects on the Spectroscopic Behavior of Maleic Acid Derivatives and 4-Cyclopentene-1,3-diones

1973 ◽  
Vol 28 (9-10) ◽  
pp. 662-681 ◽  
Author(s):  
Hans-Dieter Scharf ◽  
Hans Leismann
Keyword(s):  
Excited States ◽  
Maleic Acid ◽  
Singlet State ◽  
Substituent Effects ◽  
Quantum Yields ◽  
Mo Calculations ◽  
Excited Singlet ◽  
Inductive Effects ◽  
Phosphorescence Emission ◽  
Spectroscopic Behavior

The lowest excited states of maleic acid- and cyclopentendionderivatives have been investigated by UV-absorption and phosphorescence emission spectroscopy. While the first excited singlet-state S1 is of 1(nπ*)-type in all compounds, the lowest triplet-state T1 was found to be a mixture of 3(nπ*) and 3(ππ*)-configurations. For the emitting derivatives (Ζ ≠ Η) phosphorescence-lifetimes and -quantum yields as well as the probability for intersystem crossing have been determined.Considering the inductive effects of all substituents on the S1 (nπ*) -energy, Coulombpotentials for sulfur and iodine in terms of Huckel-parameters: hs = 0,2 and hj = —0,5 have been derived.The results of Hückel-MO-calculations can be correlated to the measured values of all compounds with the exception of the iodine containing derivatives.

Additivity of substituent effects on the proton–proton coupling constants in substituted benzenes. Investigation of some trisubstituted benzenes

1968 ◽  
Vol 46 (15) ◽  
pp. 2531-2534 ◽  
Author(s):  
T. Schaefer ◽  
G. Kotowycz ◽  
H. M. Hutton ◽  
J. W. S. Lee
Keyword(s):  
Root Mean Square ◽  
Substituent Effects ◽  
Coupling Constants ◽  
Mean Square ◽  
Polar Solvents ◽  
Substituted Benzenes ◽  
Proton Proton ◽  
Temperature Range ◽  
Proton Coupling ◽  
Saturation Effects

An additivity scheme based on the changes in ortho, meta, and para proton coupling constants of benzene induced by a single substituent is applied to a number of trisubstituted benzenes. Ortho coupling constants are well reproduced (root mean square deviations = 0.05 c.p.s.) by the scheme but for meta and para couplings saturation effects are indicated. For the latter two couplings there are two substituents ortho to one of the protons involved. Measurements indicate that a temperature range of 100 °C has a negligible effect on the couplings but that polar solvents are to be avoided in obtaining data for the testing of additivity schemes.

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