Cyclohexadienyl cations. IV. Methoxy substituent effects in the dienone-phenol rearrangement

1972 ◽  
Vol 37 (21) ◽  
pp. 3339-3342 ◽  
Author(s):  
V. P. Vitullo ◽  
Elizabeth A. Logue
Keyword(s):  
Substituent Effects ◽  
Methoxy Substituent

scholarly journals Substituent effects on the spectral behavior and synthesis of mercury 1,5-diarylthiocarbazonates

1981 ◽  
Vol 59 (4) ◽  
pp. 679-687 ◽  
Author(s):  
Nori Y. C. Chu ◽  
Steven A. Goldstein ◽  
Philip M. Keehn
Keyword(s):  
Bathochromic Shift ◽  
Substituent Effects ◽  
Spectral Shift ◽  
Spectral Studies ◽  
Hypsochromic Shift ◽  
Electronic Effects ◽  
Activated State ◽  
Mercury Complexes ◽  
Inductive Effects ◽  
Methoxy Substituent

Symmetric and unsymmetric substituted 1,5-diarylthiocarbazones, and their mono- and bismercury complexes, were synthesized for spectral analysis. The first singlet–singlet transition of the mercury complexes was determined and the spectral shift produced by trifluoromethyl substitution was compared with that caused by different substituents in similar complexes. The large magnitude of the hypsochromic shift produced by the trifluoromethyl substituent can be explained by concerted steric and inductive effects, while the smaller bathochromic shift induced by the methoxy substituent is a result of opposing steric and electronic effects. In the trifluoromethyl substitution, a hypsochromic shift caused by steric influences was found to be 500 cm−1 in the photochromic unactivated state, and 250 cm−1 in the photochromic activated state. A similar shift caused by inductive influences was found to be 750 cm−1 in the photochromic unactivated state, and 600 cm−1 in the photochromic activated state. The smaller spectral shift observed in the photochromic activated state is consistent with the elucidated structure of the unsymmetric 1,5-diarylthiocarbazone, 6d, which was shown that the trifluoromethyl substitution was on the phenylazo portion of the molecule by chemical and spectral studies.

Theoretical study to evaluate polyfuran electrical conductivity and methylamine, methoxy substituent effects

2008 ◽  
Vol 861 (1-3) ◽  
pp. 137-141 ◽  
Author(s):  
Ricardo Vivas-Reyes ◽  
Luz Dary Mercado ◽  
Jorge Anaya-Gil ◽  
Andrés G. Marrugo ◽  
Emiliano Martinez
Keyword(s):  
Electrical Conductivity ◽  
Theoretical Study ◽  
Substituent Effects ◽  
Methoxy Substituent

Ortho substituent effects on transfer of aryl groups from oxygen to carbon in adducts from diaryloxycarbenes and DMAD

2002 ◽  
Vol 80 (3) ◽  
pp. 228-234 ◽  
Author(s):  
Xiaosong Lu ◽  
John Warkentin
Keyword(s):  
Cyano Group ◽  
Substituent Effects ◽  
Aromatic Substitution ◽  
Aryl Group ◽  
Electron Pairs ◽  
Work Support ◽  
Ipso Substitution ◽  
Positive Site ◽  
Methoxy Substituent ◽  
Ortho Substituent

Diaryloxycarbenes, generated by thermolysis of 2,2-diaryloxy-5,5-dimethyl-Δ3-1,3,4-oxadiazolines in benzene, reacted with dimethyl acetylenedicarboxylate (DMAD) to afford triesters. The triesters arose by aryl-group transfer from oxygen to carbon (ipso substitution). A cyano group in the para position had been shown earlier to favour the ipso substitution whereas a para-methoxy group disfavoured it. Surprisingly, the ortho-methoxy substituent also favoured ipso substitution. As a tentative rationale, we had proposed that a vinylogous diaryloxycarbene intermediate, with dipolar properties, is formed when a diaryloxycarbene attacks at the sp-carbon of DMAD and that an ortho substituent, with one or more unshared electron pairs, can stabilize the intermediate by donating electron density to the positive site. In the present work, support for that interpretation and for the importance of a steric effect, was provided by examining the competition between (i) p-tolyl and phenyl; (ii) o-tolyl and phenyl; (iii) o-iodophenyl and phenyl; (iv) o-iodophenyl and p-chlorophenyl; and (v) o-bromophenyl and p-chlorophenyl as potential migrating groups.Key words: aromatic substitution, carbene, ipso, diaryloxycarbene, oxadiazoline.

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.

Ketonization of (Z)-2-methoxy-1,2-diphenylvinyl alcohol. Quantitative evaluation of the remarkable kinetic stability of this enol

1998 ◽  
Vol 76 (9) ◽  
pp. 1284-1288
Author(s):  
E A Jefferson ◽  
A J Kresge ◽  
L Matthew ◽  
Z Wu
Keyword(s):  
Methoxy Group ◽  
Substituent Effects ◽  
Phenyl Group ◽  
Hydrogen Ion ◽  
Ammonium Ion ◽  
Enhancing Effect ◽  
Global Rate ◽  
Methoxy Substituent ◽  
Aqueous Perchloric Acid ◽  
Rate Profile

Rates of ketonization of (Z)-2-methoxy-1,2-diphenylvinyl alcohol were measured in aqueous perchloric acid and sodium hydroxide solutions as well as in formic acid and ammonium ion buffers, and the results were used to construct a rate profile for this reaction. These data show this substance to be a remarkably stable enol with a lifetime of 3.6 h at the bottom of its rate profile and a hydrogen ion catalytic coefficient 660 000 times less than that for the enol of acetophenone. Comparison with simple models allows partition of this rate factor into a 440-fold retardation for the β-phenyl substituent and a 1500-fold retardation for the β-methoxy substituent. A global rate of enolization of the keto isomer producing both Z and E enol isomers was also measured, and this leads to pKE > 5.4 as the lower limit of the keto-enol equilibrium constant for the Z enol. This result could be dissected into an enol-content enhancing effect of δ pKE = 3.2 for the β-phenyl group and a surprising enol-content diminishing effect of δ pKE > 0.6 for the β-methoxy group. Key words: enol ketonization, enol stability, keto-enol equilibrium, β-phenyl and β-methoxy substituent effects in keto-enol systems.

Substituent effects and solvents

1992 ◽  
Vol 89 ◽  
pp. 1567-1571
Author(s):  
O Pytela ◽  
M Ludwig
Keyword(s):  
Substituent Effects

Substituent Effects on the Thermal Decomposition of Phosphate Esters on Ferrous Surfaces

2019 ◽  
Author(s):  
James Ewen ◽  
Carlos Ayestaran Latorre ◽  
Arash Khajeh ◽  
Joshua Moore ◽  
Joseph Remias ◽  
...  
Keyword(s):  
Thermal Decomposition ◽  
Film Formation ◽  
Substituent Effects ◽  
Vapour Phase ◽  
Industrial Applications ◽  
Phosphate Esters ◽  
Antiwear Additives ◽  
Formation Mechanisms ◽  
Phosphate Ester ◽  
Wide Range

<p>Phosphate esters have a wide range of industrial applications, for example in tribology where they are used as vapour phase lubricants and antiwear additives. To rationally design phosphate esters with improved tribological performance, an atomic-level understanding of their film formation mechanisms is required. One important aspect is the thermal decomposition of phosphate esters on steel surfaces, since this initiates film formation. In this study, ReaxFF molecular dynamics simulations are used to study the thermal decomposition of phosphate esters with different substituents on several ferrous surfaces. On Fe<sub>3</sub>O<sub>4</sub>(001) and α-Fe(110), chemisorption interactions between the phosphate esters and the surfaces occur even at room temperature, and the number of molecule-surface bonds increases as the temperature is increased from 300 to 1000 K. Conversely, on hydroxylated, amorphous Fe<sub>3</sub>O<sub>4</sub>, most of the molecules are physisorbed, even at high temperature. Thermal decomposition rates were much higher on Fe<sub>3</sub>O<sub>4</sub>(001) and particularly α-Fe(110) compared to hydroxylated, amorphous Fe<sub>3</sub>O<sub>4</sub>. This suggests that water passivates ferrous surfaces and inhibits phosphate ester chemisorption, decomposition, and ultimately film formation. On Fe<sub>3</sub>O<sub>4</sub>(001), thermal decomposition proceeds mainly through C-O cleavage (to form surface alkyl and aryl groups) and C-H cleavage (to form surface hydroxyls). The onset temperature for C-O cleavage on Fe<sub>3</sub>O<sub>4</sub>(001) increases in the order: tertiary alkyl < secondary alkyl < primary linear alkyl ≈ primary branched alkyl < aryl. This order is in agreement with experimental observations for the thermal stability of antiwear additives with similar substituents. The results highlight surface and substituent effects on the thermal decomposition of phosphate esters which should be helpful for the design of new molecules with improved performance.</p>

Sign in / Sign up

Export Citation Format

Share Document