Substituent effects in anthrasemiquinones. Part 2.—Use of additivity principles and linear correlation plots

1992 ◽  
Vol 88 (23) ◽  
pp. 3423-3429 ◽  
Author(s):  
Jens A. Pedersen
Keyword(s):  
Linear Correlation ◽  
Substituent Effects

scholarly journals Notable Substituent Effects on the Rate Constant of Thermal Denitrogenation of Cyclic Azoalkanes: Strong Evidence for a Stepwise Denitrogenation Mechanism

2010 ◽  
Vol 63 (12) ◽  
pp. 1615 ◽  
Author(s):  
Chizuko Ishihara ◽  
Manabu Abe
Keyword(s):  
Rate Constant ◽  
Linear Correlation ◽  
Strong Evidence ◽  
Bond Cleavage ◽  
Relative Rate ◽  
Substituent Effects ◽  
Relative Rate Constant ◽  
Rate Determining Step ◽  
Singlet Diradicals ◽  
Type Radical

The thermal denitrogenation rates (k) of a series of 7,7-dimethoxy-1,4-diaryl-2,3-diazabicyclo[2.2.1]hept-2-ene derivatives 2 with a variety of aryl groups (p-CNC6H4, C6H5, p-MeC6H4, p-MeOC6H4) were determined to investigate the denitrogenation mechanism. A linear correlation (r = 0.988) between the relative rate-constant (log krel) of the denitrogenation reaction and Arnold’s σα• parameter for benzylic-type radical-stabilization was observed. However, the relative rate-constant was not correlated with the substituent effect on the lifetime of the resulting singlet diradicals DR2. These results indicate that the rate-determining step of denitrogenation of 7,7-dimethoxy-2,3-diazabicyclo[2.2.1]hept-2-ene derivatives involves stepwise C–N bond cleavage.

A linear correlation of aromatic substituent effects with geminal coupling constants

1967 ◽  
Vol 45 (21) ◽  
pp. 2489-2491 ◽  
Author(s):  
Richard W. Franck ◽  
Joseph Auerbach
Keyword(s):  
Linear Correlation ◽  
Substituent Effects ◽  
Coupling Constants ◽  
Asymmetric Center ◽  
Proton Proton ◽  
Aromatic Substituent ◽  
Benzyl Alcohols ◽  
Proton Coupling ◽  
Geminal Coupling ◽  
Hammett Σ Constants

A linear correlation of the geminal coupling constants of benzylic protons with the Hammett σ constants has been observed. The proton–proton coupling was made observable by preparing the tetrahydropyranyl ethers of benzyl alcohols. The introduction of the asymmetric center caused the benzyl protons to become non-equivalent. The observed correlation serves as an additional confirmation of the Pople and Bothner-By theory of geminal coupling.

A Rationale for the Linear Correlation of Aryl Substituent Effects in Iron(0) Tricarbonyl Complexes Containing α,β-Unsaturated Enone (Chalcone) Ligands

2007 ◽  
Vol 26 (25) ◽  
pp. 6354-6365 ◽  
Author(s):  
Benjamin E. Moulton ◽  
Anne K. Duhme-Klair ◽  
Ian J. S. Fairlamb ◽  
Jason M. Lynam ◽  
Adrian C. Whitwood
Keyword(s):  
Linear Correlation ◽  
Substituent Effects ◽  
Aryl Substituent

1H and 13C dynamic nuclear magnetic resonance study of hindered rotation in thiobenzoylpiperidines and thiobenzoylmorpholines. Correlation between barrier heights of amides and thioamides

1977 ◽  
Vol 55 (14) ◽  
pp. 2649-2655 ◽  
Author(s):  
Carla Piccinni-Leopardi ◽  
Omer Fabre ◽  
Daniel Zimmermann ◽  
Jacques Reisse ◽  
F. Cornea ◽  
...  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Linear Correlation ◽  
Substituent Effects ◽  
Nuclear Magnetic Resonance Study ◽  
Free Energies ◽  
Magnetic Resonance Study ◽  
Hindered Rotation ◽  
Barrier Heights ◽  
Dynamic Nuclear Magnetic Resonance

The free energies of activation for hindered rotation around the C—N bond have been determined for a series of N,N-disubstituted thioamides by means of 13C and 1H dynamic nmr.A comparison between barriers for 20 amides and the corresponding thioamides, studied under similar conditions, has been drawn up using both our results and data obtained from the literature. An excellent linear correlation has been obtained. The same correlation also holds for primary (thio)amides and seems to be of general significance. Substituent effects on the barrier heights of thioamides and amides are discussed in connection with some particular cases.

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>

Chemistry of Unsymmetrical C1-Substituted Oxabenzonorbornadienes

2021 ◽  
Vol 17 ◽  
Author(s):  
Austin Pounder ◽  
Angel Ho ◽  
Matthew Macleod ◽  
William Tam
Keyword(s):  
Transition Metal ◽  
Metal Complexes ◽  
Transition Metal Complexes ◽  
Substituent Effects ◽  
Face Selectivity ◽  
Transition Metal Catalyzed ◽  
Catalyzed Reactions ◽  
Metal Catalyzed ◽  
Synthetic Intermediate

: Oxabenzonorbornadiene (OBD) is a useful synthetic intermediate which can be readily activated by transition metal complexes with great face selectivity due to its dual-faced nature and intrinsic angle strain on the alkene. To date, the understanding of transition-metal catalyzed reactions of OBD itself has burgeoned; however, this has not been the case for unsymmetrical OBDs. Throughout the development of these reactions, the nature of C1-substituent has proven to have a profound effect on both the reactivity and selectivity of the outcome of the reaction. Upon substitution, different modes of reactivity arise, contributing to the possibility of multiple stereo-, regio-, and in extreme cases, constitutional isomers which can provide unique means of constructing a variety of synthetically useful cyclic frameworks. To maximize selectivity, an understanding of bridgehead substituent effects is crucial. To that end, this review outlines hitherto reported examples of bridgehead substituent effects on the chemistry of unsymmetrical C1-substituted OBDs.

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