Electrophilic bromination of aromatic conjugated olefins. II. Mechanism of the dual-path additions in stilbene bromination. Evidence from multiple substituent effects for carbonium ion intermediates

1973 ◽  
Vol 38 (3) ◽  
pp. 493-499 ◽  
Author(s):  
Jacques Emile Dubois ◽  
Marie Francoise Ruasse
Keyword(s):  
Substituent Effects ◽  
Carbonium Ion ◽  
Electrophilic Bromination

The Thermal Decomposition of N-Arylcarbamates of t-Alcohols. 2. Effects of Solvent, Temperature, and Substituents

1972 ◽  
Vol 50 (21) ◽  
pp. 3478-3487 ◽  
Author(s):  
S. J. Ashcroft ◽  
Melanie P. Thorne
Keyword(s):  
Diphenyl Ether ◽  
Substituent Effects ◽  
Reaction Rates ◽  
Specific Rate ◽  
Cyclic Transition ◽  
Tertiary Alcohols ◽  
Carbonium Ion ◽  
Tertiary Carbon ◽  
Cyclic Transition State ◽  
Influence Of Solvent

The influence of solvent, ring substituents, and tertiary carbon atom substituents on the decomposition at 423–473 K of some N-arylcarbamates of tertiary alcohols (p-XC6H4NHCO2C(CH3)2R, where X = CH3, H, Cl, NO2, R=C≡CH, C2H5, CH=CH2) has been investigated. In dodecane, diphenyl ether, acetophenone, nitrobenzene, and decanol, the reactions were first order yielding chiefly carbon dioxide, amine, and olefin. t-Pentyl carbamates yielded the olefins 2-methyl-1-butene and 2-methyl-2-butene in a 3:1 mixture. Solvent effects are reflected in variations in enthalpies and entropies of activation, but effects on the actual values of the specific rate constants are small. Substituent effects are also small, with changes in R from C≡CH to CH=CH2 producing only a tenfold rate increase. Variations in X yield Hammett σρ plots with slopes of about 0.50. These results are consistent with the charge separated cyclic transition state proposed before (1). In ethylene glycol, increased reaction rates and 1:1 yields of the olefins from the t-pentyl carbamates indicate a mechanism with greater carbonium ion character.

scholarly journals Substituent Effects in the Benzofuran System. II. Electrophilic Bromination

1974 ◽  
Vol 47 (5) ◽  
pp. 1267-1270 ◽  
Author(s):  
Tadashi Okuyama ◽  
Kiyomitsu Kunugiza ◽  
Takayuki Fueno
Keyword(s):  
Substituent Effects ◽  
Electrophilic Bromination

Gas phase basicities of fluorocarbonyl compounds. An ion cyclotron resonance investigation of the effects of fluorine and trifluoromethyl substituents on hydroxy carbonium ion stabilities

1981 ◽  
Vol 59 (18) ◽  
pp. 2689-2694 ◽  
Author(s):  
C. E. Doiron ◽  
T. B. McMahon
Keyword(s):  
Gas Phase ◽  
Carbonyl Compounds ◽  
Cyclotron Resonance ◽  
Substituent Effects ◽  
Ion Cyclotron Resonance ◽  
Proton Affinities ◽  
Resonance Investigation ◽  
Carbonium Ion ◽  
Hydrogen Bonding Interactions ◽  
Gas Phase Basicities

Gas phase proton affinities for a number of fluoro- and trifluoromethyl-substituted carbonyl compounds have been obtained using a combination of proton transfer equilibria and bracketing experiments. Absolute and relative substituent effects for F and CF3 on carbonyl basicities are determined and discussed in terms of inductive, resonance, polarization, and hydrogen bonding interactions. The data are used to interpolate basicities for HCOF and CF3CHO and are compared to theoretical ab initio calculations.

ChemInform Abstract: SUBSTITUENT EFFECTS IN THE BENZOFURAN SYSTEM PART 2, ELECTROPHILIC BROMINATION

1974 ◽  
Vol 5 (30) ◽  
pp. no-no
Author(s):  
TADASHI OKUYAMA ◽  
KIYOMITSU KUNUGIZA ◽  
TAKAYUKI FUENO
Keyword(s):  
Substituent Effects ◽  
System Part ◽  
Electrophilic Bromination

Quantitative investigation of the ozonolysis reaction. XIV. A simple carbonium ion stabilization approach to the ozone cleavage of unsymmetrical olefins

1970 ◽  
Vol 48 (19) ◽  
pp. 3002-3018 ◽  
Author(s):  
Sándor Fliszár ◽  
Jean Renard
Keyword(s):  
Transition States ◽  
Substituent Effects ◽  
Reaction Paths ◽  
Quantitative Investigation ◽  
Carbonium Ion ◽  
Inductive Effects ◽  
In Trans

The direction of ozone cleavage of selected unsymmetrical olefins R1R2C=CR3R4 to give (a) R1R2CO + R3R4C+OO− and (b) R1R2C+OO− + R3R4CO has been measured, with particular emphasis on the mode of participation of alkyl substituents in distributing the reaction paths a and b. The interpretation, in terms of substituent effects in stabilizing potential zwitterionic carbo-cations in the transition states corresponding to paths a and b, considers (i) the "hyperconjugative stabilization" of positive sites, where the stabilizing abilities of the substituents are in the order CH3 > C2H5 > i-C3H7 > tert-C4H9, and (ii) the participation of inductive effects. The latter appear to be particularly important when the substituents on the two C atoms of the primary ozonide act in the same direction in favoring its electrocyclic cleavage. In the ozonolysis of monosubstituted ethylenes the inductive effects are predominant, i.e. the R—C+HOO− formation is favored by the R groups in the order tert-C4H9 > i-C3H7 > C2H5 > CH3, whereas in trans- and cis-1,2-disubstituted ethylenes "hyperconjugation" governs the direction of cleavage. The cleavage of selected 1,1-disubstituted, tri-, and tetrasubstituted ethylenes is also studied.

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>

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