Steric Effects in Displacement Reactions. XI. The Heats of Reaction of Diborane with Pyridine Bases. Steric Strains in Homomorphs of o-t-Butyltoluene and Hemimellitene1

1956 ◽  
Vol 78 (20) ◽  
pp. 5384-5386 ◽  
Author(s):  
Herbert C. Brown ◽  
Lionel Domash
Keyword(s):  
Steric Effects ◽  
Pyridine Bases ◽  
Heats Of Reaction ◽  
Displacement Reactions

Displacement reactions. XIX. Rates and heats of reaction of nucleophiles with .beta.-propiolactone

1969 ◽  
Vol 91 (1) ◽  
pp. 104-107 ◽  
Author(s):  
Robert Earl Davis ◽  
Lydia A. Suba ◽  
Pat Klimishin ◽  
Janet Carter
Keyword(s):  
Heats Of Reaction ◽  
Displacement Reactions

Steric activation in prototropic reactions of pyrazine derivatives. II. The Brønsted relation

1986 ◽  
Vol 64 (6) ◽  
pp. 1090-1092 ◽  
Author(s):  
K. Nagarajan ◽  
T. W. S. Lee ◽  
R. R. Perkins ◽  
Ross Stewart
Keyword(s):  
Transition State ◽  
The Other ◽  
Steric Effects ◽  
Methyl Groups ◽  
Reaction Centre ◽  
Organic Electrolytes ◽  
Methyl Group ◽  
Pyridine Bases ◽  
Tentative Explanation ◽  
High Concentrations

The rate of deprotonation of the 2-methyl group in 1,2,3-trimethylpyrazinium ion by carboxylate, aniline, and pyridine bases has been measured in D2O. Carboxylate ions containing bulky groups near the reaction centre, e.g. ortho benzoates, react faster than predicted by the Brønsted equation that correlates the reactions of unhindered carboxylates. Anilines and pyridines, on the other hand, show conventional steric effects. A tentative explanation for the activation engendered by groups adjacent to the carboxylate centre is based on the known effect that high concentrations of organic electrolytes have on the strengths of carboxylic acids but not of amines. Since ortho carboxylate ions have their relative basicities increased by an alkyl-rich environment, it is argued that the reactive methyl groups of the substrate might provide such an interaction in the transition state.

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