Steric Effects in Displacement Reactions. IX. Steric Strains in the Reactions of 2,6-Lutidine and 2,4,6-Collidine with Methyl Iodide and with Boron Trifluoride1

1956 ◽  
Vol 78 (20) ◽  
pp. 5375-5377 ◽  
Author(s):  
Herbert C. Brown ◽  
Daniel Gintis ◽  
Harold Podall
Keyword(s):  
Methyl Iodide ◽  
Steric Effects ◽  
Displacement Reactions

Acidity measurements in THF. III. Aldimines and ketimines

1983 ◽  
Vol 61 (12) ◽  
pp. 2729-2734 ◽  
Author(s):  
Robert R. Fraser ◽  
Monique Bresse ◽  
Noemi Chuaqui-Offermanns ◽  
K. N. Houk ◽  
N. G. Rondan
Keyword(s):  
Nmr Spectroscopy ◽  
Methyl Iodide ◽  
Quantitative Estimation ◽  
Steric Effects ◽  
Alkyl Substitution ◽  
C Nmr ◽  
Abinitio Calculations

The relative acidities of fiteen aldimines and ketimines have been measured in THF using either 13C nmr spectroscopy or trapping experiments with methyl iodide. The pKA's are found to vary over a range of more than four pK units. The effects of structure on acidity indicate the acid-weakening effect of alkyl substitution in ketimines to be due to steric effects. This interpretation is supported by the results of abinitio calculations. The data also permit a quantitative estimation of the preference for the syn configuration of lithiated imines to be at least four kcal/mol. The anti selectivity previously reported for the lithiation of endocyclic imines can be accounted for by angular constraints, as indicated by both abinitio calculations and pKa data on this class of imine.

Studies in solvolysis. Part VIII. An entropy correlation related to the reaction of various nucleophiles with malachite green

1977 ◽  
Vol 55 (4) ◽  
pp. 686-692 ◽  
Author(s):  
Stephen Harvey Morris ◽  
John Marshall William Scott ◽  
Frederick Steele
Keyword(s):  
Temperature Dependence ◽  
Malachite Green ◽  
Methyl Iodide ◽  
Rate Constants ◽  
Transition States ◽  
Reaction Coordinate ◽  
Similar Correlation ◽  
Displacement Reactions

The entropies of activation related to the reactions of aqueous malachite green with the nucleophiles water, hydroxide, hydrazine, ammonia, hypochlorite, and sulphite have been calculated from the temperature dependence of the rate constants appropriate to these reactions. The entropies of the transition states for these reactions have been characterized and the transition states shown to be 'reactant like'. A similar correlation, based on data for a series of nucleophiles attacking methyl iodide, suggests that the transition states for the SN2 displacement reactions are also 'reactant like' with respect to the attacking nucleophile. A relationship between two distinct parameters each of which is related to the position of transition states along the reaction coordinate is considered.

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