Protonation of the Amide Group: I. The Basicities of Substituted Benzamides

Section: Ch3mentioning

confidence: 70%

Tryptamines, Carbolines, and Related Compounds: Part Vii. Internuclear Cyclization Onto a Pyridine Ring

Abramovitch¹

1960

“…substituted benzamides was reported previously (10). Since this was better than the correlation between a+ and pK, it was taken as evidence of a lack of conjugation between the protonated carboxamide group and phenyl ring.…”

Section: Lfinear Free Energy Lielations a Good Linear Correlation Betmentioning

confidence: 79%

“…This confirms the earlier conclusion. Several suggestions have been advanced (6,10) to explain this lack of conjugation in amides but as yet there is no evidence to indicate which, if any, is correct. From the above pR-a relation, the correct Hammett p-value for the equilibrium is -0.92, which is appreciably lower than previously reported.…”

Section: Lfinear Free Energy Lielations a Good Linear Correlation Betmentioning

confidence: 99%

THE IONIZATION BEHAVIOR OF AMIDES IN CONCENTRATED SULFURIC ACIDS: II. APPLICATIONS OF THE H_A FUNCTION TO RATES AND EQUILIBRIA

Yates¹,

Stevens²

1965

ABSTRACT'The newly determined H. 4 scale of acidity has been tested against ionization ratio data for 33 amides. Twenty-nine of these compounds give log I vs. HA slopes of 0.9-1.1 and most are within 0.95-1.05. The average slope for these is 1.001 f 0.051. 'The H. 4 function is thus considered to be generally applicable to the ionization of this type of base, and the significance of previously reported amide p K values is discussed in the light of these results. Previously reported basicity-substituent constant relations have been reexamined using thermodynamically significant p K data and earlier conclusions confirmed. Appropriate ecluations are derived in an attempt to explain the rate-acidity dependence of amide hydrolysis directly in terms of the water activity of the reaction medium. 'The picture of the hydrolysis t r a~~s i t i o n state which results is in accord with that obtained using methods described by other workers.

“…4B, in which the curve has been calculated assuining pKBH+ = -1.0, E, = 2260, and EBH+ = 260. I t is found that the experinlental poiilts for propionamide deviate fro111 the theoretical curve in a manner which is characteristic for all alnides so far studied (4,25,31): in the neighborhood of the inflection point, the slope of the experimental curve is always less than theoretical (i.e. increase of ho produces a smaller increase in the ionization ratio than predicted by equation [2]).…”

Section: Calculation Of Protonation Constants Of Propionamidementioning

confidence: 83%

“…4), the protonation constant of propionanlide lnay be FIG. 4. Ionization of propionainide in sulphuric acid.…”

Section: Calculation Of Protonation Constants Of Propionamidementioning

confidence: 99%

Ionization of Organic Compounds: Iii. Basicities of Propionic Acid and Propionamide

Edward¹,

Wang²

1962

Self Cite

Protonation constants (pKBH+) of −6.8 and −0.9 have been determined for propionic acid and propionamide, respectively, from measurements of their ultraviolet absorption in various concentrations of sulphuric acid. The ionization ratio of propionamide and of other amides increases more slowly than the Hammett acidity function, h0, with increase in acid concentration. This may be explained by assuming that in a given concentration of sulphuric acid the protonated amide is more heavily hydrated than the protonated Hammett indicator used to establish the h0 scale for this region of acid concentrations.