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Information about the mechanism of the reaction undergone by a series of substituted benzenes can be obtained by plotting the logarithm of the observed rate constant determined at a particular pH against the Hammett substituent constant (o) for the particular substituent. The o value for hydrogen is 0. Electron-donating substituents have negative o values; the more strongly electron donating the substituent, the more negative its o value. Electron-withdrawing substituents have positive o values; the more strongly electron withdrawing the substituent, the more positive its o value. The slope of a plot of the logarithm of the rate constant versus o is called the p (rho) value. The p value for the hydroxide-ion-promoted hydrolysis of a series of meta- and para-substituted ethyl benzoates is +2.46; the p value for amide formation for the reaction of a series of meta- and para-substituted anilines with benzoyl chloride is -2.78. OCH,CH3 OCH,CH3 OCH,CH3 ortho-substituted meta-substituted para-substituted a. Why does one set of experiments give a positive p value, whereas the other set of experiments gives a negative p value? b. Why were ortho-substituted compounds not included in the experiment? c. What do you predict the sign of the p value to be for the ionization of a series of meta- and para-substituted benzoic acids?

Information about the mechanism of the reaction undergone by a series of substituted benzenes can be obtained by plotting the logarithm of the observed rate constant determined at a particular pH against the Hammett substituent constant (o) for the particular substituent. The o value for hydrogen is 0. Electron-donating substituents have negative o values; the more strongly electron donating the substituent, the more negative its o value. Electron-withdrawing substituents have positive o values; the more strongly electron withdrawing the substituent, the more positive its o value. The slope of a plot of the logarithm of the rate constant versus o is called the p (rho) value. The p value for the hydroxide-ion-promoted hydrolysis of a series of meta- and para-substituted ethyl benzoates is +2.46; the p value for amide formation for the reaction of a series of meta- and para-substituted anilines with benzoyl chloride is -2.78. OCH,CH3 OCH,CH3 OCH,CH3 ortho-substituted meta-substituted para-substituted a. Why does one set of experiments give a positive p value, whereas the other set of experiments gives a negative p value? b. Why were ortho-substituted compounds not included in the experiment? c. What do you predict the sign of the p value to be for the ionization of a series of meta- and para-substituted benzoic acids?

Chemistry
Chemistry
10th Edition
ISBN:9781305957404
Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Chapter1: Chemical Foundations
Section: Chapter Questions
Problem 1RQ: Define and explain the differences between the following terms. a. law and theory b. theory and...
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Information about the mechanism of the reaction undergone by a series of substituted benzenes can be obtained by plotting the logarithm of the observed rate constant determined at a particular pH against the Hammett substituent constant (o) for the particular substituent. The o value for hydrogen is 0. Electron-donating substituents have negative o values; the more strongly electron donating the substituent, the more negative its o value. Electron-withdrawing substituents have positive o values; the more strongly electron withdrawing the substituent, the more positive its o value. The slope of a plot of the logarithm of the rate constant versus o is called the p (rho) value. The p value for the hydroxide-ion-promoted hydrolysis of a series of meta- and para-substituted ethyl benzoates is +2.46; the p value for amide formation for the reaction of a series of meta- and para-substituted anilines with benzoyl chloride is -2.78. OCH,CH3 OCH,CH3 OCH,CH3 ortho-substituted meta-substituted para-substituted a. Why does one set of experiments give a positive p value, whereas the other set of experiments gives a negative p value? b. Why were ortho-substituted compounds not included in the experiment? c. What do you predict the sign of the p value to be for the ionization of a series of meta- and para-substituted benzoic acids?
Transcribed Image Text:Information about the mechanism of the reaction undergone by a series of substituted benzenes can be obtained by plotting the logarithm of the observed rate constant determined at a particular pH against the Hammett substituent constant (o) for the particular substituent. The o value for hydrogen is 0. Electron-donating substituents have negative o values; the more strongly electron donating the substituent, the more negative its o value. Electron-withdrawing substituents have positive o values; the more strongly electron withdrawing the substituent, the more positive its o value. The slope of a plot of the logarithm of the rate constant versus o is called the p (rho) value. The p value for the hydroxide-ion-promoted hydrolysis of a series of meta- and para-substituted ethyl benzoates is +2.46; the p value for amide formation for the reaction of a series of meta- and para-substituted anilines with benzoyl chloride is -2.78. OCH,CH3 OCH,CH3 OCH,CH3 ortho-substituted meta-substituted para-substituted a. Why does one set of experiments give a positive p value, whereas the other set of experiments gives a negative p value? b. Why were ortho-substituted compounds not included in the experiment? c. What do you predict the sign of the p value to be for the ionization of a series of meta- and para-substituted benzoic acids?
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