Ch. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions

Bruice8th EditionOrganic ChemistryISBN: 9780135213711Not the one you use?Change textbook

Bruice 8th Edition

Ch. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions

Problem 12

Chapter 23, Problem 12

Why do the nitro groups change the relative leaving tendencies of the carboxy and 2,4-dinitrophenoxy groups in the tetrahedral intermediate in Problem 11?

Verified step by step guidance

Step 1: Analyze the structure of the tetrahedral intermediate. The intermediate contains two potential leaving groups: the carboxy group (-COO⁻) and the 2,4-dinitrophenoxy group (-OAr, where Ar is the 2,4-dinitrophenyl ring). Both groups are attached to the central carbon atom.

Step 2: Consider the electronic effects of the nitro groups on the 2,4-dinitrophenoxy group. Nitro groups are electron-withdrawing due to their strong -I (inductive) and -M (mesomeric) effects. These effects stabilize the negative charge on the phenoxide ion (ArO⁻) that forms when the 2,4-dinitrophenoxy group leaves.

Step 3: Compare the leaving group tendencies. The carboxy group (-COO⁻) is also a good leaving group due to resonance stabilization of the carboxylate ion. However, the presence of two nitro groups on the phenoxy group significantly enhances its ability to act as a leaving group by stabilizing the negative charge more effectively than the carboxylate ion.

Step 4: Evaluate the relative leaving group tendencies in the context of the reaction mechanism. The 2,4-dinitrophenoxy group is more likely to leave because the nitro groups increase its leaving group ability, making it more favorable for the reaction to proceed via the elimination of this group.

Step 5: Conclude that the nitro groups change the relative leaving tendencies by stabilizing the phenoxide ion through electron-withdrawing effects, thereby making the 2,4-dinitrophenoxy group a better leaving group compared to the carboxy group in the tetrahedral intermediate.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.

Video duration:

Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Tetrahedral Intermediates

Tetrahedral intermediates are key species in nucleophilic acyl substitution reactions, formed when a nucleophile attacks a carbonyl carbon, resulting in a four-coordinate carbon atom. In this context, the stability of the tetrahedral intermediate is influenced by the substituents on the aromatic ring, such as nitro groups, which can affect the electron density and sterics around the leaving groups.

Leaving Group Ability

The ability of a leaving group to depart from a molecule is crucial in determining the rate of a reaction. Good leaving groups are typically stable after departure, while poor leaving groups are less stable. In this case, the presence of nitro groups can enhance the leaving ability of certain groups by stabilizing the negative charge that develops during the transition state.

Electron-Withdrawing Groups

Electron-withdrawing groups, such as nitro groups, can significantly influence the reactivity of organic compounds. They stabilize negative charges through resonance or inductive effects, which can enhance the leaving tendencies of groups attached to the same molecule. In the context of the question, the nitro groups affect the relative leaving tendencies of the carboxy and 2,4-dinitrophenoxy groups by altering the electronic environment of the tetrahedral intermediate.

Recommended video:

Guided course

02:37

Donating vs Withdrawing Groups

Related Practice

Textbook Question

Although metal ions increase the rate of decarboxylation of dimethyloxaloacetate, they have no effect on the rate of decarboxylation of either the monoethyl ester of dimethyloxaloacetate or acetoacetate. Explain why this is so.

1391

views

Textbook Question

Draw the pH–activity profile for an enzyme that has one catalytic group at the active site:

a. the catalytic group is a general-acid catalyst with a pK_a = 5.6.

925

views

Textbook Question

The relative rate of reaction for the cis alkene (E) is given in Table 22.2. What do you expect the relative rate of reaction for the trans alkene to be?

1239

views

Textbook Question

Which of the following C-terminal peptide bonds is more readily cleaved by carboxypeptidase A? Explain your choice.

Ser-Ala-Leu or Ser-Ala-Asp

1194

views

Textbook Question

Show all the products, including their configurations, that are obtained from the above reaction.

1023

views

Textbook Question

Which of the following amino acid side chains can help remove a proton from the α-carbon of an aldehyde?

3080

views