Question

Rate of hydrolysis of group P would be maximum if : (A) an amino group is substituted at \(\mathrm{C}-5\) (B) a methoxy group is substituted at C-4 (C) a nitro group is substituted at C-3 (D) a phenoxy group is substituted at C-2

Short answer

The maximum hydrolysis rate of group P would occur when an amino group is substituted at the C-5 position (option A) because the amino group is a stronger electron donor compared to the methoxy and phenoxy groups.

Step-by-step solution

Amino group at C-5

An amino group is an electron-donating substituent. If it is at the C-5 position, it will increase the electron density at the reaction center, thus increasing the rate of hydrolysis. #Step 2: Analyzing option B#

Methoxy group at C-4

A methoxy group is also an electron-donating substituent. If it is at the C-4 position, it will increase the electron density at the reaction center, similar to the amino group in option A, leading to an increased rate of hydrolysis. #Step 3: Analyzing option C#

Nitro group at C-3

A nitro group is an electron-withdrawing substituent. If it is at the C-3 position, it will decrease the electron density at the reaction center, thus reducing the rate of hydrolysis. #Step 4: Analyzing option D#

Phenoxy group at C-2

A phenoxy group is an electron-donating substituent. If it is at the C-2 position, it will increase the electron density at the reaction center, leading to an increased rate of hydrolysis. #Step 5: Comparing the options#

Comparison and conclusion

Option C shows a decrease in hydrolysis rate due to the presence of an electron-withdrawing nitro group, while options A, B, and D show an increase in hydrolysis rate due to electron-donating substituents. To find the maximum hydrolysis rate, we should compare the electron-donating power of the amino, methoxy, and phenoxy groups at their respective positions. The amino group (-NH2) is a stronger electron donor than both the methoxy and phenoxy groups. Therefore, the substitution of an amino group at the C-5 position (option A) would result in the maximum hydrolysis rate of group P.

Key concepts

Understanding Electron-Donating Substituents

Electron-donating substituents play a crucial role in organic chemistry reactions, particularly affecting the hydrolysis rate of compounds. These groups donate electron density into the π-system of a molecule, enhancing its reactivity. This happens because the added electron density can stabilize positive charges that might develop during a reaction.

Some common electron-donating substituents include:

• Amino group (-NH2)
• Methoxy group (-OCH3)
• Phenoxy group (-OPh)

Each of these groups can increase the electron density at the reaction center, leading to an increase in the reaction rate. In the exercise, placing an amino group on C-5 significantly increases the hydrolysis rate due to its strong electron-donating nature. Thus, understanding how these substituents function helps predict and control reaction mechanisms and optimize reaction conditions.

Role of Electron-Withdrawing Groups

Electron-withdrawing groups (EWGs) have the opposite effect of electron-donating groups. They lower the electron density at the reaction center, usually making a molecule less reactive in hydrolysis reactions. They pull electron density away from the π-system through inductive or resonance effects.

Common examples of EWGs are:

• Nitro group (-NO2)
• Carbonyl groups (-C=O)
• Halogens (such as -Cl, -Br, -F)

In the exercise example, the nitro group at C-3 decreases the hydrolysis rate because it withdraws electron density from the molecule's reactive site. By understanding the influence of EWGs, one can anticipate the decrease in reaction rates and aid in designing controlled and efficient synthetic routes.

Understanding Substituent Effects

The substituent effect refers to how different functional groups attached to the core molecular framework influence the overall reactivity and stability of the molecule. These effects can be broadly categorized based on whether the substituents donate or withdraw electrons, and they play a pivotal role in determining the outcome of organic reactions.

Key factors of substituent effects include:

• Position of the substituent - ortho, meta, and para positions have varying impacts.
• Type of substituent - determining electron-donating or electron-withdrawing behavior.
• Resulting changes in reaction mechanism and kinetic behavior.

In our exercise, the positioning and nature of substituents like amino, methoxy, nitro, and phenoxy groups lead to different hydrolysis rates. Recognizing these effects allows chemists to manipulate chemical reactions and synthesize desired products more efficiently.

The Basics of Organic Chemistry Reactions

Organic chemistry reactions form the foundation of understanding complex chemical behavior in organic compounds. These reactions are often influenced by the substituents present, as well as reaction conditions. Hydrolysis, in particular, involves the breaking of a bond in a molecule using water.

Some key components of these reactions include:

• Reaction mechanisms - step-by-step pathways showing the movement of electrons.
• Reaction kinetics - study of rate, determining how fast the reaction proceeds.
• Impact of different substituents - altering reactivity and selectivity.

In the exercise, analyzing different substituents allows us to determine the conditions under which maximum hydrolysis rate occurs. By mastering these reactions, students can better predict outcomes, improve reaction efficiency and leverage their chemical knowledge for practical applications.