Question

Which of the following would be most reactive toward nucleophiles? (A) Propyl ethanoate (B) Propanoic acid (C) Propanamide (D) Propanoic anhydride

Short answer

Propanoic anhydride (D)

Step-by-step solution

Identify functional groups

Review the functional groups in each compound.(A) Propyl ethanoate: ester(B) Propanoic acid: carboxylic acid(C) Propanamide: amide(D) Propanoic anhydride: anhydride

Evaluate electrophilicity

Recognize that more reactive compounds toward nucleophiles have more electrophilic carbon atoms. Electrophilicity generally follows the pattern: anhydrides > esters > carboxylic acids > amides.

Determine reactivity

Since anhydrides are the most electrophilic and most reactive toward nucleophiles amongst the given options, identify which compound is an anhydride.

Choose the correct option

Propanoic anhydride (D) is the compound with an anhydride functional group, making it the most reactive toward nucleophiles.

Key concepts

Functional Groups

Functional groups are specific groups of atoms within molecules that determine the characteristic chemical reactions of those molecules. They play a crucial role in the reactivity and properties of organic compounds.
For example, in the exercise provided, the functional groups are:

• Propyl ethanoate: ester
• Propanoic acid: carboxylic acid
• Propanamide: amide
• Propanoic anhydride: anhydride

Identifying functional groups is the first step in solving many organic chemistry problems. Each group has unique reactivity patterns that influence the behavior of the entire molecule in chemical reactions.

Electrophilicity

Electrophilicity refers to the ability of a molecule to accept electrons. Electrophiles are species that are electron-deficient and look to gain electrons.
In organic chemistry, electrophilic centers are usually carbon atoms that are bonded to electronegative atoms such as oxygen or halogens, making them partially positive. These partial positive charges attract nucleophiles, which are electron-rich agents.
For example, in this exercise, we observed that anhydrides are more electrophilic than esters, carboxylic acids, and amides. This order is important for predicting and understanding the reactivity in nucleophilic substitution reactions.

Organic Chemistry Problem-Solving

Problem-solving in organic chemistry often involves applying a structured approach:

• Identify the functional groups involved.
• Determine the electrophilic centers in the molecules.
• Evaluate the relative reactivity based on known trends and properties (such as the electrophilicity).
• Select the correct option based on the analysis.

By following these steps, students can systematically approach and solve complex problems. In our example, we identified the functional groups and then assessed the electrophilicity to find the most reactive compound toward nucleophiles.

Reactivity Order

Reactivity order is a ranking based on how readily different compounds undergo chemical reactions. This order helps predict which molecules will react faster or more readily in a given set of conditions.
In the context of the exercise, the reactivity order toward nucleophiles is:

• Anhydrides > Esters > Carboxylic acids > Amides

This means anhydrides are the most reactive, followed by esters, carboxylic acids, and amides. Understanding this hierarchy allows chemists to predict outcomes and plan synthesis pathways efficiently.
In the provided problem, recognizing this order helped us conclude that propanoic anhydride (D) is the most reactive toward nucleophiles.