Problem 25 - Chemistry in 30 days

Question

Consider the following compounds: (i) ClC(Cl)(Cl)c1ccccc1 (ii) O=C(Cl)c1ccc([N+](=O)[O-])cc1(iii) Cc1ccc(C(=O)Cl)cc1 (iv) O=Cc1ccc(C(=O)Cl)cc1 the correct decreasing order of their reactivity towards hydrolysis is (a) \((\mathrm{iv})>(\mathrm{ii})>(i)>\) (iii) (b) (ii) \(>(i v)>(i)>\) (iii) (c) (ii) > (iv) > (iii) > (i) (d) \((i)>(i i)>(i i i)>(i v)\)

Step-by-Step Solution

Answer

(c) (ii) > (iv) > (iii) > (i)

Step 1: Understand the Basics of Hydrolysis

Hydrolysis is a chemical reaction that involves the breaking of a bond in a molecule using water. Organic compounds with acyl chlorides tend to undergo hydrolysis due to the high electrophilicity of the carbonyl carbon.

Step 2: Identify Functional Groups

Identify and label the functional groups in the given compounds: (i) is a polychlorinated aromatic compound (benzene ring with CCl3 group), (ii) is a nitro aromatic acyl chloride, (iii) is an aromatic acyl chloride, and (iv) is a benzaldehyde derivative with an acyl chloride group.

Step 3: Assess Electrophilicity

The reactivity of acyl chlorides towards hydrolysis depends on the electron-withdrawing ability of substituents attached to the aromatic ring, which affects electrophilicity. Compounds (ii) and (iv) have electron-withdrawing groups (NO2 and aldehyde group, respectively) that increase electrophilicity of the acyl chloride.

Step 4: Rank Based on Reactivity

With electrophilicity in mind, determine the order of reactivity. (ii) with a nitro group is the most electrophilic, making it the most reactive towards hydrolysis. (iv) follows due to the aldehyde group, then (iii) which is a simple acyl chloride, and lastly (i) which lacks the acyl chloride group altogether.

Step 5: Select the Correct Option

Based on the ranking, the decreasing order of reactivity towards hydrolysis is (ii) > (iv) > (iii) > (i). Thus, the correct option is (c).

Key Concepts

Hydrolysis

Hydrolysis is an important chemical reaction in organic chemistry where a molecule is split into two parts through the addition of water. This process can be thought of as a "water-initiated breakage." In the context of acyl chlorides, hydrolysis typically involves breaking the bond between the acyl group and the chloride ion.

• During hydrolysis, water donates an oxygen and two hydrogens. This donation leads to the formation of an acid and hydrochloric acid.
• Hydrolysis is common with acyl chlorides due to their reactive nature.

Understanding hydrolysis is crucial as it highlights the role of water in breaking molecular bonds. This function allows for the transformation of acyl chlorides into more stable compounds, like carboxylic acids.

Electrophilicity

Electrophilicity describes how susceptible a molecule is to accepting electrons in a chemical reaction. The higher the electrophilicity, the more reactive the molecule is.

• Compounds with high electrophilicity are typically strong Lewis acids, meaning they have a strong tendency to accept electron pairs.
• In the context of acyl chlorides, the presence of electron-withdrawing groups enhances their electrophilicity.
• Electrophilicity affects how different functional groups in organic molecules react, particularly in hydrolysis.

A compound's electrophilicity can significantly influence its behavior in organic reactions, with electron-withdrawing groups increasing its reactivity by making it more eager to accept electrons.

Functional Groups

Functional groups are specific groups of atoms within molecules that have characteristic properties and reactions. Recognizing these groups is vital to understanding the behavior of different compounds.

• Every functional group has a specific arrangement of atoms that shows consistent properties.
• Functional groups determine the chemical reactivity and interactions of molecules.
• Examples include acyl chlorides, nitro groups, and aldehydes.

Knowing functional groups helps us predict the reactivity of organic compounds. For instance, an acyl chloride group is highly reactive because of its ability to easily undergo hydrolysis.

Acyl Chlorides

Acyl chlorides, also known as acid chlorides, are a specific type of carboxylic acid derivative where the hydroxyl group is replaced with a chlorine atom. They serve as an important functional group in organic chemistry due to their high reactivity.

• Acyl chlorides are notorious for reacting with nucleophiles, especially in hydrolysis reactions.
• They are typically considered among the most reactive carboxylic acid derivatives.
• Their reactivity is influenced by the presence of substituents. Electron-withdrawing groups enhance their reactivity, as seen with compounds containing nitro or aldehyde groups.

Understanding acyl chlorides is essential in organic synthesis, especially when considering the production of carboxylic acids. This knowledge allows chemists to manipulate chemical reactions for desired outcomes.