Problem 70 - A Complete Resource Book in Chemistry for JEE Main

Question

Consider the following alcohols ( \(\varphi\) is \(\mathrm{C}_{6} \mathrm{H}_{5}\) ) CCC(O)O OCCCc1ccccc1 CC(O)CO (1) (2) (3) The correct order of reactivity of these alcohols to ether is (a) \(1>2>3\) (b) \(2>1>3\) (c) \(1>3>2\) (d) \(2>3>1\)

Step-by-Step Solution

Answer

The correct order is (b) 2>1>3.

Step 1: Identify the Alcohols

First, let's determine the structure of the alcohols from the provided SMILES. 1. CCC(O)O is propylene glycol with two terminal alcohol groups. 2. OCCCc1ccccc1 is benzyl alcohol with the formula C6H5CH2CH2OH. 3. CC(O)CO is propane-1,2-diol, a diol with hydroxyl groups on adjacent carbons.

Step 2: Understand Ether Formation Reactivity

To form ethers from alcohols, protons from the hydroxyl groups are removed. Generally, primary alcohols are more reactive than secondary or tertiary alcohols due to less steric hindrance, allowing easier formation of ethers. Additionally, benzyl alcohol (2) exhibits high reactivity due to resonance stabilization, increasing its propensity to form ethers.

Step 3: Compare Reactivities

Analyzing the identified alcohols for ether formation: - Benzyl alcohol (2) is the most reactive due to its resonance stability, favoring ether formation. - Propylene glycol (1) has two hydroxyl groups, providing more opportunity for ether formation than propane-1,2-diol (3). - Therefore, the order of reactivity to form an ether is 2 > 1 > 3.

Key Concepts

Ether Formation

Ether formation from alcohols involves removing the protons from the hydroxyl groups. This process results in the creation of an ether bond (
1C
1O
1C). Generally speaking, primary alcohols are more reactive when it comes to ether formation compared to secondary and tertiary alcohols.
This is mainly due to the lower steric hindrance they possess, which allows the reaction to proceed more efficiently.
Primary alcohols have their hydroxyl group connected to a central carbon atom that is, at most, bonded to one other carbon, making them more accessible to reactants. Consideration of these features helps predict which alcohols might engage better in ether formation. Benzyl alcohol exhibits even higher reactivity. The presence of the benzyl group provides resonance stability, which significantly enhances its ability to form ethers. This stable conformation eases ether formation, making alcohols with resonance structures exceptionally reactive for this process.

Benzyl Alcohol Reactivity

Benzyl alcohol is unique in its enhanced reactivity due to resonance. Resonance stabilization involves the delocalization of electrons over a benzene ring, offering more stability to the structure.
When benzyl alcohol reacts to form ethers, it has an advantage. The benzyl group provides a conjugated system where electron density can be easily shifted, making it more reactive in forming new bonds.
This enhanced reactivity is often why benzyl alcohol is favored in reactions involving ether formation. Compared to other alcohols without this stabilization feature, benzyl alcohol more readily undergoes reactions due to the stability provided by its structure.

SMILES Notation

SMILES notation, or Simplified Molecular Input Line Entry System, is an effective method for representing a molecule's structure using a linear text format. It simplifies complex chemical structures and is widely used in cheminformatics.
For instance, the SMILES
1"CCC(O)O"
1 describes propylene glycol, indicating the linear chain of carbon atoms bonded to an alcohol group. SMILES notation provides a quick method to understand molecular composition without needing a visual diagram.
In our problem, SMILES was used to determine the types of alcohols present and predict their reactivity in ether formation. Understanding SMILES is crucial for identifying alcohols and analyzing potential reactions, especially in academics and research settings.