Problem 171 - A Complete Resource Book in Chemistry for JEE Main

Question

Cc1ccc(O)c(C(=O)O)c1 is __ . # The number of acidic hydrogen which reacts with RMgBr in the molecule C#Cc1ccc(O)c(C(=O)O)c1 is __ .

Step-by-Step Solution

Answer

The molecule has 1 acidic hydrogen.

Step 1: Identify Acidic Hydrogens

Given the structure of the compound as a SMILES string, we need to identify the acidic hydrogens. Look for carboxylic acid groups (COOH) as they typically release acidic hydrogens when reacting with strong bases like RMgBr.

Step 2: Analyze the Structure from SMILES

The SMILES string "C#Cc1ccc(O)c(C(=O)O)c1" represents a molecule with a carboxylic acid group (C(=O)O). In this group, the hydrogen attached to the oxygen (OH) is acidic.

Step 3: Count the Acidic Hydrogens

In the given SMILES, there is a single carboxylic acid group. Each carboxylic acid group contains one hydrogen in the hydroxyl group (OH) that is considered acidic.

Step 4: Conclusion on Number of Acidic Hydrogens

Since there is one carboxylic acid group in the molecule, there is one acidic hydrogen that can react with RMgBr.

Key Concepts

Carboxylic Acid

Carboxylic acids are organic compounds characterized by the presence of a carboxyl group, which consists of a carbon double-bonded to an oxygen (C=O) and a hydroxyl group (OH) attached to the same carbon atom. This group is often denoted by

• C(=O)OH
• or as COOH in simpler representations

Carboxylic acids are known for their ability to donate a proton (H+) to a base, acting as weak acids.
In the context of Grignard reactions, the hydrogen in the hydroxyl (OH) of the carboxylic acid group is particularly noteworthy because it is the acidic hydrogen that can easily react with Grignard reagents like RMgBr.
This reactivity is due to the polar nature of the O-H bond, which makes the hydrogen more exposed and prone to be released in the presence of strong bases or reactive magnesium species.

SMILES Representation

The Simplified Molecular Input Line Entry System (SMILES) is a notation that allows chemists to represent a molecule’s structure using a string of text.
This system simplifies the description of complex organic molecules, enabling easy sharing and digital storage of chemical information.

• The SMILES string depicts the connectivity and conformation of atoms within a molecule without the need for a graphical molecular structure.

For example, in the SMILES string "C#Cc1ccc(O)c(C(=O)O)c1",

• 'C#C' represents a triple bond between two carbon atoms,
• 'c1ccc(O)c' denotes a benzene ring with a hydroxyl group (OH) substituent.

The portion 'C(=O)O' displays the carboxyl group, emphasizing its presence and position within the molecule.

Grignard Reaction

The Grignard reaction is a fundamental reaction in organic chemistry that involves the use of Grignard reagents.
These reagents, designated as RMgX (where R is an organic group and X is a halide), are highly reactive and useful in forming carbon-carbon bonds.

• They are prepared by reacting magnesium metal with an alkyl or aryl halide.
• Grignard reagents act as strong nucleophiles and bases, making them capable of reacting with compounds containing acidic hydrogens, such as carboxylic acids.

When a Grignard reagent encounters a carboxylic acid, a salt of the carboxylate anion forms, and a hydrocarbon (RH) is released.
This reaction is a vital tool for synthesizing alcohols by adding carbon chains to carbonyl compounds.

Hydrogen Reactivity

Hydrogen's reactivity is influenced by its environment in a molecule.
In carboxylic acids, the hydrogen of the hydroxyl group is notably reactive due to its acidic nature.

• This makes it susceptible to reactions with strong bases and organometallic compounds like Grignard reagents.
• The ease with which it can be released as a proton (H+) makes it key in many chemical transformations.

When reacting with a Grignard reagent, the acidic hydrogen is replaced by a magnesium halide, forming a stable carboxylate salt and freeing a hydrocarbon molecule (RH).
Understanding the reactivity of hydrogens in various environments allows chemists to predict and manipulate chemical reactions effectively, enabling the synthesis of a wide range of organic compounds.