Problem 69 - Arihant Objective Approach to Organic Chemistry for IIT JEE and NEET all Medical Entrances Part 4

Question

When glucose reacts with bromine water the main product is : [HR (PMT) 1997] (a) gluconic acid (b) glyceraldehyde (c) sorbitol (d) saccharic acid

Step-by-Step Solution

Answer

The main product is gluconic acid (option a).

Step 1: Identifying the Reaction Type

The reaction involves glucose ( C_6H_{12}O_6 d) and bromine water ( Br_2 ) which typically leads to an oxidation reaction where aldehyde groups are oxidized to carboxylic acids.

Step 2: Recognizing Functional Groups in Glucose

Glucose is an aldose sugar and contains an aldehyde group at the C-1 position. This group is susceptible to oxidation in the presence of bromine water.

Step 3: Predicting the Reaction Outcome

In the presence of bromine water, the aldehyde group in glucose is oxidized to form gluconic acid, where the aldehyde group at C-1 becomes a carboxylic acid group. Hence, gluconic acid ( C_6H_{12}O_7 ) is formed.

Step 4: Selecting the Correct Answer

Based on the prediction from the previous step, the correct answer is gluconic acid, making option (a) the correct choice.

Key Concepts

Oxidation Reaction in Organic Chemistry

In organic chemistry, oxidation reactions are fundamental processes that involve the transfer of electrons. Generally speaking, an oxidation reaction involves the increase of the oxygen content or a decrease in hydrogen content of a molecule.
One of the most common forms of oxidation in organic compounds is the transformation of an aldehyde group to a carboxylic acid.
In simpler terms, an aldehyde (\( -CHO \)) has the potential to gain an oxygen atom, thus turning into a carboxylic acid (\( -COOH \)).
This type of reaction is crucial in the metabolism of carbohydrates and plays an important role in the transformation of sugars.
When glucose, a simple sugar, reacts with bromine water (\( Br_2 \)), the aldehyde group is oxidized. Glucose contains an aldehyde group at the first carbon (C-1). This group is readily oxidized to a carboxylic acid group, forming gluconic acid.
Such reactions not only change the structure of the molecule, but they also significantly alter its chemical properties.

Functional Groups in Carbohydrates

Carbohydrates are a major class of biomolecules that include sugars and starches.
A functional group is a specific group of atoms within a molecule that is responsible for a characteristic reaction of that molecule.
Glucose, for example, contains several functional groups that define its chemical behavior:

• Aldehyde Group: Present at the first carbon (C-1), it is highly reactive and can be easily oxidized.
• Hydroxyl Groups: Found on the other carbons, these groups (\( -OH \)) engage in hydrogen bonding and solubility.

These functional groups are critical in glucose's reactivity, particularly in reactions involving oxidation, such as with bromine water.
Recognizing these functional groups helps us understand how glucose transforms into different derivatives with varied properties.

Aldose Sugar Reactions

Aldose sugars are simple carbohydrates that contain an aldehyde group.
Because of this, they are very reactive and participate in numerous chemical reactions.
In the context of glucose, which is the most common aldose sugar, reactions usually involve the aldehyde group at the C-1 position.

• The reaction with bromine water is a classic example where the aldehyde group gets oxidized to a carboxylic acid.
• This transformation results in the formation of gluconic acid (\( C_6H_{12}O_7 \)), which is a notable process in carbohydrate chemistry.

Understanding these reactions of aldose sugars helps in grasping broader concepts in biochemistry, including metabolic pathways and energy production.
It emphasizes the importance of functional groups and how their specific chemistry leads to consequential biological roles.