Question

The correct statement(s) for compound is/are (A) Aldohexose (B) Pyranose form (C) \(\mathrm{C}_{4}\)-epimer of glucose (D) Non-reducing sugar

Short answer

The correct statements for a compound are (A) Aldohexose, (B) Pyranose form, and (C) \(\mathrm{C}_{4}\)-epimer of glucose. Statement (D) Non-reducing sugar is not universally correct.

Step-by-step solution

Understanding aldohexose

An aldohexose is a hexose (a monosaccharide containing six carbon atoms) with an aldehyde group at the first carbon atom. Examples include glucose and galactose.

Understanding Pyranose form

A pyranose form is a cyclic structure formed when the carbonyl group of a monosaccharide reacts with a hydroxyl group on another carbon atom, forming a hemiacetal or hemiketal. In the case of a pyranose, this structure resembles the six-membered ring of pyran. The most prevalent pyranose forms are derived from aldohexoses, such as glucose and galactose.

Understanding an Epimer

An epimer is a pair of diastereomers that differs in the configuration at only one carbon atom. An example is glucose and galactose, which differ only in the configuration at the C-4 carbon atom. They are C-4 epimers of each other.

Understanding Reducing Sugars

A reducing sugar is a carbohydrate with a free aldehyde or ketone group, making it capable of reducing other compounds in a chemical reaction. Examples of reducing sugars include glucose and galactose. Non-reducing sugars are those carbohydrates that lack a free aldehyde or ketone group, such as sucrose. Now let's evaluate each statement:

Statement (A) Aldohexose

This is a correct statement because a compound can be an aldohexose. It's a type of monosaccharide with six carbon atoms and an aldehyde group at the first carbon atom.

Statement (B) Pyranose form

This is also a correct statement, as a compound can be in pyranose form, especially aldohexoses. It is a cyclic structure resembling the six-membered ring of pyran, obtained from the reaction between the carbonyl group and a hydroxyl group within the monosaccharide.

Statement (C) \(\mathrm{C}_{4}\)-epimer of glucose

This statement is correct. A compound can be a \(\mathrm{C}_{4}\)-epimer of glucose, which means it differs from glucose only in the configuration at the C-4 carbon atom. An example of a \(\mathrm{C}_{4}\)-epimer of glucose is galactose.

Statement (D) Non-reducing sugar

This statement is not universally correct because a compound can be either a reducing or a non-reducing sugar depending on its structure. Non-reducing sugars lack a free aldehyde or ketone group, making them unable to reduce other compounds in a chemical reaction. In conclusion, the correct statements for a compound are (A) Aldohexose, (B) Pyranose form, and (C) \(\mathrm{C}_{4}\)-epimer of glucose. Statement (D) Non-reducing sugar is not universally correct.

Key concepts

Aldohexose

An aldohexose is a specific type of monosaccharide. Monosaccharides are simple sugars that are basic units of carbohydrates. Aldohexoses are characterized by two main features:

• They contain six carbon atoms in their structure, which classifies them as hexoses.
• They possess an aldehyde group attached to their first carbon atom, hence the 'aldo' prefix.

Examples of aldohexoses include glucose and galactose, both crucial for energy metabolism. Aldohexoses can exist in either linear or cyclic forms, though the cyclic form is more stable and prevalent in nature.

Pyranose form

The pyranose form represents the cyclic form that certain monosaccharides can assume. This circular structure forms when the carbonyl group reacts with a hydroxyl group
. The result is a hemiacetal or hemiketal, depending on the type of monosaccharide.

• Pyranoses typically have a six-membered ring structure.
• The arrangement resembles the chemical structure of pyran, a simple organic compound.

Aldohexoses like glucose often form pyranose rings. This configuration is more stable, making it a common formation in biological systems. When you hear the term pyranose, think of a closed-ring sugar structure resembling a hexagon.

Epimers

Epimers are a special subset of stereoisomers. These molecules are identical in all respects except for one critical detail:

• They differ in configuration at just one specific carbon atom.

For example, glucose and galactose are C-4 epimers, differing only at their fourth carbon. This single variation can lead to significantly different properties and biochemical roles, even though their overall chemical structures are quite similar. Epimers are crucial in carbohydrate chemistry because such small changes can affect a sugar's biochemical pathways and interactions.

Reducing sugars

Reducing sugars are carbohydrates that have the ability to reduce other substances, a trait springing from a particular structural feature.

• This characteristic is due to the presence of a free aldehyde or ketone group.

In basic solutions, the open-chain form of these sugars can function as reducing agents, participating in redox reactions,

• Glucose and galactose are examples of reducing sugars.

On the contrary, non-reducing sugars, like sucrose, lack this free group, rendering them unable to participate in such reactions. Understanding whether a sugar is reducing or non-reducing is vital for its identification and determination of its potential chemical reactions.