Question

The incorrect statement is (A) Galactose and glucose are epimers (B) Glucose and mannose are anomers (C) Glucose and fructose both can show mutarotation (D) \(\alpha\)-D-Glucopyranose and \(\beta\)-D-Glucopyranose both are stereoisomers

Short answer

The incorrect statement is (B) Glucose and mannose are anomers. They are actually epimers, not anomers, as they differ in the configuration around carbon-2.

Step-by-step solution

Understanding the terms

Before we can analyze each statement, let's review the definitions of each term: 1. Epimers: Epimers are two sugars that differ only in the configuration around one carbon atom. 2. Anomers: Anomers are stereoisomers of a sugar that differ in configuration only at the anomeric carbon (the carbon derived from the carbonyl group). 3. Mutarotation: Mutarotation is the process where the specific rotation of an optically active substance gradually changes to a constant value when dissolved in a solution. 4. Stereoisomers: Stereoisomers are compounds with the same molecular formula and sequence of bonded atoms but differ in the three-dimensional orientation of their atoms in space.

Analyzing each statement

(A) Galactose and glucose are epimers: This statement is correct. Galactose and glucose differ in the configuration around one carbon atom (carbon-4). (B) Glucose and mannose are anomers: This statement is incorrect. Glucose and mannose differ in the configuration around carbon-2. They are epimers, not anomers. (C) Glucose and fructose both can show mutarotation: This statement is true. Both glucose and fructose have multiple anomeric forms that can undergo mutarotation in solution. (D) \(\alpha\)-D-Glucopyranose and \(\beta\)-D-Glucopyranose both are stereoisomers: This statement is correct. Alpha and beta forms of D-Glucopyranose differ in the configuration only at the anomeric carbon, making them stereoisomers.

Identifying the incorrect statement

Based on our analysis, the incorrect statement is (B) Glucose and mannose are anomers.

Key concepts

Epimers

Epimers are a fascinating type of stereoisomers that you'll encounter when delving into the world of carbohydrates. They are sugars that share a very similar structure, with just a slight twist: epimers only differ in the orientation of the atoms around one specific carbon atom, excluding the anomeric carbon.

Imagine two nearly identical houses on your street, with just one window different – that's a bit like epimers. For instance, the well-known sugars galactose and glucose are different just at carbon-4. They're like carbohydrate twins with one distinct feature setting them apart.

• To recall, epimers are not the same as anomers, which differ at the anomeric carbon - typically the first carbon in the sugar.
• The importance of this small difference is huge biologically since epimers can have different properties and functions within living organisms.

Anomers

Anomers refer to a special kind of stereoisomers specific to the cyclical forms of sugars. In carbohydrates, the anomeric carbon is formed when a carbohydrate cyclizes, and the former carbonyl carbon (carbon-1 in aldoses, carbon-2 in ketoses) becomes a new chiral center.

Think of a sugar molecule as a flexible dancer that can assume two different poses, known as \/ Occurrence of anomers is a defining characteristic of sugars when they form cyclic structures, which is critical in biology for how these molecules behave and interact.

• \( \alpha \)- and \( \beta \)-anomers are the two possible orientations, distinguished by the position of the substituent on the anomeric carbon relative to the cyclic molecule.
• Anomers have distinct physical properties, like solubility and sweet taste, which can be important for food science and pharmaceuticals.

Mutarotation

Mutarotation is like a little performance that molecules put on when they dissolve in water. When a sugar with an anomeric carbon (like glucose or fructose) is dissolved, it doesn't just sit there – it changes forms. Specifically, the \/ Mutarotation is seen as a change in the specific optical rotation, which is a measure of how much a compound can rotate plane-polarized light.

If you're trying to imagine it, think about a revolving door changing speed as more people pass through.

• This phenomenon is essential for understanding how sugars behave in different environments, such as in the body or in food processing.
• The interconversion between \( \alpha\)- and \(\beta\)-anomers demonstrates mutarotation, and it's crucial for chemists to know about this when designing drugs or food additives.

Stereoisomers

Stereoisomers are like the broad umbrella that covers any molecules which have the same molecular formula and sequence of bonded atoms, but that differ in the three-dimensional arrangement of the atoms.

It's as if you had a set of building blocks that could be put together in different ways to make different structures. All stereoisomers fit the same overall pattern, but the specific layout of the blocks can vary.

There are two broad categories: enantiomers, which are non-superimposable mirror images, and diastereomers, which are not mirror images. Both epimers and anomers are types of diastereomers.

• When it comes to glucose, for example, \( \alpha\)-D-Glucopyranose and \( \beta\)-D-Glucopyranose are stereoisomers because they have the same formula but differ in the orientation around the anomeric carbon.
• Understanding the subtleties between different stereoisomers helps in fields like pharmacology, where the shape of a molecule can determine whether a drug will be effective or not.