What is the essential difference between `alpha` - and - `beta` - forms of glucose ?

Options

A. isomers of D(+) glucose and L(-) glucose respectively
B. diastereomers of glucose
C. anomers of glucose
D. isomers which differ in the configuration of C-2

Answer

To explain the essential difference between the alpha and beta forms of glucose, we can follow these steps:

### Step 1: Understanding the Structure of Glucose
Glucose is a six-carbon sugar (hexose) that can exist in two cyclic forms: alpha (α) and beta (β). These forms arise due to the arrangement of the hydroxyl (OH) group attached to the anomeric carbon (the first carbon in the ring structure).

### Step 2: Drawing the Structures
1. **Alpha (α) Glucose**: In the α-glucose structure, the hydroxyl group (-OH) on the anomeric carbon (C1) is positioned **below** the plane of the ring.
- Structure:
```
CH2OH
|
H-C-OH
|
HO-C-H
|
H-C-H
|
H-C-OH
|
H
```

2. **Beta (β) Glucose**: In the β-glucose structure, the hydroxyl group (-OH) on the anomeric carbon (C1) is positioned **above** the plane of the ring.
- Structure:
```
CH2OH
|
H-C-OH
|
HO-C-H
|
H-C-H
|
H-C-OH
|
H
```

### Step 3: Identifying the Anomeric Carbon
The anomeric carbon is the first carbon in the cyclic structure of glucose. The difference between the two forms lies in the orientation of the hydroxyl group attached to this carbon.

### Step 4: Conclusion
The essential difference between the alpha and beta forms of glucose is the position of the hydroxyl group on the anomeric carbon:
- In **α-glucose**, the -OH group is **below** the plane of the ring.
- In **β-glucose**, the -OH group is **above** the plane of the ring.

### Final Answer
The essential difference between alpha and beta forms of glucose is the position of the hydroxyl group (-OH) on the anomeric carbon: it is below the plane in α-glucose and above the plane in β-glucose.

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