Chapter 13: Problem 50
What are the differences in the Haworth structures of \(\alpha\) -D-glucose and \(\beta\) -D-glucose?
Short Answer
Expert verified
The \(\alpha\) form has the -OH group below the ring, and the \(\beta\) form has the -OH group above the ring at C1.
Step by step solution
01
Identify the Anomeric Carbon
Both \(\alpha\)-D-glucose and \(\beta\)-D-glucose are cyclic structures. Locate the anomeric carbon, which is carbon 1 (C1). In the Haworth projection, this is the carbon directly to the right of the oxygen in the ring.
02
Observe the Hydroxyl Group Position
The difference between \(\alpha\)-D-glucose and \(\beta\)-D-glucose lies in the position of the hydroxyl group (-OH) attached to the anomeric carbon (C1).
03
Hydroxyl Group in \(\alpha\)-D-glucose
In \(\alpha\)-D-glucose, the hydroxyl group on the anomeric carbon is positioned below the plane of the ring (downward). This configuration is often referred to as the 'trans' configuration to the CH2OH group at C5.
04
Hydroxyl Group in \(\beta\)-D-glucose
In \(\beta\)-D-glucose, the hydroxyl group on the anomeric carbon is positioned above the plane of the ring (upward). This configuration is referred to as the 'cis' configuration to the CH2OH group at C5.
05
Summarize the Difference
The primary difference between the Haworth structures of \(\alpha\)-D-glucose and \(\beta\)-D-glucose is the position of the hydroxyl group on the anomeric carbon: below the ring in \(\alpha\)-D-glucose and above the ring in \(\beta\)-D-glucose.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Anomeric Carbon
The anomeric carbon is crucial for distinguishing between different forms of cyclic sugars, such as glucose. In the Haworth projections of glucose, the anomeric carbon is identified as carbon 1 (C1). This carbon is located directly to the right of the oxygen in the ring structure. When glucose transforms from its open-chain form to a cyclic form, the carbonyl carbon (C1) reacts, forming a new chiral center known as the anomeric carbon.
Anomeric carbons can bond in two different ways, leading to the formation of either an \(\alpha\) or \(\beta\) form of the sugar. Remember, C1 transforms into the anomeric carbon in both \(\alpha\)-D-glucose and \(\beta\)-D-glucose. The positioning of the attached -OH group helps us determine whether the glucose molecule is in its alpha or beta form.
Anomeric carbons can bond in two different ways, leading to the formation of either an \(\alpha\) or \(\beta\) form of the sugar. Remember, C1 transforms into the anomeric carbon in both \(\alpha\)-D-glucose and \(\beta\)-D-glucose. The positioning of the attached -OH group helps us determine whether the glucose molecule is in its alpha or beta form.
Hydroxyl Group Position
In cyclic sugars like glucose, the position of the hydroxyl (-OH) group attached to the anomeric carbon plays a key role in defining the molecule's properties. Specifically, the position of this hydroxyl group determines whether we have \(\alpha\)-D-glucose or \(\beta\)-D-glucose.
When examining Haworth projections, focus on the anomeric carbon (C1):
When examining Haworth projections, focus on the anomeric carbon (C1):
- In \(\alpha\)-D-glucose, the hydroxyl group on C1 points downward, below the plane of the ring.
- In \(\beta\)-D-glucose, the hydroxyl group at C1 points upward, above the plane of the ring.
Alpha and Beta Glucose
The designations \(\alpha\)-D-glucose and \(\beta\)-D-glucose refer to the two anomers of D-glucose, differing only in the orientation of the hydroxyl group attached to the anomeric carbon (C1).
The terms 'alpha' and 'beta' denote this difference:
The terms 'alpha' and 'beta' denote this difference:
- \(\alpha\)-D-glucose has the -OH group on the anomeric carbon positioned below the ring plane. This arrangement is also called the 'trans' configuration relative to the CH2OH group on C5.
- \(\beta\)-D-glucose has the -OH group on the anomeric carbon above the ring plane. This is known as the 'cis' configuration relative to the CH2OH group on C5.