Q. 13.78 - An Introduction to General, Organic, and Biological Chemistry

Question

Identify the Fischer projection A to D  that matches each of the following: (13.1, 13.3)

a. the L enantiomer of mannose

b. a ketopentose

c. an aldopentose

d. a ketohexose

Step-by-Step Solution

Answer

Part a) The L-enantiomer of aldehydo-mannose is aldehydo-L-mannose. It's an aldehydo-mannose and an L-mannose. It is an aldehydo-D-mannose enantiomer.

Part b) Fructose, psicose, sorbose, and tagatose are examples of ketohexoses, which are six-carbon monosaccharides. The word ketopentose refers to a ketone that comprises five carbon atoms.

Part c)  A pentose with a (potential) aldehyde group at one end. 

Part d)  Ketohexoses are six-carbon monosaccharides, which include fructose, psicose, sorbose, and tagatose.  

Step 1 : Introduction (Part a)

• Emil Fischer invented the Fischer projection, a way of visualizing three-dimensional structures of molecules on a page.
• Horizontal lines represent bonds that are projecting toward the viewer from the plane of the paper.
• While vertical lines represent bonds that are projecting away from the spectator.

Step 2: Identify the Fischer projection (Part a)

We know that mannose is an aldohexose and there is only one aldohexose in the Fischer projection from A to D.

The structure B belongs to the L enantiomer of mannose because it has all opposite stereogenic centers than Dmannose.

Step 3 b: Introduction

• Emil Fischer invented the Fischer projection, a way of visualizing three-dimensional structures of molecules on a page.
• Horizontal lines represent bonds that are projecting toward the viewer from the plane of the paper.
• While vertical lines represent bonds that are projecting away from the spectator.

Step 4 b: Identify the Fischer projection

• Ketopentose is a carbohydrate that has five carbons and a ketone group, and between Fischer projection from A to $D$ there is only one structure that has five carbons and a ketone group.
• Fischer projection C is a ketopentose.
  

Step 5 c Introduction

• Emil Fischer invented the Fischer projection, a way of visualizing three-dimensional structures of molecules on a page.
• Horizontal lines represent bonds that are projecting toward the viewer from the plane of the paper.
• While vertical lines represent bonds that are projecting away from the spectator.

Step 6 c : Identify the Fischer projection

• Aldopentose are carbohydrates with five carbons and an aldehyde group, and between the structures from A to D, there are two structures with an aldehyde group but only one with an aldehyde group and five carbons.
• Fischer projection $\mathbf{A}$ is an aldopentose.

Step 7 d: Introduction

• Emil Fischer invented the Fischer projection, a way of visualizing three-dimensional structures of molecules on a page.
• Horizontal lines represent bonds that are projecting toward the viewer from the plane of the paper.
• While vertical lines represent bonds that are projecting away from the spectator.

Step 8 d: Identify the Fischer projection

• Ketohexose is a carbohydrate that has six carbons and a ketone group, and between Fischer projection from A to D there is only one structure that has six carbons and a ketone group.
• Fischer projection D is a ketohexose.