Question

As we have seen in Chapter 28, monosaccharides can be drawn in a variety of ways, and in truth, often a mixture of cyclic compounds is present in a solution. Identify each monosaccharide, including its proper D, L designation, draw in a less-than-typical fashion.

(a.)

(b.)

(c.)

(d.)

Short answer

Answer

(a.)

(b.)

(c.)

(d.)

Step-by-step solution

Monosaccharide

Carbohydrates comprising one saccharide unit are termed monosaccharides. They are the simplest sugars and cannot be further reduced into simpler units by hydrolysis.

D, L designation of monosaccharide

D and l designation are a simpler way of representing enantiomers. For a sugar illustrated with the oxidized carbon at the upper position ( aldehyde or ketone):

• D designation is provided to the OH situated at the chiral down centre positioned at the right.
• L designation is provided to the OH situated at the chiral down centre positioned at the left.

Identification of monosaccharides a and b, including its proper D and L designation

The cyclic structure is converted to an acyclic form (Fischer projection) so that the D and L designation can be understood using the acyclic form.

a. The Fischer projection of compound a can be given as:

Fischer projection of compound a

Hence, the given compound has a D designation.

b. The Fischer projection of compound b can be given as:

Fischer projection of compound b

Hence, the given monosaccharide has a D designation.

Identification of monosaccharides c and d

c.) The Fischer projection of compound c can be given as:

Fischer projection of compound c

Hence, the given monosaccharide has a D designation.

d. The Fischer projection of compound d can be given as:

Fischer projection of compound d

Hence, the given monosaccharide has an L designation.