Question

Classify the sugars as either aldoses or ketoses. A Fischer projection with a six carbon backbone. Carbon one is an aldehyde and carbon six is part of the group C H 2 O H. Carbons two and three have an hydroxide group on the left, and carbons four and five have an hydroxide group on the right. A Fischer projection of a six carbon backbone. Carbons one and six are part of a C H 2 O H group. Carbon two is attached to a ketone, carbons three and four have a hydroxide group on the left, and carbon five has a hydroxide group on the right. A Fischer projection with a five carbon backbone. Carbon one is an aldehyde, carbon five is part of the group C H 2 O H, and carbons two through four have an hydroxide group on the right. A Fischer projection with a three carbon backbone. Carbon one is an aldehyde, carbon three contains the group C H 2 O H, and carbon two has a hydroxide group on the right. A Fischer projection with a five carbon backbone. Carbons one and five are part of a C H 2 O H group. Carbon two is attached to a ketone and carbons three and four have a hydroxide group on the right. A Fischer projection of a four carbon backbone. Carbons one and four are part of a C H 2 O H group. Carbon two is attached to a ketone and carbon three has a hydroxide group on the right. Answer Bank

Answer 1

Answer AND Explanation: Carbohydrates or sugars have three classes:

1. Monossaccharides: made from a single polyhydroxy aldehyde or ketone unit;
2. Oligosaccharides: formed by short chains of monossacharides united by glycosidic linkage;
3. Polysaccharides: consist of a long chain of monossaccharides;

Monossaccharides are formed by a chain of unbranched carbon, all bonded  by single bonds, except for a carbon that is double-bonded by an oxygen. This bond form a carbonyl group.

If the carbonyl is at an end of the chain, the carbon is aldehyde and the molecule is called aldose. If the group is in any other position, it is a ketone and is called ketose

So analysing each projection:

1) Carbon one is a aldehyde, which means is a carbonyl and there are no other carbons forming that bond, so it's a ALDOSE

2) Carbon two is attached to a ketone and other carbons aren't, so it's a KETOSE.

3) Carbon one is aldehyde, so it's ALDOSE

4) Carbon one is aldehyde, so ALDOSE

5) Carbon two is attached to ketone, so KETOSE

6) Carbon two attached to a ketone, so KETOSE