Question

Monosaccharides can be categorized in terms of the number of carbon atoms (pentoses have five carbons and hexoses have six carbons) and according to whether they contain an aldehyde (aldo- prefix, as in aldopentose) or ketone group (keto- prefix, as in ketopentose). Classify glucose and fructose in this way.

Short answer

Glucose is classified as an aldohexose, as it contains six carbon atoms (hexose) and has an aldehyde functional group. Fructose is classified as a ketohexose, as it also contains six carbon atoms (hexose) but has a ketone functional group instead.

Step-by-step solution

Determine the structural formulas of glucose and fructose

To classify glucose and fructose, we need to identify their structural formulas. Glucose has the molecular formula C6H12O6 and its structure is as follows: \[CHO(CHOH)_4CH_2OH\] Fructose also has the molecular formula C6H12O6, but its structure is different: \[CH_2OH(CHOH)_3COCH_2OH\]

Identify the number of carbon atoms in glucose and fructose

As we can see from their structural formulas, both glucose and fructose have six carbon atoms. Therefore, they belong to the hexose category.

Identify the functional group in glucose and fructose

Now, let's determine whether glucose and fructose have an aldehyde or ketone functional group. In glucose, the first carbon atom (from the left) is bound to an oxygen atom by a double bond, which is characteristic of the aldehyde group (CHO). Therefore, glucose has an aldehyde functional group. In fructose, the second carbon atom (from the left) is bound to an oxygen atom by a double bond, which is characteristic of the ketone group (C=O). Therefore, fructose has a ketone functional group.

Classify glucose and fructose

Based on our analysis, glucose is an aldohexose because it has six carbon atoms and contains an aldehyde functional group. Fructose is a ketohexose because it has six carbon atoms and contains a ketone functional group.