What structural relationship do D-glucose and D-fructose share?

D-glucose and D-fructose are classified as structural isomers, which means they share the same molecular formula (C6H12O6) but differ in the arrangement of their atoms. Specifically, D-glucose is an aldohexose, containing an aldehyde group at one end of its six-carbon chain, while D-fructose is a ketohexose, featuring a ketone group at the second carbon. This difference in functional groups and connectivity of the carbon skeleton exemplifies the concept of structural isomerism.

Understanding this relationship is fundamental because it highlights how isomers can have significantly different chemical properties and functions despite sharing identical molecular formulas. This concept is relevant in biochemistry, where different sugars can play various roles in metabolism and energy production.