Q.39 Which of the following is(are) CORRECT?
(A) Both glucose and fructose have the same molecular formula
(B) The positions of the oxygen and carbon differ in the structures of glucose and fructose
(C) Both glucose and fructose have the same physical properties
(D) Both glucose and fructose are monosaccharides
Correct Options: (A), (B), and (D)
Glucose and fructose share key chemical similarities as monosaccharides but differ in structure and properties. Options (A), (B), and (D) accurately describe these relationships, while (C) does not due to distinct physical traits.
Option Analysis
Option (A): Both glucose and fructose have the molecular formula C₆H₁₂O₆, confirming they contain identical numbers of carbon, hydrogen, and oxygen atoms. This makes them isomers despite structural variations.
Option (B): Glucose features an aldehyde group (-CHO) at carbon 1 (aldohexose), while fructose has a ketone group (C=O) at carbon 2 (ketohexose), altering oxygen and carbon positions. These differences extend to cyclic forms: glucose forms a six-membered pyranose ring, fructose a five-membered furanose ring.
Option (C): Glucose and fructose exhibit different physical properties, including melting points (glucose ~146°C, fructose ~103°C), density (glucose 1.54 g/cm³, fructose 1.69 g/cm³), solubility (fructose higher), and sweetness (fructose ~1.7 times sweeter). These variations arise from their structural isomerism.
Option (D): Both qualify as monosaccharides, the simplest carbohydrates that cannot hydrolyze further into simpler sugars.
Glucose and fructose represent fundamental monosaccharides critical for CSIR NET Life Sciences exams, sharing the same molecular formula yet differing in key structures and properties. This detailed breakdown covers their molecular formula, oxygen and carbon positioning, physical properties, and classification as monosaccharides, aiding competitive exam preparation.
Molecular Formula Similarity
Both glucose and fructose possess the molecular formula C₆H₁₂O₆, classifying them as hexose isomers with identical atomic composition. This equality underpins their roles in energy metabolism despite structural distinctions.
Structural Differences
Glucose, an aldohexose, positions its aldehyde oxygen at carbon 1, while fructose, a ketohexose, locates its ketone oxygen at carbon 2, shifting carbon-oxygen arrangements. In solution, glucose adopts a pyranose ring, fructose a furanose ring, influencing reactivity and biological function.
Physical Properties Comparison
| Property | Glucose | Fructose |
|---|---|---|
| Melting Point | ~146°C | ~103°C |
| Density | 1.54 g/cm³ | 1.69 g/cm³ |
| Solubility | High in water | Higher in water |
| Sweetness | Sweet | 1.7x sweeter |
These disparities confirm glucose and fructose lack identical physical properties.
Monosaccharide Classification
As monosaccharides, both serve as building blocks for disaccharides like sucrose and provide rapid cellular energy without hydrolysis. Their reducing sugar nature supports biochemical tests in lab settings.
