Chemical Formula of Glucose
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The formula of glucose, the direct answer is $\ce{C6H12O6}$ — but this same glucose molecule formula is also shared by fructose and galactose, which is exactly why board exams and NEET/JEE ask you to go beyond just the molecular formula. This page, from the Biomolecules chapter, breaks down the chemical formula of glucose at every level — molecular, empirical, structural, and cyclic — so you understand it completely, not just memorise it.
What Is the Chemical Formula of Glucose?
Glucose is a naturally occurring monosaccharide (simple sugar) and the most abundant carbohydrate found in living organisms. The chemical formula of glucose is:
$\ce{C6H12O6}$
This glucose chemical formula tells you that every glucose molecule is built from 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms, bonded together in a specific arrangement. Glucose belongs to the class of compounds called aldohexoses, because it has six carbon atoms (hexose) and an aldehyde functional group (aldo-).
Glucose Molecular Formula: $\ce{C6H12O6}$ Explained
The glucose molecular formula, $\ce{C6H12O6}$, represents the actual number of atoms present in one molecule of glucose — not just their simplest ratio. This distinguishes the molecular formula from the empirical formula (explained below).
Property | Detail |
|---|---|
Molecular formula | $\ce{C6H12O6}$ |
Molar mass | 180.16 g/mol |
Type of carbohydrate | Monosaccharide (aldohexose) |
Functional groups present | 1 aldehyde ($\ce{-CHO}$) + 5 hydroxyl ($\ce{-OH}$) |
IUPAC-style name | D-(+)-Glucose |
Common natural sources | Fruits, honey, grapes, blood (blood sugar) |
Empirical Formula of Glucose
The empirical formula shows the simplest whole-number ratio of atoms in a compound, unlike the molecular formula, which shows the actual count. For glucose:
- Molecular formula: $\ce{C6H12O6}$
- Simplest ratio of C : H : O = 1 : 2 : 1
- Empirical formula of glucose: $\ce{CH2O}$
This is also why carbohydrates as a class were historically named "hydrates of carbon" — the general empirical formula $\ce{Cn(H2O)n}$ matches glucose exactly when n = 6, i.e., $\ce{C6(H2O)6}$ simplifies to $\ce{C6H12O6}$.
Once this molecular-vs-empirical distinction is clear, test your recall with eSaral's NEET Test Series, which includes dedicated Biomolecules mock sections
Structural Formula of Glucose (Open-Chain Form)
The structure of glucose is best understood by first looking at its open-chain form. The Structural formula of glucose in this open-chain arrangement is written as:
While $\ce{C6H12O6}$ is the chemical formula of glucose, it doesn't show how the atoms are connected. The open-chain structural formula of glucose is written as:
$\ce{CH2OH-CHOH-CHOH-CHOH-CHOH-CHO}$
Reading this structure from C-1 to C-6:
- C-1: Aldehyde group ($\ce{-CHO}$) — this is why glucose is classified as an aldose and gives positive tests with Tollens' and Fehling's reagents.
- C-2 to C-5: Each carbon carries one hydroxyl group ($\ce{-OH}$), making glucose a pentahydroxy aldehyde.
- C-6: A terminal $\ce{-CH2OH}$ (primary alcohol) group.
This open-chain form explains why the glucose molecule formula, though written simply as $\ce{C6H12O6}$, actually represents a highly reactive polyhydroxy aldehyde.
Cyclic Structure of Glucose (Pyranose Form)
The open-chain structural formula of glucose explains its reactivity, but the actual structure of glucose in solution is predominantly the ring (pyranose) form. In reality, glucose exists predominantly not in the open-chain form but as a six-membered ring, formed when the $\ce{-OH}$ group on C-5 attacks the aldehyde carbon (C-1) intramolecularly. This ring structure is called the pyranose form, and it explains two experimentally observed puzzles about glucose that the plain open-chain chemical formula of glucose cannot:
- Glucose does not give the characteristic color reaction of aldehydes with Schiff's reagent.
- Glucose exists in two distinct crystalline forms with different optical rotations.This distinction between anomers is a recurring pattern in JEE Main Chapterwise PYQ as well, especially in stereochemistry-linked questions.
Alpha (α) and Beta (β) Glucose
When the ring closes, C-1 becomes a new chiral centre called the anomeric carbon, producing two cyclic isomers:
Form | Position of –OH on C-1 | Specific Rotation |
|---|---|---|
α-D-Glucose | Below the plane of the ring | +112° |
β-D-Glucose | Above the plane of the ring | +18.7° |
Both α and β glucose share the exact same molecular formula, $\ce{C6H12O6}$ — they are anomers, differing only in the spatial arrangement at C-1.
Difference Between Glucose Molecule Formula and Fructose Formula
A very common confusion (and a favourite exam trap) is that glucose and fructose share an identical molecular formula, $\ce{C6H12O6}$, despite being structurally different sugars:
Basis | Glucose | Fructose |
|---|---|---|
Molecular formula | $\ce{C6H12O6}$ | $\ce{C6H12O6}$ |
Type | Aldohexose (aldehyde group) | Ketohexose (ketone group) |
Functional group at C-1/C-2 | $\ce{-CHO}$ at C-1 | $\ce{C=O}$ (ketone) at C-2 |
Ring form | Pyranose (6-membered) | Furanose (5-membered) |
Relationship | — | Functional isomer (isomeric with glucose) |
Because both compounds satisfy the same chemical formula, $\ce{C6H12O6}$, glucose and fructose are classic examples of structural (functional) isomers — a concept frequently tested alongside the glucose formula itself. Practice how this exact confusion is tested with NEET Chapterwise PYQ.
Molecular Formula of Common Hexose Monosaccharides
Monosaccharide | Molecular Formula | Type |
|---|---|---|
Glucose | $\ce{C6H12O6}$ | Aldohexose |
Fructose | $\ce{C6H12O6}$ | Ketohexose |
Galactose | $\ce{C6H12O6}$ | Aldohexose |
Where Does Glucose Fit in the Biomolecules Chapter?
In the Biomolecules chapter of Class 12 Chemistry, glucose is studied as the most important monosaccharide under the broader topic of carbohydrates. Carbohydrates are classified based on their behaviour on hydrolysis:
- Monosaccharides — cannot be hydrolysed further; glucose, fructose, and galactose belong here.
- Oligosaccharides — give 2–10 monosaccharide units on hydrolysis (e.g., sucrose gives glucose + fructose).
- Polysaccharides — give many monosaccharide units on hydrolysis (e.g., starch, cellulose, glycogen — all built from repeating glucose units).
Understanding the chemical formula of glucose deeply — not just as $\ce{C6H12O6}$, but as a pentahydroxy aldehyde that exists in equilibrium between open-chain and cyclic forms — is the foundation for understanding glycosidic bonds, reducing sugars, and polysaccharide structure later in the same chapter. Check the NEET Syllabus to see how much weight Biomolecules carries within the overall NEET Chemistry section.
Mastering the structure of glucose and its Structural formula of glucose alongside the molecular formula gives you the complete picture needed for glycosidic bond and reducing sugar questions in the Biomolecules chapter
Explore More on eSaral (Related Biomolecules & Class 12 Chemistry Resources)
- Master the complete chapter this topic belongs to: Chemistry Class 12 Biomolecules Notes for IIT JEE & NEET →
- Solve exercise-based questions on this exact chapter: NCERT Solutions for Class 12 Chemistry Chapter 14 Biomolecules →
- Quick visual revision before exams: Mind Map for Biomolecules – Class 12, JEE & NEET →
- Practice previous year NEET questions from this chapter: Biomolecules NEET Previous Year Questions & Solutions →
- Get the latest 2026–27 chapter-wise revision notes: CBSE Class 12 Chemistry Revision Notes PDF 2026–27 →
- Download the complete syllabus reference: NCERT Class 12 Chemistry Book – Free PDF
- Practice Biomolecules-based NEET previous year questions: NEET Chapterwise PYQ with Solutions →
Struggling to connect the glucose formula with the rest of the Biomolecules chapter — glycosidic bonds, reducing sugars, and polysaccharides? eSaral's Class 12 Chemistry course, taught by IIT Bombay faculty, breaks every Biomolecules concept into structured, exam-ready tables and diagrams, with a 5-layer doubt-solving system to clear doubts the same day. Start your free eSaral Class 12 Chemistry demo class today →
Frequently Asked Questions
Is the chemical formula of glucose and fructose the same?
Yes, both glucose and fructose share the identical molecular formula $\ce{C6H12O6}$, but they are functional isomers — glucose has an aldehyde group while fructose has a ketone group.
What is the empirical formula of glucose?
The empirical formula of glucose is $\ce{CH2O}$, representing the simplest whole-number ratio of carbon, hydrogen, and oxygen atoms (1:2:1).
What is the molecular formula of glucose?
The molecular formula of glucose is $\ce{C6H12O6}$, which represents the actual number of atoms in one molecule, as opposed to its empirical formula, $\ce{CH2O}$.
What is the chemical formula of glucose?
The chemical formula of glucose is $\ce{C6H12O6}$, meaning each glucose molecule contains 6 carbon, 12 hydrogen, and 6 oxygen atoms.
Why doesn't glucose give a positive test with Schiff's reagent despite having an aldehyde group?
Because glucose exists predominantly in its cyclic pyranose form in solution, where the free aldehyde group is not available to react with Schiff's reagent.
What is D-glucose, and why is it called D-(+)-glucose?
"D" refers to the configuration of the molecule relative to D-glyceraldehyde, and "(+)" indicates that glucose is dextrorotatory, meaning it rotates plane-polarised light to the right.
What is the difference between the open-chain and cyclic formula of glucose?
The open-chain formula shows glucose as a straight-chain pentahydroxy aldehyde, while the cyclic (pyranose) formula shows the six-membered ring formed when the C-5 hydroxyl group reacts with the C-1 aldehyde group.
How many hydroxyl (-OH) groups are present in glucose?
Glucose contains five hydroxyl ($\ce{-OH}$) groups in its open-chain structure, along with one aldehyde ($\ce{-CHO}$) group at C-1.
What is the structure of glucose?
The structure of glucose can be represented in two forms — an open-chain structural formula ($\ce{CH2OH-CHOH-CHOH-CHOH-CHOH-CHO}$) showing an aldehyde group ($\ce{-CHO}$) at C-1 and five hydroxyl ($\ce{-OH}$) groups, and a cyclic pyranose structure formed when the C-5 $\ce{-OH}$ group reacts with the C-1 aldehyde carbon.