Structure of Glucose and Fructose

Edited By Team Careers360 | Updated on Jul 02, 2025 04:54 PM IST

Glucose is an Aldo-hexose (monosaccharide with 6 C atoms and an aldehyde group) with a chemical formula C₆H₁₂O₆. The natural form of glucose, i.e., D- glucose is also known as dextrose. It can exist in a linear form or, a pyranose form (5 C atoms with an O atom in ring). Glucose is an aldohexose monosaccharide with a ubiquitous nature that acts as the main substrate in glycolysis in living tissues.

This Story also Contains

Glucose
Properties of Glucose
Glucose and fructose formula
Structure of glucose and fructose
Fructose structural formula
Draw the pyranose structure of glucose
Types of glucose
Preparation of glucose from starch

In this article we under the concept of glucose and fructose which is cover in the Biomolecules of Class 12. This concept is important for board exams and Joint Entrance Examination (JEE Main) and National Eligibility Entrance Test (NEET) and other such entrance exams.

Glucose

Glucose is a monosaccharide present in living cells that is used as a source of energy. Glucose is the main product of photosynthesis and is utilized during cellular respiration in both prokaryotic and eukaryotic individuals.

Types of Monosaccharide

Properties of Glucose

C₆H₁₂O₆	Glucose
Molecular Weight/ Molar Mass	180.16 g/mol
Density	1.54 g/cm³
Melting Point	146 °C
Simple sugar	Monosaccharide
Glucose boiling point	527.1±50.0 °C at 760 mmHg

Glucose and fructose formula

Chemical formula or structural formula of glucose is C₆H₁₂O₆.The chemical formula or structural formula of fructose is also C₆H₁₂O₆. Though glucose and fructose have similar chemical formulas, they differ from each other structurally and stereochemically. And causes differences in molecules despite of sharing the same atoms in the same proportion. Better to say, they are isomers to each other or isomeric monosaccharides.

Also read -

D-glucose formula

D-glucose basically means dextrorotatory (meaning that as an optical isomer when placed inside a polarimeter; that rotates the plane of polarized light to the right and also an origin for the D designation) glucose. This is often termed as dextrose. it is one of the stereoisomers of glucose and is the one that is biologically active. It occurs in plants as a major product of photosynthesis. In animals and fungi, it is the result of the breakdown of glycogen via glycolysis.

Structure of Glucose

D and L glucose

D and L fructose

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Steps are given to Draw the Open Chain Structure (an acyclic form of glucose) of a Glucose Molecule:

Step 1: 6 carbon atoms are drawn at first.

Step 2: the arms for all the carbon atoms excluding the first one are extended.

Step 3: thereafter, hydrogen-to-carbon bonds are drawn such that four are on one side and the remaining one on the other side.

Step 4: The remaining spaces should be filled with a hydroxyl group. (Important – transpose

(OH) to —> (HO) for the left side to show that the oxygen is bonded to carbon)

Step 5: the ends of the chain should be completed with two single-bonded hydrogen bonds and one double-bonded carbon.

D-Glucose and L-Glucose structure

Fructose structural formula

The chemical or structural formula of Fructose is as same as that of glucose, i.e., C₆H₁₂O₆. But they are stereogenically different from each other hence, isomers to each other. Open chain structure of fructose (fructose linear structure). Fructose is a polyhydroxyketone having 6 carbon atoms within it.

D-Fructose and L-Fructose Structure

Cyclic structure of fructose

Crystalline fructose implements a cyclic 6-membered structure, termed β-D-fructopyranose. This is to stabilize its hemiketal and internal hydrogen bonding within it.

Cyclic structure of Fructose

Cyclic structure of glucose

Glucose has 6 carbon atoms and an aldehyde group within it. hence is an aldohexose. Here, the hydroxyl group of the 5th carbon of chain glucose is added to the aldehyde group of the same glucose molecule resulting in the formation of a cyclic hemiacetal. A pyran ring is created hence, the structure is a pyranose structure. The atoms present within the ring then arrange themselves in space to minimize the amount of angle strain on each of the covalent bonds. The glucose molecule will attain its most stable configuration when all the carbon atoms of the ring can arrange themselves so that their bond angles are approximately 109.5.

This type of projection is called Haworth projection of glucose or Haworth structure of glucose. The single-ring structure of glucose indicates that it is a monosaccharide. Acetals are more prone to basic solutions and nucleophilic attack. Hence, Bending, followed by a rotation of the 4th and 5th carbon bond, of the glucose chain brings the C5-hydroxyl group and the aldehyde groups nearer to each other resulting in the formation of a hemiacetal structure containing a six-membered ring.

hemiacetal structure containing a six-membered ring.

At equilibrium, the β anomer of D-glucose predominates over the alpha anomer, as the hydroxyl group of the anomeric carbon is in the more stable position (equatorial position) of the more stable chair conformation. In alpha-D-glucose, the -OH group on the anomeric carbon is in the axial position of the chair conformation which is the least stable.

beta anomer predominates over the alpha anomer in chair conformer

Furanose structure of glucose

When the open-chain form of fructose cyclizes to form a five-membered ring that is called the furanose structure. when the C-5 hydroxyl group attacks the C-2 ketone of the same molecule resulting in the formation of an intramolecular hemiketal. Glucose consists of a 6-membered ring, while fructose consists of a 5-membered ring. Hence, The resulting rings are termed furanose (5 members) or pyranose (6 members) respectively based on their similarity to furan and pyran moiety.

Furanose structure of glucose

Draw the pyranose structure of glucose

Pyranose is a common term to indicate all the saccharides having a chemical structure that includes a 6-membered ring consisting of five carbon atoms and one oxygen atom within it (pyran moiety should be there). There may be other carbons attached externally to the ring. The 6-membered cyclic structure of glucose is termed a pyranose structure (α or β), in similarity with pyran. Glucose is a six-carbon molecule having an aldehyde functional group which leads to the intramolecular attraction between the carbons and the oxygen atom present in the hydroxyl group of the aldehyde functional group of the same molecule which forces these linear molecules to cyclize into rings. There are a total of 38 conformation structures of this type of pyranose ring. They are 2 chair forms, 6 boat forms, 6 skew boat forms, 12 half-chair forms, and 12 envelopes forms.

pyranose and furanose of glucose

Sugars usually exist in an equilibrium between their cyclic and acyclic form and this phenomenon is called “ring-chain tautomerism”.

The 6 membered ring is referred to be the “pyranose” and the five-membered ring is “furanose”.

6-membered ring closure generates a stereogenic carbon (chiral carbon) which is called anomeric carbon that leads to the formation of two diastereomers, preferably known as anomers of glucose. They are alpha-D-glucose pyranose; beta-D- glucose pyranose and alpha-D-glucose furanose; Beta-D-glucose furanose

α and β pyranose formation

Glucose Fischer projection (d glucose Fischer projection/ Fischer projection formula of glucose)

Fischer projections depict the structure of sugars in their open-chain form. In this projection technique, the interlinking of the carbon atoms of the sugar molecule is done using solid lines while the interlinking of the C-O and C-H bonds is done horizontally.

Fructose Fischer projection

Fisher projections depict the structure of fructose contains a keto group at C-2 and the six carbon atoms are arranged in a vertical line whereas the hydrogen and -OH groups are arranged horizontally.

Fisher Projection of Fructose

Haworth structure of fructose

The Fischer projection of the fructose can be converted into the cyclic structure. Like glucose, fructose has a cyclic structure by intramolecular cyclization and results in the formation of alpha and beta anomers.

haworth projection of fructose leads to formation of alpha and beta anomer

Types of glucose

In Fischer projection, there are two types which are diastereomers to each other. They are:

types of glucose in fischer projection

In Haworth projection, there are two types which are anomers to each other. They are:

anomers of glucose in Haworth projection

Preparation of glucose from starch

glucose can be obtained as a major product by hydrolysis of starch, at 393 K temperature and 2-3 atm pressure in the presence of dilute sulphuric acid.

Preparation of Glucose

Excess sulphuric acid, present in the reaction mixture, is neutralized by adding chalk powder.
Activated charcoal is used to remove colored impurities.
The resulting solution is then cooled and crystalline glucose is gradually formed which is removed by filtration.

How to make glucose

Glucose is mainly produced by plants and most algae during photosynthesis using soil water and atmospheric carbon dioxide in the presence of sunlight. The reaction involved in the process:

6CO₂ + 6H₂O + energy→ C₆H₁₂O₆ + 6O₂

Also, students can refer to,

Identification of Glucose

A few common tests for the identification of glucose are- Fehling's Test, Benedict's Test, and Barfoed's Test.

Fehling's Test: in this test, Fehling's Solution (deep blue colored solution results when Fehling 1 and Fehling 2 solutions are mixed) is used to identify the presence of reducing sugars and aldehydes.
Benedict’s reagent or Benedict’s solution is used to test the presence of reducing sugars. In this test, a glucose solution is heated with Benedict’s solution, and the change in color. It gives positive results for glucose but not for starch.
Barford’s test was performed to detect the presence of monosaccharides hence, sugar. In this test copper(II) acetate gets reduced to copper(I) oxide (Cu₂O) in the presence of aldehyde (aldose sugar) which forms a characteristic brick-red precipitate.

RCHO + 2Cu²⁺ + 2H₂O → RCOOH + Cu₂O↓ (brick red) + 4H⁺

Also, check-

NCERT Exemplar Class 11th Chemistry Solutions	NCERT Notes Class 11th Chemistry
NCERT Exemplar Class 12th Chemistry Solutions	NCERT Notes Class 12th Chemistry
NCERT Exemplar Solutions for All Subjects	NCERT Notes For All Subjects

Frequently Asked Questions (FAQs)

1. What is glucose made of?

Glucose is made of a six membered cyclic ring made of 5 carbon and one oxygen (pyran ring) and externally added oner carbon containing hydroxyl group.

2. Is glucose sugar?

Yes, glucose and fructose belong to class of sugars. Termed as aldohexose and aldopentose sugar respectively

3. Glucose is which type of sugar?

Glucose is an aldohexose type of sugar

4. Are glucose and fructose isomers?

Yes, glucose and fructose have the same chemical formula but they differ geometrically. Hence, they are isomers.

5. Why glucose is called dextrose?

glucose is called dextrose as it is dextrorotatory. It rotates the plane polarized light to the right side.

6. What is D glucose?

Dextrorotatory glucose is called D-glucose. It is the stereoisomers of glucose.

7. What is the chemical formula for glucose?

The chemical formula for glucose is C₆H₁₂O₆. It is a hexose sugar, meaning it consists of six carbon atoms.

8. What is the chemical formula for fructose?

The chemical formula for fructose is also C₆H₁₂O₆. Like glucose, fructose is a hexose sugar, but it has a different structure.

9. What are the structural differences between glucose and fructose?

The main structural difference between glucose and fructose lies in the arrangement of their atoms. Glucose has an aldehyde group (-CHO) and is classified as an aldohexose. It has a six-membered ring (pyranose form) when in solution. In contrast, fructose has a ketone group (C=O) and is classified as a ketohexose. It typically forms a five-membered ring (furanose form) in solution.

10. Are glucose and fructose isomers?

Yes, glucose and fructose are structural isomers, meaning they have the same molecular formula (C₆H₁₂O₆) but differ in the arrangement of their atoms.

11. Can glucose and fructose be found in the same foods?

Yes, glucose and fructose can be found in the same foods. For example, table sugar (sucrose) is composed of one glucose molecule and one fructose molecule, and many fruits contain both sugars.

12. What is the importance of the hemiacetal and hemiketal formations in glucose and fructose?

Hemiacetal formation in glucose and hemiketal formation in fructose occur when the carbonyl group reacts with a hydroxyl group to form a cyclic structure. This process is crucial for the stability of these sugars in solution and affects their reactivity in biological systems.

13. What is the importance of the cyclic structure of glucose and fructose in biochemistry?

The cyclic structures of glucose and fructose are crucial in biochemistry as they affect how these sugars interact with enzymes, form glycosidic bonds, and participate in metabolic pathways. The ring structure also contributes to their stability and solubility in aqueous environments.

14. How do glucose and fructose participate in glycosidic bond formation?

Both glucose and fructose can form glycosidic bonds through their anomeric carbon. Glucose typically forms α-1,4 and α-1,6 glycosidic bonds in starch, while fructose forms β-2,1 bonds in fructans. These bonds are crucial in forming complex carbohydrates.

15. What is the role of glucose and fructose in the formation of glycosidic bonds?

Glucose and fructose can form glycosidic bonds through their anomeric carbon atoms. These bonds are crucial in forming disaccharides (like sucrose), oligosaccharides, and polysaccharides. The type of glycosidic bond (α or β) depends on the orientation of the hydroxyl group at the anomeric carbon.

16. How does the structure of glucose and fructose affect their reactivity in biochemical reactions?

The carbonyl group (aldehyde in glucose, ketone in fructose) and the arrangement of hydroxyl groups determine the reactivity of these sugars. For example, the aldehyde group of glucose makes it more reactive in certain oxidation reactions, while the ketone group of fructose affects its metabolism in the liver.

17. How do glucose and fructose contribute to the sweetness of fruits?

Both glucose and fructose contribute to fruit sweetness, but fructose plays a more significant role due to its higher sweetness intensity. The ratio of glucose to fructose varies among different fruits, affecting their overall sweetness and flavor profile.

18. How do glucose and fructose contribute to the formation of advanced glycation end products (AGEs)?

Both glucose and fructose can react non-enzymatically with proteins to form AGEs, but fructose does so at a much faster rate. This process, known as glycation, can lead to tissue damage and is associated with aging and various diseases, particularly in diabetics.

19. What is the importance of the C1 position in glucose and the C2 position in fructose?

In glucose, C1 is the aldehyde carbon and becomes the anomeric carbon in the cyclic form. In fructose, C2 is the ketone carbon and becomes the anomeric carbon. These positions are crucial for the formation of glycosidic bonds and determine many of the chemical properties of these sugars.

20. How does the structure of glucose and fructose affect their metabolism in the human body?

The structural differences between glucose and fructose lead to different metabolic pathways. Glucose can be metabolized by most cells and is regulated by insulin. Fructose is primarily metabolized in the liver, bypasses certain regulatory steps, and can lead to increased lipid production when consumed in excess.

21. What is the importance of the open-chain form of glucose and fructose?

Although glucose and fructose exist predominantly in their cyclic forms in solution, the open-chain form is crucial for many reactions, including mutarotation and the formation of new glycosidic bonds. The open-chain form also allows for the interconversion between these sugars in some metabolic pathways.

22. What is the significance of the Keto-enol tautomerism in glucose and fructose?

Keto-enol tautomerism allows for the interconversion between the aldehyde form of glucose and the ketone form of fructose through an enol intermediate. This process is important in understanding the reactivity of these sugars and their ability to isomerize under certain conditions.

23. How do glucose and fructose contribute to the formation of honey's properties?

Honey is primarily composed of glucose and fructose. The high concentration of these sugars contributes to honey's sweetness, viscosity, and antimicrobial properties. The slightly higher proportion of fructose in many types of honey contributes to its tendency to remain liquid (resist crystallization).

24. How does the structure of glucose and fructose affect their role in glycogen storage?

Glucose is the primary unit in glycogen, a storage polysaccharide in animals. Its structure allows for efficient packing in α-1,4 and α-1,6 linkages. Fructose must be converted to glucose before it can be incorporated into glycogen, which affects energy storage efficiency when consuming fructose-rich foods.

25. How do glucose and fructose differ in their ability to form Schiff bases with amino acids?

Both glucose and fructose can form Schiff bases with amino groups of proteins, but fructose does so more readily. This reactivity is important in the formation of advanced glycation end products (AGEs) and affects protein function and tissue damage in conditions like diabetes.

26. How does the structure of glucose and fructose affect their role in osmotic diarrhea?

When poorly absorbed, both glucose and fructose can cause osmotic diarrhea by drawing water into the intestinal lumen. Fructose is more likely to cause this issue in some individuals due to limited absorption capacity, especially when consumed in large amounts or in the absence of glucose.

27. How do glucose and fructose contribute to the Lobry de Bruyn-van Ekenstein transformation?

This transformation involves the interconversion of aldoses and ketoses in alkaline solution. Glucose (an aldose) can be converted to fructose (a ketose) through this process, which involves enolization. This reaction is important in understanding sugar chemistry and some food processing reactions.

28. How does the structure of glucose and fructose affect their role in glycolysis?

Glucose enters glycolysis directly and is phosphorylated at C6. Fructose, when entering glycolysis, is first phosphorylated to fructose-6-phosphate, which is an intermediate in the glucose pathway. The structural differences affect the enzymes involved and the energy required for their initial metabolism.

29. How does the structure of glucose and fructose affect their role in fermentation processes?

The structure of these sugars affects how they are utilized by microorganisms in fermentation. Glucose is often the preferred substrate for many fermentative organisms. Fructose can also be fermented but may require different enzymatic pathways, affecting the efficiency and products of fermentation.

30. What is the importance of the anomeric carbon in the glycosylation of proteins?

The anomeric carbon of glucose and fructose is crucial in glycosylation, the process of attaching sugars to proteins. The configuration (α or β) at this carbon determines the type of glycosidic linkage formed, which affects the structure and function of glycoproteins in biological systems.

31. How do glucose and fructose participate in non-enzymatic browning reactions?

Both sugars can participate in non-enzymatic browning reactions, such as caramelization and the Maillard reaction. Fructose, being more reactive, often leads to faster browning. These reactions are important in food chemistry, affecting flavor, color, and nutritional properties of cooked and processed foods.

32. How does the body metabolize glucose differently from fructose?

Glucose is metabolized in most cells of the body and is the primary energy source. It stimulates insulin release and is regulated by insulin. Fructose, on the other hand, is primarily metabolized in the liver, doesn't stimulate insulin release, and its metabolism can lead to increased lipid production.

33. What is the role of glucose and fructose in the formation of high fructose corn syrup (HFCS)?

HFCS is produced by enzymatically converting some of the glucose in corn syrup to fructose. The resulting mixture typically contains about 55% fructose and 45% glucose, making it sweeter than regular corn syrup. This process takes advantage of the higher sweetness of fructose compared to glucose.

34. What is the role of glucose and fructose in the formation of caramel?

Both glucose and fructose participate in caramelization, a complex process involving the breakdown and recombination of sugar molecules when heated. Fructose caramelizes at a lower temperature than glucose, contributing to differences in flavor and color development in caramel products.

35. What is the significance of the glycosidic bond angle in glucose and fructose polymers?

The angle of the glycosidic bond affects the overall shape and properties of polysaccharides. In glucose polymers like starch, the α-1,4 bonds create helical structures, while in cellulose, β-1,4 bonds create linear chains. Fructose polymers (fructans) with β-2,1 bonds form different structures with unique properties.

36. What is the role of glucose and fructose in the production of high-intensity sweeteners?

While glucose and fructose themselves are not high-intensity sweeteners, they serve as starting materials for producing some artificial sweeteners. For example, sucralose is derived from sucrose (a disaccharide of glucose and fructose), and some sugar alcohols are produced by reducing these monosaccharides.

37. Why are glucose and fructose considered reducing sugars?

Glucose and fructose are reducing sugars because they have a free aldehyde or ketone group that can be oxidized, allowing them to act as reducing agents in chemical reactions. This property is important in many biochemical processes and analytical tests.

38. How does the sweetness of glucose compare to fructose?

Fructose is significantly sweeter than glucose. On a relative sweetness scale where sucrose is 100, fructose rates about 173, while glucose rates about 74. This difference in sweetness affects their use in food products and metabolism in the body.

39. How do glucose and fructose participate in the Maillard reaction?

Both glucose and fructose can participate in the Maillard reaction, a complex series of reactions between reducing sugars and amino acids that produce brown pigments and flavor compounds. Fructose tends to react faster in this process, leading to more rapid browning and flavor development.

40. How do glucose and fructose differ in their ability to form crystalline structures?

Glucose tends to form crystals more readily than fructose due to its more symmetrical structure. Fructose is more hygroscopic (attracts water) and tends to form syrups rather than crystals under normal conditions. This property affects their use in food products and storage stability.

41. What is the role of glucose and fructose in the formation of dental caries?

Both glucose and fructose can be fermented by oral bacteria to produce acids that demineralize tooth enamel, leading to dental caries. Fructose is often considered more cariogenic than glucose due to its ability to form extracellular polysaccharides that adhere to teeth.

42. What is the basic structure of glucose and fructose?

Glucose and fructose are both monosaccharides with the molecular formula C6H12O6. However, their structures differ. Glucose is an aldohexose with an aldehyde group at C1, while fructose is a ketohexose with a ketone group at C2. Both have multiple hydroxyl (-OH) groups attached to their carbon chains.

43. How do glucose and fructose differ in their ring structures?

Glucose typically forms a six-membered ring (pyranose) structure, while fructose usually forms a five-membered ring (furanose) structure. This difference arises from the position of their carbonyl groups and affects their reactivity and properties.

44. How does the structure of glucose and fructose affect their ability to form hydrogen bonds?

Both glucose and fructose have multiple hydroxyl groups that can form hydrogen bonds with water and other molecules. The specific arrangement of these groups in their cyclic structures influences their hydrogen bonding capacity, affecting properties like solubility and interaction with biological molecules.

45. How does the structure of glucose and fructose affect their solubility in water?

Both glucose and fructose are highly soluble in water due to their multiple hydroxyl groups, which can form hydrogen bonds with water molecules. However, fructose is slightly more soluble than glucose because its ketone group can form stronger hydrogen bonds than glucose's aldehyde group.

46. What is the significance of the Fischer projection in representing glucose and fructose?

The Fischer projection is a two-dimensional representation of three-dimensional sugar molecules. It's particularly useful for showing the stereochemistry of glucose and fructose, including the arrangement of hydroxyl groups and the position of the carbonyl group, which distinguishes these sugars.

47. What is mutarotation, and how does it apply to glucose and fructose?

Mutarotation is the change in optical rotation that occurs when a sugar converts between its α and β anomeric forms in solution. Both glucose and fructose undergo mutarotation, reaching an equilibrium mixture of their α and β forms over time.

48. What is the significance of the anomeric carbon in glucose and fructose?

The anomeric carbon is the carbon atom that was originally the carbonyl carbon in the open-chain form of the sugar. In glucose, it's C1, while in fructose, it's C2. This carbon can form two different configurations (α and β) when the ring closes, leading to different properties and reactivity.

49. What is the difference between D-glucose and L-glucose?

D-glucose and L-glucose are mirror images of each other (enantiomers). D-glucose is the naturally occurring form found in living organisms, while L-glucose is synthetic and not metabolized by the body. The "D" and "L" refer to the configuration of the hydroxyl group on the highest numbered chiral carbon.

50. What is the significance of the anomeric effect in glucose and fructose structures?

The anomeric effect is a stereoelectronic effect that influences the stability of different anomeric forms of sugars. In glucose and fructose, it affects the equilibrium between α and β anomers and plays a role in the conformational preferences of these sugars in solution and when bound to enzymes.

51. How do glucose and fructose differ in their furanose forms?

While both glucose and fructose can form furanose (five-membered ring) structures, fructose more commonly exists in this form. Glucose furanose is less stable and less common than its pyranose form. The furanose form of fructose is important in many biological processes, including the formation of sucrose.

52. What is the significance of the Haworth projection in representing glucose and fructose?

The Haworth projection is a way to represent the cyclic structure of sugars in two dimensions. It clearly shows the orientation of hydroxyl groups and the position of the anomeric carbon, making it useful for understanding the stereochemistry and reactivity of glucose and fructose.

53. What is the significance of the boat and chair conformations in glucose and fructose?

The cyclic forms of glucose and fructose can adopt different conformations, with the chair being the most stable for six-membered rings (like glucose pyranose). These conformations affect the reactivity and binding properties of the sugars to enzymes and other biological molecules.

54. How does the structure of glucose and fructose affect their role in osmotic balance in cells?

As small, soluble molecules, both glucose and fructose contribute to osmotic pressure in cells. Their cyclic structures and ability to form hydrogen bonds with water make them effective osmolytes. In plants, the interconversion between glucose and fructose can affect osmotic balance and water movement.

55. What is the importance of the furanose form of fructose in the structure of sucrose?

In sucrose, fructose exists in its furanose form, linked to glucose through an α-1,β-2 glycosidic bond. This specific structure contributes to sucrose's unique properties, including its sweetness, solubility, and resistance to hydrolysis by certain enzymes.

56. What is the significance of the reducing end in glucose and fructose polymers?

The reducing end of a sugar polymer is the end with a free anomeric carbon capable of reducing other compounds. In glucose polymers like starch, this is typically the C1 end. The reducing end is important in analytical techniques and can participate in various chemical reactions.

57. What is the importance of the axial and equatorial positions of hydroxyl groups in glucose and fructose?

The axial or equatorial position of hydroxyl groups in the cyclic forms of