Hydrogen Bonding

Hydrogen Bonding

Edited By Shivani Poonia | Updated on Jul 02, 2025 06:20 PM IST

Hydrogen bonding has immense effects on the features of substances. It is a shared interaction of a hydrogen atom that is covalently bonded to an electronegative atom, for instance, oxygen, nitrogen, or fluorine, with another electronegative atom. It is not a real chemical bond at all but rather a specially strong kind of intricate dipole-dipole attraction. Because of hydrogen bonds, various structures of water, proteins, and nucleic acids like DNA also show features of stability.

This Story also Contains

Hydrogen Bonding
Formation of Hydrogen Bond
Types of Hydrogen Bonding
Relevance and Applications of Hydrogen Bonding
Some Solved Examples
Summary

Hydrogen Bonding

Hydrogen bonds are strong forces that occur when a hydrogen atom bonded to an electronegative atom approaches a nearby electronegative atom such as O, N, F, etc. Greater the electronegativity of the atom will increase in hydrogen-bond strength. The hydrogen bond is a stronger intermolecular force, but it is weaker than a covalent or an ionic bond. Hydrogen bonds are responsible for holding together DNA, proteins, and other macromolecules.

Formation of Hydrogen Bond

A hydrogen bond is an electromagnetic attraction that occurs between a partially positively charged hydrogen atom attached to a highly electronegative atom and another nearby electronegative atom. A hydrogen bond is a type of dipole-dipole interaction; it is not a true chemical bond. This hydrogen bond attraction can occur between different molecules (intermolecularly) or within different parts of a single molecule (intramolecularly).

Types of Hydrogen Bonding

There are two types of hydrogen bonding, i.e:

Intermolecular Hydrogen Bonding: Intermolecular hydrogen bonding occurs when the H-atom of one molecule and an electronegative atom of another molecule are close to each other. For example, hydrogen bonds between the molecules of hydrogen fluoride. Intermolecular hydrogen bonding results in the association of molecules. Thus, it increases the melting point, boiling point, solubility, etc.
Intramolecular Hydrogen Bonding: Intramolecular hydrogen bonding occurs when the hydrogen atom and an electronegative atom of the same molecule are close to each other. Intramolecular hydrogen bonding results in the cyclization of the molecules and prevents their association. Thus, the properties of these compounds like melting point, boiling point, etc. are usually low. For example, intramolecular hydrogen bonding is present in molecules such as o-nitrophenol, o-nitrobenzoic acid, etc..

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Relevance and Applications of Hydrogen Bonding

Hydrogen bonding relevance has gone on to influence many real applications and academic fields.

1. Biological Importance: Of biological significance is the role of these bonds in ensuring that macromolecules remain stable throughout their functional processes. For instance, hydrogen bonds hold the two strands of DNA in a double helix configuration through the hydrogen bonding between complementary base pairs such as adenine-thymine and guanine-cytosine. They assume great importance in the processes of replication and transcription, these latter processes ensuring that the transmission of genetic material is carried out accurately. Hydrogen bonds help in the folding of proteins for structural stability and function.

2. Water Properties: All these aspects—the high heat capacity, cohesion, and adhesion of a substance like water—add up to the importance of the element for life because of quite rare liquid water as a result of the hydrogen bonding it allows. These are for the sustention, and creation of life, and to help in the facilitation of chemical reactions in the biological system.

3. Environmental science: Hydrogen bonding explains various environmental processes related to the solubility of gases in water and the behavior of certain pollutants. Hydrogen bonds affect the ability of water to be a solvent in different substances, thus impacting the dispersion and concentration of pollutants in various aquatic systems.

Of course, hydrogen bonding stands for one of the most unifying concepts beneath a broad horizon of phenomena, both natural and man-made, cutting across an enormous range of impacts from scientific disciplines like biology to materials science. This proves how important understanding molecular interactions and the behavior of substances is.

Some Solved Examples

Example 1

Question: Which of the following compounds has the least tendency to form hydrogen bonds?

1) HF
2) HCl
3) H2O
4) NH3

Solution: Hydrogen bonding occurs when a hydrogen atom is bonded to a highly electronegative atom like F, O, or N. These elements can form hydrogen bonds due to their high electronegativity. In the given options, HCl has chlorine, which is less electronegative than F, O, and N. Therefore, HCl has the least tendency to form hydrogen bonds. Hence, the answer is option (2) HCl.

Example 2

Question: HF has the highest boiling point among hydrogen halides because it has:

1) Strongest Van der Waals interaction
2) Lowest ionic character
3) Strongest hydrogen bonding
4) Lowest dissociation enthalpy

Solution: HF exhibits strong hydrogen bonding due to the high electronegativity of fluorine. This strong hydrogen bonding leads to a higher boiling point compared to other hydrogen halides like HCl, HBr, and HI, which primarily rely on weaker Van der Waals forces for intermolecular attractions. Therefore, the reason HF has the highest boiling point is due to its strongest hydrogen bonding. Hence, the answer is option (3) Strongest hydrogen bonding.

Example 3

Question: Which of the following hydrogen bonds is the strongest?

1) O-H---F
2) O-H---H
3) F-H---F
4) O-H---O

Solution: The strength of hydrogen bonds depends on the electronegativity of the atoms involved. Fluorine is the most electronegative element, making F-H---F the strongest hydrogen bond among the given options. Therefore, the strongest hydrogen bond is option (3) F-H---F.

Example 4

Question: The reason for the exceptionally high boiling point of water is:

1) Its high specific heat
2) Its high electric constant
3) Low ionization of water molecule
4) Hydrogen bonding in the molecule of water

Solution: Water has a high boiling point due to the presence of strong intermolecular hydrogen bonds. These hydrogen bonds result in a significant amount of energy being required to break them, leading to an exceptionally high boiling point. Thus, the reason for the high boiling point of water is option (4) Hydrogen bonding in the molecule of water.

Example 5

Question: Methanol and ethanol are miscible in water due to:

1) Covalent character
2) Hydrogen bonding character
3) Oxygen bonding character
4) None of these

Solution: Methanol and ethanol are miscible in water because they can form hydrogen bonds with water molecules. The hydroxyl group (-OH) in methanol and ethanol allows them to interact strongly with the water molecules, leading to complete miscibility. Therefore, the reason for their miscibility in water is option (2) Hydrogen bonding character.

Summary

One of the most important types of intermolecular forces is hydrogen bonding, characterized by an interaction of a hydrogen atom covalently attached to a very electronegative atom with another electronegative atom. Among characteristic properties, strength is envisaged to fall between the strongly bonded covalent and the much weaker Van der Waals forces. Further subdivision can be done into an intermolecular and intramolecular variety of hydrogen bonds; these participate massively in many different chemical and biological processes.

Frequently Asked Questions (FAQs)

1. How does the electronegativity of atoms affect hydrogen bonding?

Electronegativity plays a crucial role in hydrogen bonding. The bond must involve highly electronegative atoms like nitrogen, oxygen, or fluorine. The greater the electronegativity difference between hydrogen and the atom it's bonded to, the stronger the hydrogen bond can be with another electronegative atom.

2. Why can't hydrogen form hydrogen bonds with carbon in organic compounds?

Carbon isn't electronegative enough to form hydrogen bonds. Hydrogen bonding requires a large electronegativity difference between hydrogen and the atom it's bonded to. Carbon and hydrogen have similar electronegativities, so their bond isn't polarized enough to participate in hydrogen bonding.

3. Why is ice less dense than liquid water?

Ice is less dense than liquid water due to hydrogen bonding. In ice, water molecules form a crystalline structure with more space between them, making it less dense. In liquid water, molecules are more closely packed despite still having hydrogen bonds, resulting in higher density.

4. How does hydrogen bonding influence the evaporation rate of liquids?

Hydrogen bonding typically decreases the evaporation rate of liquids. The strong attractions between molecules make it harder for them to escape into the gas phase. This is why water, despite its low molecular weight, has a lower evaporation rate than many other liquids.

5. How does temperature affect hydrogen bonding?

Increasing temperature generally weakens hydrogen bonding. As temperature rises, molecules gain more kinetic energy, making it harder for them to form and maintain hydrogen bonds. This is why many properties influenced by hydrogen bonding, like viscosity and surface tension, decrease with increasing temperature.

6. What is hydrogen bonding?

Hydrogen bonding is a special type of intermolecular attraction between a hydrogen atom bonded to a highly electronegative atom (like nitrogen, oxygen, or fluorine) and another highly electronegative atom. It's stronger than typical intermolecular forces but weaker than covalent bonds.

7. What's the difference between a hydrogen bond and a covalent bond?

A hydrogen bond is an intermolecular force, while a covalent bond is intramolecular. Covalent bonds are much stronger, involve sharing of electrons, and hold atoms together within a molecule. Hydrogen bonds are weaker, don't involve electron sharing, and occur between separate molecules or parts of large molecules.

8. What role does hydrogen bonding play in the formation of micelles?

Hydrogen bonding plays a crucial role in micelle formation. In water, the hydrophilic heads of surfactant molecules form hydrogen bonds with water, while the hydrophobic tails cluster together. This arrangement, stabilized by hydrogen bonding, allows micelles to form and influences their properties.

9. How does hydrogen bonding contribute to the unique properties of water?

Hydrogen bonding gives water many of its unique properties, including high boiling and melting points, high specific heat capacity, high surface tension, and the ability to dissolve many substances. It also causes water to expand when it freezes, which is crucial for life in aquatic environments.

10. Can hydrogen bonding occur in non-polar solvents?

Hydrogen bonding can occur in non-polar solvents, but it's less common and often weaker. Molecules that can form hydrogen bonds (like small alcohols) may form hydrogen bonds with each other even in a non-polar solvent, which can affect their behavior and properties in that environment.

11. Why is hydrogen bonding important in water?

Hydrogen bonding is crucial in water because it gives water many of its unique properties. It causes water to have a high boiling point, high surface tension, and the ability to dissolve many substances. It also allows ice to float on liquid water, which is vital for aquatic life.

12. How does hydrogen bonding affect the boiling point of substances?

Hydrogen bonding typically increases the boiling point of substances. This is because the strong attractions between molecules require more energy to overcome, so a higher temperature is needed to convert the liquid to a gas. This is why water has a higher boiling point than similar-sized molecules without hydrogen bonding.

13. What makes hydrogen bonding different from other intermolecular forces?

Hydrogen bonding is stronger and more directional than other intermolecular forces like van der Waals forces. It occurs specifically between hydrogen and highly electronegative atoms, whereas other intermolecular forces can occur between any types of molecules.

14. How does hydrogen bonding contribute to the structure of proteins?

Hydrogen bonding is crucial in protein structure. It helps form and stabilize secondary structures like alpha helices and beta sheets. It also plays a role in tertiary structure by helping to fold the protein into its final three-dimensional shape.

15. What role does hydrogen bonding play in DNA structure?

Hydrogen bonding is essential in DNA structure. It forms between complementary base pairs (adenine-thymine and guanine-cytosine), holding the two strands of the DNA double helix together. This specific pairing is crucial for DNA replication and the storage of genetic information.

16. Can hydrogen bonding occur between different types of molecules?

Yes, hydrogen bonding can occur between different types of molecules, as long as one has a hydrogen bonded to a highly electronegative atom, and the other has a lone pair of electrons on a highly electronegative atom. For example, water can form hydrogen bonds with ammonia or ethanol.

17. Can hydrogen bonding occur within a single molecule?

Yes, hydrogen bonding can occur within a single molecule, which is called intramolecular hydrogen bonding. This happens in large molecules with multiple functional groups, like proteins and DNA. Intramolecular hydrogen bonding can affect a molecule's shape and properties.

18. Can hydrogen bonding occur in gases?

Yes, hydrogen bonding can occur in gases, although it's less common and generally weaker than in liquids or solids. For example, water vapor molecules can form hydrogen bonds, which affects properties like the gas's heat capacity and behavior under certain conditions.

19. How does hydrogen bonding affect the viscosity of liquids?

Hydrogen bonding typically increases the viscosity of liquids. The strong attractions between molecules make it harder for them to flow past each other, resulting in higher viscosity. This is why water is more viscous than many other liquids of similar molecular size.

20. How does hydrogen bonding affect the solubility of substances?

Hydrogen bonding can greatly increase the solubility of substances in water. Compounds that can form hydrogen bonds with water (like alcohols or ammonia) are generally more soluble than similar-sized molecules that can't. This is why "like dissolves like" is a useful rule in predicting solubility.

21. How does hydrogen bonding influence the surface tension of liquids?

Hydrogen bonding increases surface tension in liquids. The strong attractions between molecules at the surface create a "skin-like" effect, making it harder to break the surface. This is why water has a higher surface tension than many other liquids, allowing some insects to walk on water.

22. What's the relationship between hydrogen bonding and capillary action?

Hydrogen bonding contributes to capillary action. It allows water to adhere to surfaces (adhesion) and to itself (cohesion). These forces, combined with surface tension, enable water to climb up narrow tubes against gravity, which is important in many biological and physical processes.

23. How does hydrogen bonding affect the heat capacity of water?

Hydrogen bonding increases water's heat capacity. Breaking and reforming hydrogen bonds absorbs and releases energy, allowing water to absorb or release more heat with less temperature change. This property is crucial for temperature regulation in living organisms and in the Earth's climate.

24. How does hydrogen bonding affect the freezing point of liquids?

Hydrogen bonding typically raises the freezing point of liquids. The strong intermolecular attractions make it easier for molecules to align into a solid crystal structure at higher temperatures. This is why water freezes at a higher temperature than many other liquids of similar molecular size.

25. What's the difference between strong and weak hydrogen bonds?

The strength of hydrogen bonds varies depending on the electronegativity of the atoms involved and the geometry of the molecules. Strong hydrogen bonds typically involve fluorine, oxygen, or nitrogen, while weaker ones might involve chlorine or sulfur. Strong hydrogen bonds have more influence on a substance's properties.

26. How does hydrogen bonding affect the crystal structure of ice?

Hydrogen bonding determines the crystal structure of ice. Water molecules in ice form a hexagonal lattice held together by hydrogen bonds. This structure has more open space than liquid water, which is why ice is less dense and floats on water.

27. What role does hydrogen bonding play in the properties of alcohols?

Hydrogen bonding significantly influences alcohol properties. It causes alcohols to have higher boiling points, greater viscosity, and better water solubility than hydrocarbons of similar size. The strength of these effects generally increases with the number of hydroxyl groups in the alcohol molecule.

28. How does hydrogen bonding affect the mixing of liquids?

Hydrogen bonding can greatly affect liquid mixing. Liquids that can form hydrogen bonds with each other (like water and ethanol) tend to mix well. However, when one liquid can form hydrogen bonds and the other can't (like water and oil), they tend not to mix, leading to phase separation.

29. What's the relationship between hydrogen bonding and van der Waals forces?

Hydrogen bonding is a specific type of intermolecular force, while van der Waals forces are a broader category. Hydrogen bonds are typically stronger and more directional than van der Waals forces. However, both can coexist and contribute to the overall intermolecular attractions in a substance.

30. How does hydrogen bonding influence the properties of carboxylic acids?

Hydrogen bonding significantly affects carboxylic acid properties. It causes them to have higher boiling points and greater viscosity than expected for their molecular weight. Carboxylic acids can form hydrogen bonds with water (increasing solubility) and with each other (often forming dimers in non-polar solvents).

31. What role does hydrogen bonding play in the structure of cellulose?

Hydrogen bonding is crucial in cellulose structure. It occurs between the hydroxyl groups of adjacent cellulose chains, helping to align them and create strong, rigid fibers. This hydrogen bonding contributes to cellulose's strength and insolubility in water, making it an excellent structural material in plants.

32. How does hydrogen bonding affect the behavior of surfactants?

Hydrogen bonding influences surfactant behavior by allowing the hydrophilic head to interact strongly with water. This, combined with the hydrophobic tail's aversion to water, causes surfactants to arrange at interfaces and form structures like micelles, which is crucial for their cleaning and emulsifying properties.

33. What's the relationship between hydrogen bonding and hydrogen fuel cells?

While hydrogen fuel cells don't directly use hydrogen bonding, understanding hydrogen bonding is important in designing materials for fuel cells. For example, some proton exchange membranes rely on hydrogen bonding to facilitate proton transport, which is crucial for fuel cell operation.

34. How does hydrogen bonding contribute to the properties of nylon?

Hydrogen bonding plays a significant role in nylon's properties. It occurs between the amide groups of adjacent polymer chains, providing additional strength and flexibility to the material. This contributes to nylon's high tensile strength, durability, and resistance to wear and tear.

35. What role does hydrogen bonding play in the solubility of gases in water?

Hydrogen bonding affects gas solubility in water. Gases that can form hydrogen bonds with water (like ammonia or hydrogen fluoride) are generally more soluble than those that can't. However, extensive hydrogen bonding between water molecules can also make it harder for some gases to dissolve, as they must break these bonds to enter solution.

36. How does hydrogen bonding influence the properties of nucleic acids?

Hydrogen bonding is crucial in nucleic acid structure and function. It holds complementary base pairs together in DNA and RNA, determines the specificity of base pairing, and contributes to the stability of the double helix structure. It also plays a role in processes like DNA replication and transcription.

37. What's the relationship between hydrogen bonding and the anomalous expansion of water?

Hydrogen bonding causes water's anomalous expansion. As water cools below 4°C, the hydrogen bonds begin to form a more open, hexagonal structure. This causes water to expand as it freezes, unlike most substances which contract. This property is crucial for aquatic life, as it allows ice to float on water.

38. How does hydrogen bonding affect the properties of amines?

Hydrogen bonding influences amine properties significantly. Primary and secondary amines can form hydrogen bonds, leading to higher boiling points and greater water solubility than hydrocarbons of similar size. However, these effects are generally less pronounced than in alcohols due to nitrogen's lower electronegativity compared to oxygen.

39. What role does hydrogen bonding play in the structure of liquid crystals?

Hydrogen bonding can be important in some liquid crystal structures. It can help align molecules in certain directions, contributing to the ordered arrangement characteristic of liquid crystals. This can affect properties like the temperature range of the liquid crystal phase and the material's response to electric fields.

40. How does hydrogen bonding contribute to the properties of carbohydrates?

Hydrogen bonding is crucial in carbohydrate structure and properties. It occurs between the numerous hydroxyl groups in carbohydrates, influencing their solubility in water, their ability to form crystals, and their interactions with other molecules. In polysaccharides like cellulose, it contributes to the overall structure and properties of the molecule.

41. What's the relationship between hydrogen bonding and the pH of water?

Hydrogen bonding affects water's pH indirectly. It stabilizes the H+ and OH- ions formed by water's self-ionization, influencing the equilibrium constant for this process. This helps maintain water's neutral pH of 7 under standard conditions. Hydrogen bonding also plays a role in the behavior of acids and bases in aqueous solutions.

42. How does hydrogen bonding influence the properties of polymers?

Hydrogen bonding can significantly affect polymer properties. In polymers that can form hydrogen bonds (like nylon or cellulose), it provides additional strength and can influence characteristics like melting point, solubility, and mechanical properties. It can also affect how the polymer interacts with other substances, like water or dyes.

43. What role does hydrogen bonding play in enzyme-substrate interactions?

Hydrogen bonding is crucial in enzyme-substrate interactions. It helps enzymes recognize and bind to their specific substrates, contributing to the "lock and key" or "induced fit" models of enzyme action. These bonds can also stabilize the transition state during catalysis, lowering the activation energy of the reaction.

44. How does hydrogen bonding affect the properties of amino acids and proteins?

Hydrogen bonding greatly influences amino acid and protein properties. It contributes to the secondary, tertiary, and quaternary structures of proteins, affecting their shape and function. It also influences properties like solubility and the pKa values of amino acid side chains, which are important for protein function.

45. What's the relationship between hydrogen bonding and the greenhouse effect?

Hydrogen bonding in water vapor contributes to the greenhouse effect. Water vapor is a potent greenhouse gas partly because of its ability to form hydrogen bonds, which allows it to absorb infrared radiation across a wide range of wavelengths. This property helps water vapor trap heat in the Earth's atmosphere.

46. How does hydrogen bonding influence the properties of soap and detergents?

Hydrogen bonding is important in soap and detergent action. The polar head of soap molecules can form hydrogen bonds with water, while the non-polar tail interacts with oils and grease. This dual nature, facilitated by hydrogen bonding, allows soaps to emulsify oils and remove them from surfaces.

47. What role does hydrogen bonding play in the taste of water?

Hydrogen bonding contributes to water's taste indirectly. Pure water is tasteless, but the hydrogen bonding network in water can interact with dissolved minerals and gases, affecting how we perceive its taste. The strength of these interactions can vary with temperature, which is why the taste of water can seem different at different temperatures.

48. How does hydrogen bonding affect the properties of hydrogels?

Hydrogen bonding is crucial in hydrogel properties. It allows hydrogels to absorb large amounts of water without dissolving. The polymer network in hydrogels forms hydrogen bonds with water molecules, causing the gel to swell. This property is useful in applications like contact lenses, wound dressings, and drug delivery systems.

49. What's the relationship between hydrogen bonding and the hardness of water?

Hydrogen bonding indirectly affects water hardness. While hardness is primarily due to dissolved calcium and magnesium ions, these ions can interact with water molecules via hydrogen bonding. This can influence how the hardness ions interact with soap molecules and form scale, which are characteristic effects of hard water.

50. How does hydrogen bonding contribute to the properties of collagen?

Hydrogen bonding is essential in