Hydrogen Bonding and Their Types

Hydrogen Bonding

Hydrogen bond is a type of dipole-dipole interaction between very high electronegative atom (i.e. N, O and F) and a hydrogen atom bonded to another electronegative atom. This bond always involves a hydrogen atom. Hydrogen bonds can occur between molecules or within a single molecule.

Hydrogen bond is stronger than van der Waals forces, but weaker than covalent bonds or ionic bonds. It is about 5% the strength of the normal covalent bond formed between O-H.

Types of Hydrogen Bonding

There are two types of Hydrogen bonds. They are-

Intermolecular Hydrogen Bonding
Intramolecular Hydrogen Bonding

1. Intermolecular Hydrogen Bonding:

When hydrogen bonding takes place between different molecules of the same or different compounds, it is called intermolecular hydrogen bonding. For example – hydrogen bonding in water, alcohol, ammonia, p-nitrophenol etc.

2. Intramolecular Hydrogen Bonding:

The hydrogen bonding which takes place within a molecule itself is called intramolecular hydrogen bonding.
It takes place in compounds containing two groups such that one group contains hydrogen atom linked to an electronegative atom and the other group contains a highly electronegative atom linked to a lesser electronegative atom of the other group. The bond is formed between the hydrogen atoms of one group with the more electronegative atom of the other group.
For example – ortho-nitrophenol, Salicylic acid, Salicyldehyde etc.

MCQs Based on Hydrogen Bonding

Which of the following conditions is most essential for the formation of a hydrogen bond?

A. The presence of an atom with high electronegativity.
B. The presence of a hydrogen atom bonded to a highly electronegative atom.
C. The presence of a lone pair of electrons on the hydrogen atom.
D. The presence of a strong ionic bond.

Option B is correct answer.

Explanation: A hydrogen bond forms when a hydrogen atom, already covalently bonded to a highly electronegative atom (N, O, or F), is attracted to another highly electronegative atom in a different or the same molecule that possesses a lone pair of electrons.

Why does NH₃ have a higher boiling point than PH₃?

A. PH₃ is more polar
B. NH₃ forms hydrogen bonds, PH₃ does not
C. PH₃ has a higher molecular mass
D. NH₃ is a larger molecule

Option B is correct answer.

Explanation: NH₃ can form hydrogen bonds due to the high electronegativity of nitrogen, while PH₃ cannot.

Which of the following molecules is least likely to exhibit intermolecular hydrogen bonding?

A. Water
B. Ammonia
C. Methane
D. Hydrogen Fluoride

Option C is correct answer.

Explanation: Hydrogen bond requires a hydrogen atom bonded to a highly electronegative atom (N, O, or F). In methane, hydrogen is bonded to carbon, which has similar electronegativity to hydrogen, resulting in very little polarity in the C-H bond and thus no hydrogen bonding. Water, ammonia, and hydrogen fluoride all have H atoms bonded to highly electronegative O, N, and F, respectively.

Which of the following statements about hydrogen bonding is correct?

A. It is a type of covalent bond
B. It is stronger than ionic bonds
C. It is a special type of dipole-dipole interaction
D. It occurs between any two hydrogen atoms

Option C is correct answer.

Explanation: Hydrogen bonding is a special dipole-dipole interaction between hydrogen and a highly electronegative atom.

The high boiling point of water compared to hydrogen sulphide is due to:

A. Stronger van der Waals forces in water.
B. The smaller size of the oxygen atom.
C. The presence of extensive hydrogen bonding in water.
D. The covalent nature of the O-H bond.

Option C is correct answer.

Explanation: Oxygen is much more electronegative than sulphur. This leads to highly polarized O-H bonds in water, allowing for strong hydrogen bonding between water molecules. Hydrogen sulphide has weaker dipole-dipole interactions and London dispersion forces but no significant hydrogen bonding due to lower electronegativity of sulphur, resulting in a much lower boiling point.

Which of the following types of hydrogen bonding is responsible for the secondary structure in proteins?

A. Intramolecular hydrogen bonding
B. Intermolecular hydrogen bonding
C. Covalent hydrogen bonding
D. Ionic hydrogen bonding

Option A is correct answer.

Explanation: The secondary structure of proteins is formed by hydrogen bonds between the hydrogen atom of an N-H group and the oxygen atom of a C=O group within the same polypeptide chain. This is a form of intramolecular hydrogen bonding, where the bonding occurs within a single large molecule, leading to specific folding patterns like α-helices and β-pleated sheets. Intermolecular hydrogen bonding would occur between different protein molecules.

Consider the following compounds:
I. Ethanol
II. Dimethyl Ether
III. Ethane
Which of these compounds can form hydrogen bonds with water molecules?

A. I only
B. I and II only
C. II and III only
D. I, II, and III

Option B is correct answer.

Explanation: Ethanol contains an -OH group. The hydrogen atom is bonded to a highly electronegative oxygen, allowing it to form hydrogen bonds with water's oxygen atoms, and water's hydrogen atoms can form bonds with ethanol's oxygen atom.
Dimethyl ether contains an oxygen atom with lone pairs, which can act as a hydrogen bond acceptor from water's hydrogen atoms. Although it doesn't have a hydrogen atom directly bonded to oxygen, it can still participate in hydrogen bonding with water.
Ethane consists only of C-H and C-C bonds. Carbon is not sufficiently electronegative to create the necessary polarity for hydrogen bonding.
Therefore, both ethanol and dimethyl ether can form hydrogen bonds with water.

The dissolution of ammonia in water is largely attributed to:

A. Formation of ionic bonds.
B. London dispersion forces.
C. Extensive hydrogen bonding between ammonia and water molecules.
D. The exothermic nature of the dissolution process.

Option C is correct answer.

Explanation: Both ammonia and water are capable of forming hydrogen bonds. Ammonia can act as both a hydrogen bond donor (via its N-H bonds) and acceptor (via the lone pair on nitrogen), while water can do the same (via O-H bonds and lone pairs on oxygen). This strong intermolecular hydrogen bonding between ammonia and water molecules leads to high solubility.

In which of the following conditions hydrogen bonding strengthen the most significantly?

A. From liquid methane to gaseous methane
B) From liquid ammonia to solid ammonia
C) From liquid hydrogen sulphide to gaseous hydrogen sulphide
D) From liquid methanol to gaseous methanol.

Option B is correct answer.

Explanation: Hydrogen bonding is an intermolecular force. These forces are strongest in the solid state, weaker in the liquid state, and weakest (almost negligible) in the gaseous state. Therefore, transitioning from liquid ammonia to solid ammonia would involve the most significant strengthening of hydrogen bonds as molecules become more rigidly arranged and closer to each other. The other options involve transitions to the gaseous state where hydrogen bonding weakens, or involve methane and hydrogen sulphide which do not exhibit significant hydrogen bonding.

In which of the following molecules does intramolecular hydrogen bonding occur?

A. Water
B. o-Nitrophenol
C. Ammonia
D. Methanol

Option B is correct answer.

Explanation: Intramolecular hydrogen bonding is present when a hydrogen atom is between two electronegative atoms within the same molecule, as in o-nitrophenol.

Hydrogen Bonding and Their Types