Difference Between Intermolecular and Intramolecular Hydrogen Bonding

Main Difference – Intermolecular vs Intramolecular Hydrogen Bonding

Molecules are formed when atoms of either the same elements or different elements come together to share electrons and make covalent bonds. There are two types of attractive forces that keep the covalent molecules together. These are called intermolecular forces and intramolecular forces. Intermolecular forces are the attractive forces that occur between two molecules, whereas intramolecular forces occur within the molecule itself. Hydrogen bonds are special types of bonds that are formed in molecules made by a hydrogen atom sharing electrons with a highly electronegative atom. Hydrogen bonding can occur as both intermolecular and intramolecular forces. The main difference between intermolecular and intramolecular hydrogen bonding is that intermolecular bonding occurs between two neighbouring molecules whereas intramolecular hydrogen bonding occurs within the molecule itself.

It is important to know the function of these two forces separately to understand how they keep a molecule or a covalent compound together.

This article explains, 

1. What is Hydrogen Bonding?
2. What is Intermolecular Hydrogen Bonding?
        – Definition, Features and Properties, Examples
3. What is Intramolecular Hydrogen Bonding?
       – Definition, Features and Properties, Examples
4. What is the difference between Intermolecular and Intramolecular Hydrogen Bonding?

What is Hydrogen Bonding

When hydrogen, which is moderately electronegative, is covalently bonded to a strongly electronegative atom, the pair of the electrons they share becomes more biased towards the highly electronegative atom. Examples of such atoms are N, O, and F.  There must be a hydrogen acceptor and hydrogen donor for a hydrogen bond to be formed. The hydrogen donor is the highly electronegative atom in the molecule and the hydrogen acceptor is the highly electronegative hydrogen atom in the neighbouring molecule and should possess a lone pair of electrons.

Hydrogen bonding can appear either between two molecules or within the molecule. These two types are known as intermolecular hydrogen bonding and intramolecular hydrogen bonding respectively.

What is Intermolecular Hydrogen Bonding

Intermolecular hydrogen bonding can occur between like or unlike molecules. The position of the acceptor atom should be properly oriented such that it can interact with the donor.

Let’s look at a water molecule to understand the scenario clearly.

Figure 1: Hydrogen Bonding in Water Molecule

The pair of electrons shared between H and O atoms are more attracted towards the Oxygen atom. Hence, the O atoms get a slight negative charge compared to H atom. O atom is depicted as δ- and H atom is depicted as δ+. When a second water molecule comes near the former, an electrostatic bond is formed between the δ- O atom of one water molecule with δ+ H atom of the other. The oxygen atoms in the molecules behave as the donor (B) and acceptor (A) where one O atom donates hydrogen to the other.

Water has very special qualities due to hydrogen bonding. It is a good solvent and has a high boiling point and high surface tension. Further, ice at 4 ̊C is of lower density than water. Hence, ice floats on liquid water protecting the aquatic life beneath during the winter. Because of these features in water, it is called the universal solvent and plays a major role in maintaining life on earth.

What is Intramolecular Hydrogen Bonding

If a hydrogen bond occurs within two functional group of the same molecule, it is called an intramolecular hydrogen bond. This occurs when the hydrogen donor and the acceptor are both within the same molecule.

Figure 2: Structure of o-Nitrophenol (ortho-Nitrophenol) with intramolecular hydrogen bond

In the O-nitro phenol molecule, the O atom in the –OH group is more electronegative than the H and hence δ-. H atom, on the other hand, is δ+.  Therefore, the O atom in the –OH group acts as the H donor whereas O atom on the nitro group acts as the H-acceptor.

Difference Between Intermolecular and Intramolecular Hydrogen Bonding

Bond Formation

Intermolecular Hydrogen Bonding: Intermolecular hydrogen bonding occurs between two neighbouring molecules.

Intramolecular Hydrogen Bonding: Intramolecular hydrogen bonding occurs within the molecule itself.

Physical Properties

Intermolecular Hydrogen Bonding: Intermolecular hydrogen bonding has high melting and boiling points, and low vapour pressure. 

Intramolecular Hydrogen Bonding: Intramolecular hydrogen bonding has low melting and boiling points and high vapour pressure.

Stability

Intermolecular Hydrogen Bonding: The stability is comparatively high.

Intramolecular Hydrogen Bonding: The stability is comparatively low.

Examples

Intermolecular Hydrogen Bonding: Water, methyl alcohol, ethyl alcohol, and sugar are examples of intermolecular hydrogen bonding. 

Intramolecular Hydrogen Bonding: O-nitrophenol and salicylic acid are examples of intramolecular hydrogen bonding. 

Summary – Intermolecular vs Intramolecular Hydrogen Bonding

Compounds with intermolecular hydrogen bonds are more stable than compounds with intramolecular hydrogen bonds. Intermolecular hydrogen bonds are responsible for connecting one molecule with other and keeping them bound together. In opposite to that, when intramolecular hydrogen bonding occur, molecules are less available for interacting with each other and the molecules have a less tendency to stick together. This leads to a decrease of boiling point and melting point. Further, molecules with intramolecular hydrogen bonding are more volatile and have a higher vapour pressure comparatively.

Compounds with intermolecular hydrogen bonds are readily soluble in compounds in similar nature, whereas compounds with intramolecular hydrogen bonds do not dissolve readily.

Reference:

“Hydrogen Bonding.” Chemistry LibreTexts. Libretexts, 21 July 2016. Web. 07 Feb. 2017.

“Hydrogen Bonding: Acceptors and Donors.” University of Wisconsin, n.d. Web. 07 Feb. 2017.

“Inter and intra molecular hydrogen bonding in alcohols, carboxylic acids and other molecules and their significance.” Organic Chemistry. N.p., oct. 2012. Web. 07 feb. 2017.

“Strength of intramolecular vs intermolecular hydrogen bonds.” Chemistry Stack Exchange. N.p., 2013. Web. 07 Feb. 2017.

Image Courtesy:

“O-Nitrophenol Wasserstoffbrücke” By NEUROtiker – Own work (Public Domain) via Commons Wikimedia

“210 Hydrogen Bonds Between Water Molecules-01” By OpenStax College – Anatomy & Physiology, Connexions Web site. (CC BY 3.0) via Commons Wikimedia