Methanol is an organic compound. It is the first member of homologous series of saturated alcohol.
It is a colorless, volatile liquid with a characteristic odor and mixes with water.
Robert Boyle first isolated pure methanol in 1661 by distillation of wood.
It is commonly used as a polar solvent and in making other chemicals.
Methanol is produced from syngas at an industrial level. It is also released naturally from microbes, vegetation, and volcanic gases.
In this article, we will study the concept of intermolecular forces and identify the intermolecular forces for methanol.
So, what are the intermolecular forces in methanol? Methanol interacts with other molecules through hydrogen bonding due to the development of a significant positive charge on the hydrogen atom due to its bond with a highly electronegative oxygen atom. London forces are also present, but contribution is not significant.
There is a lot more to know about the intermolecular forces of methanol. Let’s deep dive and check out the chemistry behind it in further subheadings.
Why Does Methanol (CH3OH) have Hydrogen Bonding?
Methanol is a polar molecule and has a permanent dipole moment.
In methanol, H is bonded to O, which is highly electronegative. H develops a partial positive charge while O develops a partial negative charge therefore hydrogen atom interacts with the oxygen atom of another methanol molecule through hydrogen bonding.
One methanol molecule forms three hydrogen bonds, two through the oxygen atom (as proton acceptor) and one through H (as proton donor).
Does Methanol (CH3OH) have London Dispersion Forces?
Along with hydrogen bonds, methanol also interacts through London forces, but London forces’ magnitude is much smaller than hydrogen bonds.
The contribution of London forces increases with the increase in the length of the carbon chain.
London forces are generally neglected for methanol.
What are Intermolecular Forces?
Commonly, matter exists as solid, liquid, or gas. They exist in these different forms because of various reasons. One of the reasons is intermolecular forces.
Forces can be attractive or repulsive. When the force of attraction is much greater than the force of repulsion, molecules are strongly attracted to each other and exist as a solid. When the force of repulsion is greater than the force of attraction, it exists as a gas. A substance exists as a liquid in intermediate conditions.
In this article, we will discuss attractive forces. Intermolecular forces are those forces that hold together the molecules of a substance. In solids and liquids, intermolecular forces are responsible for keeping the molecules together.
No atom or molecule exists in isolation in nature, they interact with neighboring molecules through intermolecular forces.
The kind of forces decides the physical properties of a substance. For instance, if the forces are strong, the melting and boiling point would be high as more energy would be required to break their association.
Types of Intermolecular Forces
The strength of intermolecular forces depends on the magnitude of charges. These intermolecular forces are due to attraction between positively charged and negatively charged parts.
Methanol interacts through Van der Waals forces, and therefore we will discuss these forces in detail.
In the case of ions, complete charges are present on the atoms, and hence the strength of the force is higher than in neutral polar and non-polar compounds.
When an ionic compound comes near a neutral compound, it induces a polarity.
The side near the ionic compound develops an opposite charge and interacts through ion-dipole forces.
Van der Waals interaction
The attractive intermolecular forces that depend on the inverse sixth power of separation between molecules are called Van der Waals forces. The various types of Van der Waals forces are as follows-
• Dipole-dipole forces– These forces are present between the substances with a permanent dipole moment.
The ends of dipole possess partial charges with opposite signs. When a polar molecule comes near another polar molecule, the ends with opposite charges interact through dipole-dipole forces.
For instance, when two HCl molecules are brought closer, they interact through dipole-dipole forces as one molecule’s Cl side (partial negative) attracts the H side (partial positive) of the other.
Related Topic: Is HCl Ionic or Covalent
• Hydrogen bonding– It is a special form of dipole-dipole interaction.
For example, the interaction between water molecules is through hydrogen bonding.
• Dipole-induced dipole- This type of force exists between a polar and a non-polar molecule.
The dipole is created on a polar molecule by developing partial charges.
When this polar molecule comes near the non-polar molecule, the electron cloud of the non-polar molecule is distorted in such a way that it also develops partial charges. The non-polar molecule becomes an induced dipole. The force of attraction between a polar molecule and an induced dipole is dipole-induced dipole forces.
For example, the interaction between HCl (polar) and Ar atoms (non-polar) is dipole-induced dipole type.
• London forces– This type of force exist between all molecules. It is the weakest type of Vander Waals forces.
The non-polar molecules are symmetrical and can develop a temporary dipole moment.
When the electronic distribution changes in a non-polar molecule momentarily, the neighboring non-polar molecule develops an instantaneous dipole moment.
This force of attraction between two non-polar molecules is called London or dispersion force.
For instance, the interaction between methane molecules is of the London forces type.
Methane (CH4) is an example of this type of intermolecular force. Check out CH4 intermolecular force.
For hydrogen bonding to occur, H should be bonded to a highly electronegative element which develops a partial negative charge, and hydrogen develops a partial positive charge. Another electronegative atom of a different or same molecule interacts with H through hydrogen bonding.
The optimum bond angle for hydrogen bond formation is 180°. The strength of the hydrogen bond decreases with changing angle.
It is the strongest type of Vander Waals force.
It is not actual bonding; it is an electromagnetic interaction between partial negative and partial positive charges.
Hydrogen bonding determines the various properties of a substance. Lower alcohols like methanol are soluble in water due to hydrogen bonding.
Water is a liquid, while hydrogen sulfide is gas because of hydrogen bonding.
Mainly, there are two types of hydrogen bonding-
• Intramolecular Hydrogen bonding occurs when hydrogen bonding takes place between different atoms of the same compound.
• Intermolecular hydrogen bonding occurs when hydrogen bonding takes place between atoms or molecules of different compounds.
Which one has stronger Intermolecular forces of attraction: Water or Methanol?
Both water and methanol interact with other molecules of the same kind through hydrogen bonding.
Water can form hydrogen bonds with four other water molecules, while methanol can form hydrogen bonds with three other methanol molecules.
Thus, water has a stronger hydrogen bonding and hence stronger intermolecular forces of attraction than methanol.
Comparison of Intermolecular Forces and Intramolecular Forces
An intermolecular force of attraction or repulsion refers to the force between two molecules. Water exists in the form of a liquid because of intermolecular forces of attraction (hydrogen bonding) between different water molecules.
Intramolecular force refers to the force responsible for binding one molecule together.
Intramolecular force in methanol– the covalent bond between C & H, C & O, and O & H, which makes the molecule
Intermolecular force in methane– hydrogen bonding and dispersive forces between two methanol molecules
Polarity of Methanol
The polarity of a compound depends on the presence or absence of net dipole moment. The net dipole moment depends on
• The dipole moment of the bond
• The difference in electronegativity of the atoms forming a bond
• Geometry and symmetry
All the bonds are formed between different elements, and hence there is a difference in electronegativity. The electronegativity of C, H, and O are 2.55, 2.2, and 3.44, respectively. Hence, all the bonds are polar.
However, polar bonds do not guarantee a polar molecule. Methanol’s shape is tetrahedral but not symmetrical as it has 3 bonds with -H and one -OH bond. Thus, dipole moments do not cancel each other out, and it is a polar molecule.
It can develop positive and negative poles.
I have also written a specific article on Is Methanol Polar or Nonpolar?
Bonding in Methanol (CH3OH)
It is a covalent molecule as the difference in electronegativity of the atoms forming a bond is not large enough.
In methanol, both O and C are sp3 hybridized.
In C, the 2s and 2p orbitals overlap to form hybrid orbitals. 3 of them overlap with 1s orbital of hydrogen, and the fourth overlaps with the sp3 hybrid orbital of O.
In O, the 2s and 2p orbitals also overlap to form hybrid orbitals. Two-hybrid orbitals contain lone pair, one overlaps with s orbital of hydrogen, and one of them overlaps with the sp3 hybrid orbital of C.
Methanol has a tetrahedral geometry as it is a molecule of AX4 type where a central atom has four side atoms and no lone pairs.
Check out the article on CH3OH Lewis Structure, Hybridization, Geometry.
Uses of Methanol (CH3OH)
• It is used to prepare various chemicals like formaldehyde and acetic acid.
• It is used as an antifreeze in automobiles.
• It is used as rocket fuel.
• It is commonly used in the laboratory as an organic solvent.
• It is used for making industrial ethanol unfit for consumption.
• It is used in TV screens and mobile phones.
Methanol interacts with another methanol molecule through hydrogen bonding and London dispersive forces.
One methanol molecule can interact with three other methanol molecules through hydrogen bonding.
London forces are negligible in comparison to hydrogen bonding.
The strength of intermolecular forces follows the order-
Ion-ion > ion-dipole > hydrogen bond > dipole-dipole > dipole-induced dipole > induced dipole-induced dipole
Intermolecular forces hold various molecules together, while intramolecular forces hold together atoms in a molecule.
Methanol is a polar molecule and has a permanent dipole moment.
Methanol has a tetrahedral geometry, and C and O are sp3 hybridized.
Methanol is a very useful compound in the laboratory.