Intermolecular forces of methyl alcohol CH3OH

Answer

Table of Contents Show

Why Does Methanol (CH3OH) have Hydrogen Bonding?
Does Methanol (CH3OH) have London Dispersion Forces?
What are Intermolecular Forces?
Types of Intermolecular Forces
Hydrogen Bonding
Which one has stronger Intermolecular forces of attraction: Water or Methanol?
Comparison of Intermolecular Forces and Intramolecular Forces
Polarity of Methanol
Bonding in Methanol (CH3OH)
Uses of Methanol (CH3OH)

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Hint: Intermolecular forces refer to those forces that mediate interaction between the molecules and they include forces of attraction and repulsion which are supposed to act between the atoms or other neighbouring particles like atoms or ions. Different types of intermolecular forces include ionic bonds, Vander Waals dipole-dipole interaction, hydrogen bonding and Vander Waals dispersion forces.

Complete step by step answer:

The given compound methanol i.e. \[C{H_3}OH\] is polar in nature due to the presence of hydroxyl groups. In alcohols, the hydrogen bonds are formed owing to the existence of covalent bonds between oxygen atom and hydrogen atom in the hydroxyl group ( \[O--H\] ). Oxygen is highly electronegative and thus, attracts the electrons towards itself in \[O--H\] bonds. As the proton in the hydrogen atom slightly screens the action of the oxygen which pulls the electrons away from hydrogen, it results into a net positive charge over the hydrogen atom. As a result, there is a net negative charge on the oxygen atom which creates an imbalance of charge over the hydroxyl group. Thus, \[C{H_3}OH\] can be represented as:

Thus, the overall hydroxyl group is considered to be polar (similar to magnet) as it possesses two opposite charges on each end. The net positive hydrogen atom can attract the negative electron clouds readily from the oxygen atom placed adjacent to it. Unlike Van der Waals’ forces, hydrogen bond involves a permanent imbalance of charges and hence, results in permanent dipole attractions.The diagram below demonstrates hydrogen bonding in \[C{H_3}OH\] molecules.

Now, we will discuss other intermolecular forces present in \[C{H_3}OH\] . As \[C{H_3}OH\] is polar in nature, it possesses a non-zero dipole. We know that oxygen atom is more electronegative in comparison to carbon atom and also, \[C{H_3}\] is considered to be a good electron donating group, so there will be a partial positive charge on carbon while partial negative charge on oxygen (i.e, a dipole), leading to dipole-dipole interactions as shown below:

\[C{H_3}OH\] also experiences Van Der Waals dispersion forces though of very low magnitude. As we already know that when atoms or molecules are polarizable to a certain degree, some interactions occur from them when they are brought together as electrons are pushed about. As a result, intermolecular forces such as hydrogen bonding, dipole-dipole interaction and Vander Waals dispersion forces are present in \[C{H_3}OH\] .

Note: Hydrogen bonding in alcohols make them soluble in water. Alcohols with a smaller hydrocarbon chain are highly soluble in water while alcohols having a higher hydrocarbon chain are less soluble in water owing to increasing hydrophobicity of the alkyl chain.

Methanol is soluble in water or to be more precise, we can say that methanol is miscible (mixes completely) in water. This is possible mainly because of hydrogen bonding. Let us understand how it occurs.

If we take Methanol (CH3OH), it has a strong hydrogen bonding force acting between its molecules. Now when we add methanol to water, the superior intermolecular force acting between the molecules will also be H−Bonding.

Now, if we consider the general rule of Like-Dissolves-Like, these ether and water will dissolve in or mix with each other easily as both are capable of H−Bonding. Basically, the attraction between methanol and water is so strong that it is enough to overcome the water-water and methanol-methanol intermolecular forces of attraction.

To explain further, if we look at methanol or other alcohols, it consists of a nonpolar carbon chain and a polar OH group. If we write the chemical formula of methanol it will look like; CH3OH. Ethanol has a carbon chain and an OH group. The nature of water is that since it is polar it will attract the OH group. Meanwhile, the carbon chain will be repelled. What we can state here is that the solubility of methanol is determined by the stronger of the two forces.

Also Read: Hydroxide

To conclude, the strength of the attraction of the OH group makes methanol completely miscible in water. Any amount of methanol will usually dissolve in water. As for the limitation, the solubility of alcohols starts to decrease starting with the four-carbon butanol. Additionally, if we go beyond 7-carbon heptanol, then alcohols are said to be immiscible.

For Reference: You can have a look at the solubility chart for different alcohols below.

Name	Formula	Solubility
Butanol	C4H9OH	0.11
Pentanol	C5H11OH	0.030
Hexanol	C6H13OH	0.0058
Heptanol	C7H15OH	0.0008
Methanol	CH3OH	miscible
Ethanol	C2H5OH	miscible
Propanol	C3H7OH	miscible

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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.

Ionic interaction

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.

Hydrogen Bonding

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.

Check out H2O Lewis Structure, Geometry, Hybridization, and Polarity.

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.

For example,

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.