What is the Difference Between Propan-1-ol and Propan-2-ol?

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Propan-1-ol and propan-2-ol are both alcohols that share the same general chemical formula (C3H8O), so what is the difference between them exactly? It all comes down to their atomic arrangement and how the hydroxyl group is positioned.

In a nutshell, the difference between propan-1-ol and propan-2-ol is the position of their respective hydroxyl (-OH) groups. Propan-1-ol has an –OH group attached to its terminal carbon atom while propan-2-ol has an –OH group attached to its middle carbon atom.

This small difference in chemical structure is enough to make a noticeable impact in the way these two alcohols behave, in the way they can be used and in the way they are categorised.

What Are Alcohols?

Alcohols are chemical compounds that contain carbon and hydrogen atoms as well as a hydroxyl group (-OH). There are many different types of alcoholic compounds and each one can be put into one of three categories: primary, secondary or tertiary.

The category of an alcohol is determined by the position of the hydroxyl group. For example, if the hydroxyl group is attached to a primary or terminal carbon atom, i.e. one that is at either end of the carbon chain, then it is a primary alcohol. If the hydroxyl group is attached to any other carbon atom, not at the end of the chain, then it is classified as either secondary or tertiary.

The name of an alcohol is derived from the number of carbon and hydrogen atoms as well as the alkane backbone that the hydroxyl group attaches to. For example, an –OH group attaches to an:

  • Ethane (C2H6) backbone to form ethanol (C2H6O) a.k.a. ethyl alcohol
  • Methane (CH4) backbone to form methanol (CH3OH) a.k.a. methyl alcohol
  • Butane (C4H10) backbone to form butanol (C4H10O) a.k.a. butyl alcohol
  • Propane (C3H8) backbone to form propanol (C3H8O) a.k.a. propyl alcohol

These four compounds are the simplest alcohols and also the most common, but their different structures give them each different properties.

What is Propanol?

The molecular structure of propanol is comprised of a 3-carbon backbone that 8 hydrogen atoms, including a hydroxyl group, are attached to.

However, the propanol molecule can occur in 2 different forms. This means there are 2 isomers of propanol, and they can be identified by the position of the hydroxyl group on the carbon backbone:

  • Propan-1-ol has its –OH group attached to the terminal carbon atom of the molecule
  • Propan-2-ol has its –OH group attached to the middle carbon atom of the molecule

While they do have certain similarities, the structural nuances between the two molecules cause differences in the properties of propan-1-ol and propan-2-ol.

Propan-1-ol

Also known as 1-propanol, this compound is a primary alcohol that is most commonly used as a solvent in the pharmaceutical industry.

Although it has the general formula C3H8O, its specific molecular structure can also be expressed as CH3CH2CH2OH to show that the hydroxyl group is attached to a terminal carbon atom. This is what categorises propan-1-ol as a primary alcohol.

Properties

Physically, propan-1-ol appears as a colourless liquid at room temperature and it is characterised by a fruity flavour and mildly alcoholic smell. Chemically, it is a primary alcohol and an isomer of propan-2-ol. Other notable properties include:

  • Melting Point: -126°C
  • Boiling Point: 97.2°C
  • Molar Mass: 60.1 g/mol
  • High rate of esterification
  • Difficult to dehydrate

Chemical Structure

Structurally, propan-1-ol has 3 carbon atoms bonded to each other. This forms the backbone of the molecule. Its structure is only comprised of single bonds, making it a saturated compound.

Because the hydroxyl group is connected to a terminal carbon atom, i.e. a carbon atom positioned at the end of the carbon chain, propan-1-ol is a primary alcohol. As a primary alcohol, it forms aldehydes when it undergoes oxidation and it is more acidic than other alcohol categories.

Propan-2-ol

Most commonly known as isopropyl alcohol (IPA) or isopropanol, propan-2-ol is a secondary alcohol that has a wide range of applications across many different industries.

Like propan-1-ol, its general formula is C3H8O but it can also be structurally expressed as CH3CH(OH)CH3 to show that the hydroxyl group is attached to a middle carbon atom instead of a terminal one. This is what makes propan-2-ol a secondary alcohol.

Properties

Propan-2-ol is not dissimilar to propan-1-ol in that it appears as a colourless liquid at room temperature. It can be physically distinguished from propan-1-ol by its comparatively pleasant odour and its bitter, instead of fruity taste.

Chemically, propan-2-ol is a secondary alcohol and a structural isomer of propan-1-ol. Other notable properties include:

  • Melting Point: -89°C
  • Boiling Point: 82.6°C
  • Molar Mass: 60.1 g/mol
  • Low rate of esterification
  • Easier to dehydrate than propan-1-ol

Chemical Structure

Structurally, propan-2-ol also has a backbone of 3 carbon atoms bonded together. Like propan-1-ol, this is also a saturated compounded because it only has single bonds. The only difference in structure between these two isomers is the positioning of the hydroxyl group.

Because the –OH group is attached to a middle carbon atom, propan-2-ol is classed as a secondary alcohol. As a secondary alcohol, propan-2-ol is generally more reactive, more stable and less acidic than propan-1-ol. It also forms ketones instead of aldehydes when it undergoes oxidation.

Similarities

While there are many differences between these two compounds, they also share several similarities:

  • They are both alcoholic compounds
  • They both have the same formula
  • They both contain three carbon atoms
  • They both contain eight hydrogen atoms
  • They both contain a hydroxyl group
  • They are both colourless liquids
  • They have the same molar mass
  • They can both be used as solvents

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ReAgent are leading manufacturers of propan-2-ol and are internationally recognised for our uncompromising quality. We stock propan-2-ol in a range of pack sizes and grades. Whether you need it for analytical use, laboratory use or general use, we have the product that’s right for you.

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