Question

Arrange the following compounds in the order of properties mentioned: a) Pentan-1-ol, Pentan-2-ol, ethanol, Propan-1-ol and methanol.(increasing order of boiling point

Answer 1

Dear student,

Boiling point of alcohol depends on the number of carbon atoms present in the alcohol. As the number of carbon atom increases, boiling point also increases. With the increase in the number of carbon atoms, van der waal's forces and surface area of the molecule increases, thus boiling point increases.
Methanol ( CH₃-OH) has one carbon atom.
Ethanol ( C₂-H₅-OH) has two carbon atoms.
Propan-1-ol (CH₃-CH₂-CH₂-OH) has three carbon atoms.
Pentan-1-ol ( CH₃-CH₂-CH₂-CH₂-CH₂-OH) has five carbon atoms.
Pentan-2-ol (CH₃-CH₂-CH₂-CH(OH)-CH₃) has five carbon atoms.


Pentan-1-ol and pentan-2-ol both have 5 carbon atoms but pentan-2-ol has -OH substituent at position 2 due to which surface area of the alcohol decreases with respect to pentan-1-ol.

Keeping in mind the number of carbon atoms, we can write the sequence for boiling point as follows:

Methanol < Ethanol < Propan-1-ol < Pentan-2-ol < Pentan-1-ol

Regards