Question

Do isomers have the same physical properties? Provide evidence.

Answer 1

Not necessarily.

Explanation

Isomers might differ in polarities. They will end up with different physical properties such as melting points.

Example:

• 1,2-dichlorobenzene  has a melting point of around -18 ~ -17 degrees celsius. (SynQuest)

• 1,4-dichlorobenzene (with two chlorine opposite to each other on a benzene ring) has a melting point of 52 ~ 54 degrees celsius. (SynQuest)

Both 1,4- and 1,2-dichlorobenzene contains two chlorine atoms connected to a benzene ring. The two molecules are structural isomers.

The two chlorine atoms are adjacent to each other in the 1,2 isomer. The molecule is asymmetric and polar.

The two chlorine align with an axis of symmetry in the 1,4 isomer. The molecule is symmetric. The dipoles would cancel out to produce a nonpolar molecule.

Dipole-dipole interactions are typically stronger than induced dipole in isomers. As a result, the 1,2 isomer has a higher melting point.