# Why does dimethyl sulfoxide have higher boiling point than acetone?

They have very similar structure except for a central atom, but the difference in boiling points is very large $$(\pu{186 ^\circ C}$$ for DMSO and $$\pu{56 ^\circ C}$$ for acetone).

How is central atom impacting the boiling point?

• Checkout the geometry of both molecules and also identify the polar bonds. Now figure out how dipole moment and boiling points relate. – Robin Singh Sep 7 '20 at 12:48
• thanks @RobinSingh for the help – Maxwell Sep 7 '20 at 13:33

Secondly, if we compare the dipole moments of the $$\ce{S=O}$$ and $$\ce{C=O}$$ bonds, the $$\ce{S=O}$$ bond is much more polarised. This is because the $$\mathrm{3p-2p}$$ overlap between $$\ce{S}$$ and $$\ce{O}$$ is much less favourable than the $$\mathrm{2p-2p}$$ overlap between $$\ce{C}$$ and $$\ce{O}$$. As such, the resonance structure on the right is actually the more significant resonance structure. This makes the $$\ce{S=O}$$ bond much more polarised as compared to the $$\ce{C=O}$$ bond, causing the permanent dipole-permanent dipole interactions between DMSO to be much stronger than the same interactions between acetone molecules.
• @user85426: There is another point you forgot, the boiling point is also depends on the molar mass of the compound. Difference in MM: $78.13$ versus $\pu{58.08 gmol-1}$. – Mathew Mahindaratne Sep 7 '20 at 18:59