Concept:Intermolecular forces dictate phase transition temperatures like boiling and melting points.
Formula:$$ \text{R-O}^{\delta-}\text{-H}^{\delta+} \cdots \text{:O}^{\delta-}\text{(H)-R} $$
Solution:- Alkanes are non-polar and rely solely on weak London dispersion (Van der Waals) forces.
- Alcohols contain a highly polarized O-H bond.
- The partially positive hydrogen of one molecule forms a very strong dipole-dipole attraction with the lone pair of the highly electronegative oxygen on an adjacent molecule.
- This specific, extraordinarily strong intermolecular force is termed hydrogen bonding, requiring significant thermal energy to break, thus raising the boiling point dramatically.
Why other options are incorrect:While alcohols have dipole-dipole and Van der Waals forces, hydrogen bonding is the primary and strongest force responsible for the massive difference compared to alkanes. Ionic interactions do not exist in covalent alcohols.
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