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Hydrogen bonding is a special type of dipole–dipole interaction that occurs between a hydrogen atom covalently bonded to a highly electronegative atom (such as oxygen, nitrogen, or fluorine) and another electronegative atom having a lone pair of electrons. This intermolecular force is stronger than van der Waals forces and greatly affects the physical and chemical properties of compounds.
Among the given options, ethanol (C₂H₅OH) shows hydrogen bonding. Ethanol contains a hydroxyl group (–OH), where the hydrogen atom is directly bonded to an electronegative oxygen atom. The oxygen atom has lone pairs of electrons, and the O–H bond is highly polar. As a result, hydrogen from one ethanol molecule can form a strong intermolecular attraction with the oxygen atom of another ethanol molecule. This type of bonding is called hydrogen bonding.
Hydrogen bonding in ethanol explains several of its unique properties:
High boiling point: Ethanol has a higher boiling point compared to other compounds of similar molecular weight because extra energy is required to break hydrogen bonds between molecules.
High solubility in water: Ethanol is completely miscible with water because it can form hydrogen bonds with water molecules, creating a strong interaction between ethanol and water.
Strong intermolecular attraction: This results in higher surface tension and higher viscosity compared to non-hydrogen-bonded compounds.
Now, analyzing the other options:
Ethane (C₂H₆): Contains only C–H bonds, which are non-polar and cannot form hydrogen bonds.
Ethyl chloride (C₂H₅Cl): The C–Cl bond is polar, but chlorine does not easily form hydrogen bonds with hydrogen atoms in this structure.
Dimethyl ether (CH₃OCH₃): Contains oxygen, but no hydrogen directly bonded to oxygen, so it cannot form hydrogen bonds between its own molecules (though it can accept hydrogen bonds from water).
Therefore, among the listed compounds, only ethanol (C₂H₅OH) exhibits strong hydrogen bonding due to its hydroxyl group. This property makes ethanol one of the most important examples of hydrogen bonding in organic chemistry.
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