Q49 / 180 · AIIMS 2001 · Chemistry

Assertion : $\mathrm{CH}_3 \mathrm{OCH}_3$ and $\mathrm{C}_2 \mathrm{H}_5 \mathrm{OH}$ has comparable molecular weight but boiling point of $\mathrm{C}_2 \mathrm{H}_5 \mathrm{OH}$ is more than dimethyl ether. Reason : $\mathrm{C}_2 \mathrm{H}_5 \mathrm{OH}$ forms intermolecular Hbonding while $\mathrm{CH}_3 \mathrm{OCH}_3$ forms intramolecular $\mathrm{H}$-bonding.

  • A
    If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
  • B
    If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
  • Correct answer
    C
    If Assertion is true but Reason is false.
  • D
    If Assertion is false but Reason is true.

Solution

Due to the presence of hydroxyl group $(-\mathrm{OH})$, there is extensive hydrogen bonding between the ethanol molecules $\left(\mathrm{C}_2 \mathrm{H}_5 \mathrm{OH}\right)$. But there is no such hydrogen bonding in dimethyl ether (due to absence of -OH group). So boiling point of dimethyl ether is much lower than ethanol.

Hence, the correct answer is option: 'C'.

Relevant Questions