Question

Arrange the following compounds in decreasing order of their boiling points
$CH_3CHO, CH_3CH2OH, CH_3OCH_3, CH_3CH_2CH_3$

• A. $CH_3CH_2CH_3 < CH_3OCH_3 < CH_3CHO$
  $ \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, < CH_3CH_2OH$
• B. $CH_3CH_2CH_3 < CH_3CHO < CH_3OCH_3$
  $ \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, < CH_3CH_2OH$
• C. $CH_3CH_2CH_3 > CH_3CHO > CH_3OCH_3$
  $ \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, < CH_3CH_2OH$
• D. $CH_3CH_2CH > CH_3CHO > CH_3OCH_3$
  $ \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, < CH_3CH_2CH_3$

Answer 1

Answer: (B)

Among these only $CH_3CH_2OH$ undergoes H-bonding. So, it will have the highest boiling point. In thd case of remaining compounds, $H_3COCH_3$ has the highest \molecular weight, then $H_3CCHO$ and lastly $H_3CCH_2CH_3. \, OH_3CHO$ has higher boiling point than alkane due to apprciable intermolecular attraction ( dipole-dipole interaction).