Saved Bookmarks
| 1. |
Arrange the following compounds in increasing order of their boiling points: CH_(3)CHO,CH_(3)CH_(2)OH,CH_(3)OCH_(3),CH_(3)CH_(2)CH_(3). |
| Answer» Solution :The molecular masses of all these compounds are comparable: `CH_(3)CHO(44),CH_(3)CH_(2)OH(46),CH_(3)COCH_(3)(46),CH_(3)CH_(2)CH_(3)(44).` `CH_(3)CH_(2)OH` undergoes extensive intermolecular H-bonding. Therefore, it EXISTS as an associated MOLECULE and hence its b.p. is the highest (351 K). `CH_(3)CHO(mu=2.72D)` is more polar than `CH_(3)OCH_(3) (mu=1.18D)`, therefore, dipole-dipole interactions are stronger in `CH_(3)CHO` than in `CH_(3)OCH_(3)` and hence the boiling point of `CH_(3)CHO(293K)` is MUCH higher than that of `CH_(3)OCH_(3)(249K)`. Further molecules of `CH_(3)CH_(2)CH_(3)` have only weak van der waals FORCES while the molecules of `CH_(3)OCH_(3)` have little stronger dipole-dipole interactions and hence the b.p. of `CH_(3)OCH_(3)` is higher (249K) than that of `CH_(3)CH_(2)CH_(3)(231K)`. thus, the overall increasing order of boiling points is: `CH_(3)CH_(2)CH_(3) lt CH_(3)OCH_(3) lt CH_(3)CHO lt CH_(3)CH_(2) OH`. | |