Chem questions

1.
The answer is: A. (1), (4), (3), (2)

The molecules of (1) and (4) are non-polar, and thus they have weak instantaneous dipole - induced dipole attractions between their molecules. Such attraction is the weakest intermolecular force, and thus (1) and (4) have the lowest boiling points among the four compounds. Since the molecular size of (4) is greater than that of (1), thus the instantaneous dipole - induced dipole attractions in (4) is greater than those in (1). Therefore, the boiling point of (4) is higher than that of (1).

The molecules of (2) are held together by intermolecular hydrogen bonds, and such attraction is the strongest intermolecular force. Therefore, (2) has the highest boiling point among the four compounds.

The molecules of (3) are polar, and they are held together by dipole-dipole attraction. Such attraction is weaker than that in (2), but stronger than that in (4). Therefore, the melting point of (3) is lower than that of (2), but higher than that of (4).

2010-11-30 00:17:32 補充：
The polarity of hydrocarbon molecule is low as the electronegativity of carbon is close to that of hydrogen, and thus hydrocarbon molecules are thought to be non-polar.

2010-11-30 20:51:20 補充：
It is only necessary to consider the dipole moments which cannot be cancelled by other dipole moments.